OCS Study 

MMS 2001-095 

Coastal Marine Institute 

Management Applicability of 

Contemporary Deep-Sea Ecology and 

Reevaluation of Gulf of Mexico Studies 

U.S . Department of the Interior Cooperative.Agreement me

Minerals Management Service Coastal Marine Institute 

Adw Gulf of Mexico OCS Region Louisiana State University 
OCS Study 

MMS 2001-095 

Coastal Marine Institute 

Management Applicability of 

Contemporary Deep-Sea Ecology and 

Reevaluation of Gulf of Mexico Studies 

Author 

Robert S. Carney 

December 2001 

Prepared under MMS Contract 

14-35-0001-30660-19904 

by 

Louisiana State University 

Baton Rouge, Louisiana 

Published by 

U .S. Department of the Interior Cooperative Agreement 

Minerals 1management Service Coastal Marine Institute 

Gulf of Mexico OCS Region Louisiana State University 

DISCLAIMER 

This report was prepared under contract between the Minerals Management 

Service (MMS) and Louisiana State University . This report has been technically 

reviewed by the MMS and approved for publication . Approval does not signify that the 

contents necessarily reflect the views and policies of the Service, nor does mention of 

trade names or commercial products constitute endorsement or recommendation for use . 

It is, however, exempt from review and compliance with MMS editorial standards. 

REPORT AVAILABILITY 

Extra copies of the report may be obtained from the Public Information Office 

(Mail Stop 5034) at the following address : 

U.S. Department of the Interior 

Minerals Management Service 

Gulf of Mexico OCS Region 

Public Information Office (MS 5034) 

1201 Elmwood Park Boulevard 

New Orleans, Louisiana 70123-2394 

Telephone Number: 1-800-200-GULF or (504) 736-2519 

CITATION 

Suggested citation : 

Carney, R.S . 2001 . Management Applicability of Contemporary Deep-Sea 

Ecology and Reevaluation of Gulf of Mexico Studies. Final Report. OCS 

Study MMS 2001-095 . U.S. Dept. of the Interior Minerals Management 

Service, Gulf of Mexico OCS Region Office, New Orleans, La. 174 pp. 

ABOUT THE COVER 

The four photographic images are symbolic of the low level of understanding 

about the deep ocean ecology that resource managers must contend with. Three images 

show seemingly homogeneous seafloor with some fine-scale bottom topography of 

unknown origin . Hidden within that fine structure, however, is one of the highest species 

diversity on Earth. The upper-right image shows part of a rat-tail fish, but even this wellknown animal is poorly understood. 

iii 

SUMMARY 

Scientific knowledge of the deep ocean is meager when compared to that of 

coastal areas. As a result the Minerals Management Service or any agency charged with 

environmental management in deepwater is placed at a disadvantage with respect to 

developing scientifically sound management strategies . Deepwater management requires 

extensive new data gathering and critical evaluation of the adequacies of existing 

information. A status review of contemporary deep-sea ecology found four areas of basic 

research especially relevant to management. First, the sensitivity of deep fauna to impact 

must be known. Traditional generalities about deep natural histories, however, are being 

discarded, complicating the task of making predictions about sensitivity. Second, the 

deep-sea biota is not uniform from the 200 m upper limit of deepwater to the base of the 

continental slope. The exact nature of faunal gradients must be known to develop depthappropriate monitoring plans and regulations. Third, the processes that maintain a high 

species diversity in the deep-sea must be known if impacts are to be avoided. Fourth, if 

food is truly limited in the deep sea, then interruption of the processes of supply and 

utilization may be the most sensitive process of the ecosystem. 

Past efforts by federal agencies provide relatively little information relevant to 

regulation of deep oil and gas development . Some of these studies focused on human 

health rather than ecology, and others addressed very different impacting activities. The 

studies associated with manganese nodule mining do, however, serve as a useful guide . 

They focused upon detritus foraging; they linked environmental monitoring to large-scale 

industry activity, and they included a mix of federal and industry initiated research . 

Most information about the Gulf of Mexico typical deep-sea benthos was 

provided from two studies, the long-term exploratory sampling of Pequegnat and the 

shorter-term transect sampling of the Northern Gulf of Mexico Continental Slope 

(NGMCS) study. The former focused upon megafauna and proposed zoogeographic 

divisions on the basis of biotic and abiotic data. The latter focused upon macrofauna and 

addressed the validity the zoogeographic patterns through faunal analyses. Lack of 

balance in statistical testing, however, left the validity or invalidity unresolved. On 

reanalysis, three important findings emerged. First, the Gulf slope may have higher 

species richness than found off the US Atlantic coast. The findings however, are 

technique sensitive. Second, diversity is uniformly high with depth, not showing a lower 

slope maximum. This suggests different mechanisms of diversity maintenance in the 

Gulf. Third, the Gulf slope shows a lower biomass than the Atlantic, but the distinction 

decreases with depth. Again, the results are technique sensitive. 

Chemoautotrophic communities represent a distinctive ecosystem of high 

biomass, low species richness, specialized fauna, and partial isolation from the detritusbased food web of the surrounding deep sea. Between 400 and 1000 m in the northern 

Gulf of Mexico the chemoautotrophic and associated heterotrophic species composition 

varies site-to-site . That variation reflects changing combinations of a limited set of 

species. The factors determining each local fauna combination remain unknown. 

Species succession, to the extent that it takes place, may be controlled with a geological 

transition from young, fluid-prone to older mineral-prone seeps. Monitoring of markers 

found no recovery from sampling disturbances . 

v 

TABLE OF CONTENTS 

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 

LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xiii 

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

1 .1 Introduction: Environmental Management of the Deep-Sea Floor . . . . . . . . . . . . . . . . . . . . . 1 

1 .1 .1 Origins of the Wasteland View of the Deep-Sea Ecology . . . . . . . . . . . . . . . .1 

1 .2 Structure of Report . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 

2 A Review of the Management Relevance of Deep-Sea Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

2.1 Physical Properties Characterizing the Deep-Sea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

2.1 .1 Pressure Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

2 .1 .2 Density, Temperature, and Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

2 .1 .3 Darkness and Light as a Defining Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

2 .1 .4 Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

2 .1 .5 Water Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

2.2 Deep Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 

2 .2 .1 Changing Generalities about Deep-Sea Adaptations . . . . . . . . . . . . . . . . . . . . . . . 17 

2 .2 .2 Review of Deep Fauna by Size Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

2 .2 .3 Megafauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 

2 .2 .4 Macrofauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

2 .2 .5 Meiofauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 

2 .2 .6 MMS Management Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

2.3 Zonation - The Depth Gradient As Multiple Habitats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

2 .3 .1 Summary Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

2 .3 .2 State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

2 .3 .3 History of Zonation Concepts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

23 .4 The Analysis and Criteria Problem. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 

2 .3 .5 MMS Information Needs Concerning Zonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

2 .4 Deep Diversity - The Most Confusing Management Concern . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

2 .4 .1 Definitions and Measures of Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 

2 .4 .2 Ideas About Deep-Sea Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

2 .4 .3 Larger Scale Views of Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 

2 .4 .4 MMS Information Needs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 

vii 
2.5 Ecosystem Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

2.5 .1 Biomass and Trophic Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 

2.5 .2 Bioturbation Tracks and Trails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 

2.5 .3 MMS Management Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

2 .6 Case Stud ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

2.6 .1 Introductory Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 

2.6 .2 Deep Ocean Mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 

2.6 .3 Ocean Dumping of Hazardous Wastes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 

2.6 .4 A Flawed Proposal to Scuttle an Oil Storage Facility . . . . . . . . . . . . . . . . . . . . . 56 

2.6 .5 Summary of Lessons Learned . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 

2.7 Deep Survey Design and Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

2.7 .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

2.7 .2 Sampling Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 

2.7 .3 Increased Data Access and Ease of Visualization . . . . . . . . . . . . . . . . . . . . . . . . . . 62 

2.7 .4 Changing Approaches to Statistical Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 

2.7.5 Times Series and Intervention Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 

2.7 .6 The Role of Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 

2.7 .7 Ships, Submersibles, and Other Sampling Platforms . . . . . . . . . . . . . . . . . . . . . . 65 

2.8 Conclusio ns and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 

2.8.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 

2.8 .2 The Physical Deep Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 

2.8 .3 Deep Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 

3 Reanalysis and Synthesis of Gulf of Mexico Deep-Sea Benthic Studies . . . . . . . . . . . . . . . 79 

3 .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 

3 .1 .1 Data Sources for the Gulf and Comparison Studies . . . . . . . . . . . . . . . . . . . . . . . . 79 

3 .2 History of Major Gulf of Mexico Deep Ecological Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 

3 .2 .1 Pequegnat Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 

3 .2 .2 NGMCS Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 

3 .2 .3 Atlantic Continental Slope and Rise: a Comparative Study. . . . . . . . . . . . 91 

3 .2 .4 Problems of Sampling Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 

3 .3 Physical Environment of Northern Gulf of Mexico . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 

3 .4 General Observations About Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

3 .4 .1 NGMCS Natural History Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

3 .4 .2 Megafauna: How Well Known ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 

3 .4 .3 Different Lists of Rare Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 

3 .4 .4 Specific Taxa Considered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 

. 3 .5 Zonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

3 .5 .1 The Zonation Controversy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

3 .5 .2 NGMCS Analyses of Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 

3 .5 .3 Consideration of a Null Model for Restricted Depth Zones. . . . . . . . . . 103 

viii 
3 .6 Geographic Differences Tested by NGMCS ANOVA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 

3 .6 .1 Consideration of an Ideal Case of ANOVA Use . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 

3 .6 .2 ANOVA of Macrofauna in the NGMCS Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 

3 .7 Meiofauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 

3 .7 .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 

3 .7 .2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 

3 .8 Megafauna Trawl and Photo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 

3 .8 .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 

3 .8 .2 Photosurvey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 

3 .8 .3 Megafaunal Biomass: Two Estimates and Possible Special Habitats 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 

3 .9 Macrofauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

3 .9 .1 Macrofauna Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

3 .9 .2 Macofaunal Density Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

3 .10 Conclusions and Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

3 .10.1 Recommendations of Pequegnat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

3 .10.2 Conclusions and Recommendations of the NGMCS Study . . . . . . . . . . 123 

3 .10.3 Conclusions and Recommendations of this Review . . . . . . . . . . . . . . . . . . . . . . 124 

3 .10.4 Recommendations of This Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 

4 Extension of Chemosynthetic Fauna Disturbance Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 

4.1 .1 The Contrast of Two Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 

4.1 .2 Characterization of the Assemblage Across Sites . . . . . . . . . . . . . . . . . . . . . . . . . 130 

4.2 Markers and Recovery Experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

4.2 .1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 

4.2 .2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 

4.2 .3 Results to 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

4.2 .4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 

4.2 .5 Conclusions Limitations and Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 

4.3 Results of Faunal Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 

4.3 .1 Results of Site Cataloguing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 

4.3 .2 Results of Mussel Scoops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 

4.3 .3 Dominant Species in the Upper Slope Seep Assemblage . . . . . . . . . . . . . . 140 

4.4 Causes of Variation in Seep Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 

4.4 .1 The Fault Conduit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 

4.5 Classification of Seep Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 

4.5 .1 Evidence of Episodic Seepage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148 

4.5 .2 Has Faunal Succession Been Seen?. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 

4 .5 .3 Limitations of the Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 

ix 
4.6 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151 

4 .7 General Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 

5 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 

x 
LIST OF FIGURES 

Figure Page 

Figure 2 .1 Salinity at Comparable Latitudes in the NE Pacific, Gulf of 

Mexico, and NW Atlantic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Figure 2 .2 . Temperature at Comparable Latitudes in the NE Pacific, Gulf 

of Mexico, and NW Atlantic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Figure 2 .3 . Oxygen at Comparable Latitudes in the NE Pacific, Gulf of 

Mexico, and NW Atlantic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Figure 3 .1 . Locations of Pequegnat Samples Across Gulf of Mexico and 

Depth Sampling Effort. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 

Figure 3 .2 . Locations of the NGMCS Study Transects and Supplemental 

Stations with Depth Effort of Boxcoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 

Figure 3 .3 . Box Corer and Arrangement of Subcores Employed in 

NGMCS Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 

Figure 3 .4 . Upper Gulf Oxygen Values Obtained from NODC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

Figure 3 .5 . Upper Gulf Oxygen Polynomial Curves Based on Fourth 

Degree Fits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Figure 3 .6 . Megafauna Density Estimates Based on Photosurvey and 

Trawling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 

Figure 3 .7 . Rarefaction Curves Contrasting the Deep Macrofauna with 

Regional Gulf of Mexico Continental Shelf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 

Figure 3 .8 . Sample-level Diversity Trends in the Western Atlantic. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 

Figure 3 .9 . Sample-Level Diversity Trends in NGMCS Study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 

Figure 3 .10. Rarefaction Curves for Gulf and Atlantic Macrofuana. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

Figure 3 .11 . Comparative Depth Decrease of Macrofauna Densities . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 

xi 

LIST OF TABLES 

Table Page 

Table 2 .1 . Physical and Chemical Factors and Their Relevance in Oil and 

Gas Industry Impacts to the Deep Environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Table 2 .2 . Management Utility of Megafuana in Monitoring and 

Background Surveying Contracted to Limits of Utility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

Table 2 .3 . Management Utility and Limitations of Utility of the 

Macrofauna Size Class in Background Surveying and 

Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

Table 2 .4 . Utility and Limits of Utility of the Meiofauna. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 

Table 2 .5 . Depth Zone Names and Applicable Regions Proposed by 

Various Workers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 

Table 2 .6 . IAEA Categorized Criteria for Deep-Sea Nuclear Waste 

Disposal Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 

Table 2.7. Cable Technologies Suitable to Deep Ocean Environmental 

Studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 

Table 2 .8 . At-Sea Cost Basis for Major Activities of Trawling, Box 

Coring, Bottom Surveying, and Moored Instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 

Table 3 .1 . Faunal Criteria for Establishment of Pequegnat Depth Zones . . . . . . . . . . . . . . . . . . . . . . . 84 

Table 3 .2 . Main Depth Series Stations Based on Pequegnat Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 

Table 2.3 . Timing of Sampling of Primary and Auxiliary Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 

Table 3 .4 . Taxa Overlap by Abundance Level in NGMCS and Pequegnat 

Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 

Table 3 .5 . Rank Comparison of Dominant Megafauna in NGMCS and 

Pequegnat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . . . . . 100 

Table 3.6 . Hypotheses and Applicable Samples for ANOVA #1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 

Table 3.7 . Twelve Species Showing Regional Differences and Direction 

of Abundance Differences Within Transacts of ANOVA#1 . . . . . . . . . . . . . . . . . . . . . . . . 107 

Table 3 .8 . Ten ANOVA#2 Depth Contrast Hypotheses Tested on Central 

Transact and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 

Table 3 .9 . Hypotheses, Number of Significant Results, and Stations 

Contrasted in ANOVA # 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 

Table 3 .10. Hypotheses, Type of Question Asked, Number of Significant 

Species, and Samples Contrasted for ANOVA #4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 

Table 3 .11 . Meiofauna Sampling Effort. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- . . . . . . . . . . 111 

xiii 
Table 3 .12. Executed Trawl Sampling Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 

Table 4.1 Geological and Faunal Characteristics of Lease Blocks Studies 

by the Coastal Studies Group. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 

Table 4.2 . Faunal Counts for Major Taxa Contrasted with Results at Other 

Sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 

x1v 
Introduction 

1 .1 Introduction : Environmental Management of the Deep-Sea Floor 

The topics of this report are intended to aid ocean managers, especially the 

Minerals Management Service (MMS), with the task of formulating management 

strategies appropriate for the deep sea environment. This report supplements the broader 

consideration of deep oil and gas development contained in Carney (1998) . Three topics 

are considered : (1) general deep-sea ecological knowledge, (2) regionally specific 

knowledge about the Gulf of Mexico, and (3) hydrocarbon seeps, a special class of deepsea system . The perspective taken in reviewing each topic is the same, and is based upon 

a pragmatic view of the task facing MMS. Oil and gas development has been managed by 

MMS at shelf depths for about 40 years under a strategy based on scientific knowledge of 

that environment. As industry moves into progressively deeper water, MMS must decide 

to what extent the shelf strategy can be applied and how to most effectively obtain 

relevant information about a poorly known environment. In the context of these needs, 

this review attempts to do three things : (1) determine what is known; (2) determine what 

is relevant; and (3) critically evaluate the seemingly relevant information. 

More detailed information is available in the few excellent books on various 

aspects of deep-sea ecology that have been published in the past decade. Most notable 

are the comprehensive review in a textbook format of Gage and Tyler (1996), Deep Sea 

Biology: A Natural History of Organisms at the Deep-sea Floor and the consideration of 

deep fisheries by Merrett and Haedrich (1997) Deep-Sea Demersal Fish and Fisheries. 

Written coherently by just two authors, both are highly comprehensive and useful books. 

Van Dover (2000) has produced an excellent compilation and synthesis of information on 

hydrothermal vents, Ecology of Deep-Sea Hydrothermal Vents. That work provides a 

brief, but very informative discussion of cold seep systems as well . Multiple author 

collections have also appeared. A critical evaluation of ideas concerning reproduction in 

the deep-sea has been compiled by Young and Eckelbarger (1994), Reproduction, Larval 

Biology, and Recruitment of the Deep-sea Benthos. Trophic structure and carbon influx 

has been treated in Deep Sea Food Chains and the Global Carbon Cycle edited by Rowe 

and Pariente (1992) . Unfortunately, there are few contemporary books focusing on the 

major taxa in the deep-sea. A notable exception is the Randall and Farrell (1997) edition 

of Fish Physiology Vol . XVI devoted to deep-sea fishes . 

l . l . l Origins of the Wasteland View of the Deep-Sea Ecology 

In a broad sense, the generic need for deep-ocean management strategies arises 

from two different development plans for the seafloor. To some developers, the deep-sea 

floor is valued land offering resources such as food, hard minerals, and hydrocarbons. To 

others it is inherently valueless, a wasteland providing a socially acceptable repository for 

highly hazardous materials. Until now, the scientific development of deep-ocean 

environmental management has been minimal for practical reasons. Little immediate 

need for management has been seen, since deep-ocean resource plans have been 

futuristic, and most ocean disposal has been banned. Adding to this lack of pressing 
need, the deep ocean is comparatively far removed from human habitation, and coastal 

marine habitats have had a justifiably higher regulatory priority . 

While hard mineral mining, waste dumping, and deep-ocean fisheries remain 

somewhere in the future, oil and gas development is progressing rapidly down the 

continental slope. Thus, the Minerals Management Service (MMS) of the US 

Department of Interior now faces the task of wisely managing development of deep US 

waters. That task is a complex one. MMS must protect a vast poorly known 

environment from unacceptable impact while avoiding unnecessary restriction of an 

industry that is accepting great capital risks in pursuing new technologies . Managers at 

MMS and other regulatory agencies should be prepared to encounter people in industry, 

the general public, and even ocean science who do not feel there is any need for deep 

ocean environmental concern. This assumed lack of regulatory need is due to the deep 

sea's misunderstood status as a wasteland; the last remaining wasteland in some people's 

view. The classification "wasteland" is a time-honored societal judgement. Society has 

always produced waste materials and disposed of them in convenient areas of no 

particular value. Two hundred years ago populations and technology were less waste 

producing, and wastelands were easy to find . There was much undeveloped land and no 

understanding of how watersheds, groundwater, and food chains might interconnect. 

Modern society has virtually run out of terrestrial wastelands, yet, our wastes are more 

abundant and increasingly hazardous. Unfortunately, the deep-sea is seen by some as an 

appropriate waste repository. 

The origins and persistence of the idea that the deep-sea floor is a wasteland with 

little ecology to protect has an interesting history in the oceanographic literature that 

explains the current confusion of some scientists on the matter (Carney 1997). As a 

result of the Challenger Expedition, Murray (1895) enthusiastically reported a highly 

diverse but low-density fauna comprised of many species new to science. Oddly, this 

report had minimal impact on subsequent workers. In a seminal book, Tiergeographie des 

Meeres, Ekman (1935, 1953) chose to force deep-sea observations to conform to the 

"biocoenotic principal" and stressed the low abundance rather than high diversity. It was 

this partial view of deep-sea biology that was incorporated into the first widely used 

oceanography text (Sverdrup, et a1 .1942) . The Oceans remained in use as a graduate text 

into the 1970's misinforming many geological, chemical, and physical oceanographers 

about the deep sea. Even though biological oceanographers are usually taught about the 

rediscovery of high deep-sea diversity (Sanders et a1 .1965) during graduate education, the 

topic is often omitted from marine biology texts and even texts on diversity theory . 

1 .2 Structure of Report 

Chapter two on general deep-sea ecology is organized into eight sections. Where 

appropriate, the sections are written with conclusions given first and details second . 

Section one provides a brief sketch of properties that characterize the deep-sea 

environment and considers which are more likely to be important in environmental 

impacts. Section two reviews deep-sea fauna by taxa and size category. Section three 

reviews information about faunal change with depth. Four considers the complex topic of 

species diversity. Five reviews ecological processes. Six examines past US federal and 

one English program that attempted to develop science-based management of the deep 

2 
environment. Seven reviews current methods of deep-sea study. Section eight provides a 

summary with recommendations. 

Chapter three reviews the long-term sampling of Willis Pequegnat and colleagues 

at Texas A&M and the three year NGMCS study (Northern Gulf of Mexico Continental 

Slope) conducted by LGL Ecological Research Associates Inc. and Texas A&M. Section 

one details the procedures used in the review and the limitations of the available data 

archives . Section two presents an overview of the studies in terms of design, methods, 

and general results. Section three presents an overview of east-west Gulf differences 

focusing on oxygen data. Section four provides an introduction to the fauna collected in 

the Gulf. Since opinions about zonation played a major part in previous Gulf studies, this 

topic is treated separately in section five . Section six critiques and summarizes the 

extensive use of analyses of variance in the NGMCS study . The following three sections 

consider megafauna, macrofauna and meiofauna separately. Section 10 includes 

conclusions and recommendations. 

Chapter four's intent is different from the others in that it seeks to add new 

information to a growing synthesis about hydrocarbon seep communities. It does this in 

three ways. First, it adds additional faunal survey sites to the existing MMS-developed 

geographic inventory. Second, it extends the observation time of recovery experiments 

and monitoring markers. Third, it summarizes a geological-control model of seep 

succession, suggesting incorporation of a gradient-competition component to explain 

natural variation in species composition. 

3 

2 A Review of the Management Relevance of Deep-Sea Ecology 

The ocean waters and bottom beyond the edge of the continental shelf comprise 

the largest and least studied ecosystems. As with any poorly studied system, the number 

of questions about its nature and functions far exceed the number of accepted facts. Even 

for those facts, the limited amount of sampling and the vastness of the environment call 

into question exactly how well established they truly are . Thus, the task of developing 

deep-sea management strategies requires three determinations : (1) what is known; (2) of 

that, what is relevant ; and (3) of that, what is truly valid? 

This review is intended as a start to making those determinations . By design, the 

review is narrowly focuses upon deep-sea benthic ecology. It does, however, begin with 

a brief consideration of the physical environment since the extreme physical factors are 

clearly of great biological importance. Serious omissions of the review are the lack of any 

consideration of the deep pelagic environment and no detailed consideration of the 

sedimentary environment . The deep pelagic environment is even more poorly known 

than the benthos. As the habitat of charismatic species such as sounding sperm whales 

and giant squid, it is a region that can capture the public's imagination . Deep-sea geology 

is a very active field of research, and certain components are highly relevant to an 

ecologically relevant characterization of habitat . However, the task of establishing that 

relevance is substantial and well beyond the scope of the current review. 

2.1 Physical Properties Characterizing the Deep-Sea 

In asking the thematic question, " is there scientific evidence strongly indicating 

that shallow-derived management strategies can not be applied to deepwater", it is 

appropriate to begin by examining the non-biological aspects that set shallow apart from 

deep. To do this, it is necessary to decide where the deep sea begins . Ocean 

geomorphology provides the basis for a legal definition of deep sea, beginning at the 

break of the continental shelf. For the purposes of the Law of the Sea, the United Nations 

set this at 300 fathoms (Guilcher et al . 1957), an isobath selected to include the deepest 

breaks . For oil and gas regulation, the depth may be taken as 200 m which coincides 

with the shelf break in the Gulf of Mexico and is used in the Deepwater Oil and Gas 

Royalty Relief Act. 

When the deep ocean is defined as that zone lying below 200 m, it is obvious that 

this is not a physically homogenous environment. The uniformity of physical 

characteristics typically associated with deepwater ecology starts deeper at approximately 

1000 m. Thus, management may need to consider the 200 to 1000 m zone (the upper 

continental slope) a separate zone of environment transitions. It is in this zone where 

sunlight effectively vanishes, where temperatures and salinity become stable through the 

seasons, and where oxygen drops to a minimum value. The interaction of physical 

processes and potentially impacting oil and gas activities may be different in this 

transition zone than deeper . A summary of concerns appropriate for this transition zone 

and the rest of the deep environment is presented in tabular form (Table 2 .1). 

Discussions of these points are presented in the following subsections. 

5 
2.1 .1 Pressure Effects 

It is well established that there are major biological effects of hydrostatic 

pressure . Hydrostatic pressure is a function of depth and the density of seawater. with 

exact pressure described by the seawater equation of state and depth. For ecological 

purposes, density variations can be ignored and pressure considered to increase one 

atmosphere for every ten meters of depth. 

Pressure causes some simple physical-chemical changes. First, water is slightly 

compressible (about 1 % decrease in volume at 3500 m depth) . Therefore, pressure alters 

volume concentration of solutes, makes water slightly more acidic, and raises the 

temperature (adiabatic heating) slightly . These physical effects are treated in any 

advanced physical oceanography text such as Apel (1987) . Second, pressure influences 

the rates of chemical reactions including dissolution and dissociation . While the theory 

behind these effects is simple, it has little predictive value, and the actual effects must be 

measured experimentally . The theoretical basis for pressure effects lies in volume 

change. If a chemical reaction produces an increase in volume, pressure will oppose that 

reaction. If there is a volume reduction, pressure will promote that reaction. This model 

is marginally adequate for inorganic chemical reactions. Organic reactions, which are 

stereospecific, may be more sensitive to pressure then volume changes predict. 

There are three pressure effects that may be most important in deep-sea ecology: 

enzyme reaction rates, the solubility of calcium carbonate, and the stability of gas 

hydrates. 

" Solubility of Calcium Carbonate - It has long be noted that abyssal sediments 

below approximately 4000 m lack the abundant calcium carbonate tests of 

foraminifera that give sand-sized grain structure to bathyal and upper abyssal 

muds (Biscaye et al . 1976) . This depth distribution was formally explained 

in terms of the calcite compensation depth, CCD, a depth at which the 

dissolution of sinking tests equals the rate at which the material accumulates. 

Above the CCD carbonates accumulate in the sediment, while below they do 

not. The sharp vertical demarcation suggests that the solubility of carbonate 

must undergo a rapid increase over a relatively narrow depth range, termed 

the lysocline. The lysocline is primarily the consequence of pressure and pH 

influencing dissolution (Archer 1991) . Since respiration and water mass age 

influence pH, the lysocline is deeper in the older Pacific water than the 

Atlantic . The lysocline varies in depth throughout the ocean. In the North 

Atlantic, it lies at about 4000 m depth. Due to the relative shallowness of the 

Gulf of Mexico, the phenomenon has been poorly studied there. There are 

two management-relevant aspects of pressure effects upon calcium carbonate 

dissolution. First, differences in sediment texture above and below the CCD 

may cause ecological differences. Second, shallow-water models for fates 

and effects of carbonate containing discharges can note be applied in or 

below the lysocline. 

" Clathrate Hydrate Stability - Clathrate hydrates are solids consisting of a water 

molecule cage trapping a low molecular weight hydrocarbon, typically 

methane. They are associated with chemosynthetic communities, and in 

some settings may be a prerequisite for their existence (Carney 1994). They 

6 
are found in deep-sea sediments where there is an adequate supply of 

methane, sufficient pressure, and low enough temperature to allow stability. 

The clathrate stability envelope is defined by the material's liquid-gas-solid 

phase diagram. At a depth of approximately SOOm, the ocean is typically 

6 .0 C and clathrates can exist. At lower pressures and higher temperatures 

they are not stable . Due to geothermal heat, clathrates can not exist at depth 

in sediments. Sloan (1989) has treated clathrates in a comprehensive manner. 

Although recognized as a geological feature of the deep-sea floor in the 

1970's (see summary by Kvenvolden, 1988), they have recently become the 

source of intense interest due to Japanese plans to exploit them. It is possible 

that at some point, MMS may be required to regulate clathrate development 

within the US EEZ. From an ecological perspective, they may constitute a 

special habitat. 

2.1 .2 Density, Temperature, and Salinity 

The permanent pycnocline (density gradient) is an ecologically relevant physical 

feature dividing the shallow ocean from the deep. In offshore regions remote from 

freshwater input, density is primarily determined by water temperature . The permanent 

pycnocline and the related thermocline are that depth zone where downward flow of solar 

heat is relatively unaffected by seasonal fluctuations . This region is in contrast with the 

overlying seasonal thermocline where the density and temperature profiles vary through 

the year. Since heat input and ocean mixing vary over the Earth, the depth and exact 

density or temperature range of the respective permanent pycnocline and thermocline 

also vary. 

For many years, the global compilation of deepwater physical data prepared by 

Mantyla and Reid (1983) has been the basis of descriptions of the permanent thermocline. 

This sparse and edited data presented oceanographers with a false image of a relatively 

fixed boundary. During this review, the National Oceanographic Data Center provided 

access to experimental search engines under development at Scripps Institute of 

Oceanography. All archived surface to bottom hydrocasts for the Gulf of Mexico were 

obtained along with comparable data for the coast of California (MMS Pacific Region) 

and the US east coast south of the Carolinas (MMS Atlantic Region). The scatter plots of 

these data provide a much more dynamic picture of a fluctuating thermocline (Figures 

2.1, 2.2, and 2 .3). The main ecological consequence is that fauna between 500 m and 

1000 m in the Atlantic and Gulf of Mexico will experience temperature fluctuations 

associated with vertical pycnocline movement. The same depths in the Pacific will be 

much more stable . 

The water density, temperature and salinity on the deep-sea floor are controlled 

by the density stratification of the overlying water mass. Temperatures (Figure 2.1) range 

from about 10°C at the top of the deep zone (200m) to 2°C (>3000m) except in silled 

basins . The Gulf of Mexico is such a Billed basin connecting with the deep circulation of 

the Atlantic through a 1600 m deep sill in the Straits of Yucatan. This sill blocks the 

coldest water flow making the Gulf of Mexico isothermal at about 4°C below that depth 

(ignoring adiabatic heating) . The salinity (Figure 2.2) of the deep-sea bottom shows little 

departure from 35 PSU (Practical Salinity Units) . 

7 
Table 2.1 . Physical and Chemical Factors and Their Relevance in Oil and Gas Industry 

Impacts to the Deep Environment. 

Property Natural Condition & Oil & Gas Activity Impact Concern 

Effects 

Pressure Increases uniformly with depth as the 1 . Industry activity can not modify pressure, 

sum of the weight of overlying however: 

water, approx. 1 atmosphere 2 . Solution chemistry of discharges may be 

(1 atm) for every 10 m. affected by pressure, making shallow 

Alters some inorganic and water knowledge inapplicable . 

biochemical reaction rates and 3 . Gas hydrates pose a known hazard and an 

decreases pH . unknown special habitat. 

Alters solubility of carbonates . 

Increases density, viscosity, and 

temperature of water. 

Density Changes non-uniformly with greatest 1 . Unlikely that industry activity can modify 

(Salinity & change at permanent pycnocline. density fields, however: 

Temperature) Is transitional from 200 to 1000 2 . Limited stratification in deep water will 

m then becomes uniform and allow discharge plumes to easily 

high in cold deep bottom water propagate 

(when minimal pressure effects 3 . Stratification in deep Gulf of Mexico is 

are ignored) even less understood than in open ocean 

due to sill depths. 

Light Sunlight decreases exponentially with 1 . Industry activity can cause deep plumes of 

depth. Is present but low low transmission water. 

intensity in a transition zone 2. Sunlight is still present in the 200-1000 m 

below 200 m and is generally range and animals may be especially 

thought of as absent deeper than adapted to low light and be especially 

1000 m. Bioluminescence subject to increased turbidity. 

important in behavior of deep 3. Below sensible sunlight, biological light 

animals. plays a major role in animal interactions. 

Increased turbidity may impact such 

interactions . 

Oxygen Dissolved oxygen distribution reflects 1 . Through injection (spills) of labile carbon, 

upper ocean stratification and industry activity may alter local balance 

has a minimum at 500 m of oxygen consumption and replacement. 

influenced by the balance of This is most likely to be of concern in 

local oxygen consumption and smaller Billed basins where hypoxia or 

horizontal advection of oxygen anoxia may result . 

rich deep water. Below 1000 m 

oxygen is again high and 

relatively constant. 

Water Stratified upper ocean inhibits 1 . Industry activities can not alter major 

Movement downward propagation of current flows, however: 

currents . Deep bottom 2. Bottom structures and topographic 

characterized as low energy low modification will impact BBL 

tidal, geostrophic, and conditions . 

thermohaline currents ; episodes 3. Prediction of plumes, distal impacts, etc. 

of high current velocity do occur. must consider both prevailing and 

episodic flows. 
Deep-ocean management must view the pycnocline as a very important ecological 

boundary in the ocean. With respect to plume models and chemical effects of discharges, 

density stratification limits vertical movement in the ocean of heat, momentum, and 

solutes. Therefore, processes below the permanent pycnocline are somewhat isolated 

from the upper ocean. Physiologically, temperature is very important in controlling 

distributions. The transition from the cold deep ocean to the warmer shallow ocean is 

considered a major physiological boundary . On the sea floor of the Gulf of Mexico, the 

thermal gradient between 200 and 1600 m is equal to the continental shelf from Nova 

Scotia to the Florida Keys. 

2.1 .3 Darkness and Light as a Defining Features 

Since darkness is usually considered a primary characteristic of the deep-sea, it 

might seem that environmental management of deepwater does not need to be concerned 

with light. However, this would be incorrect since light is important in the deep sea in 

two senses . First, ambient sunlight may be sufficient even at 1000 m to be used as a 

sensory cue by sighted organisms. Second, at depths where the ambient sunlight is of no 

sensory value, the optical properties of water will determine how well bioluminescent 

light can be perceived. Therefore, manmade alternation in the optical properties of water, 

especially increases in turbidity may have profound effects. 

The importance of light in the deep sea and the potential for light-associated 

environmental impact can be shown from a simple treatment of light in the sea. Once 

light has entered the sea, it is either absorbed or scattered back upward. Scattering and 

absorption combined are termed attenuation. Attenuation is such that light intensity 

decreases exponentially with depth . There is color-specific absorption such that in clear 

oceanic water a wavelength of 462 nm has maximal penetration. Defining the bottom of 

the euphotic zone as 1 % of surface illumination, this may be found at about 100 m. 

However, below this depth there is ample light for human vision . At 500 m in clear 

water, the ambient sunlight is about one millionth that of the surface. 

Sighted animals on land and in the ocean use ambient light to sense where things 

are in the environment and to take action based upon such knowledge. These actions 

include such vitally important activities as locating food, avoiding predators, and finding 

mates. Due to the great importance of these vision-dependant activities, alteration of the 

ambient light field in water, usually an increase in turbidity, can be the cause of impact . 

The field of sunlight at any depth may be approximated by the equation: 

IZ=Ip -kz e 

Where Io is the intensity just below the ocean surface; IZ is the intensity at depth z, 

and k is the diffuse attenuation coefficient with the unit's m"' . Diffuse attenuation is the 

sum of absorption and scattering . It is termed an "apparent" property since it is 

dependent upon the illumination . A related "intrinsic" optical property of water is beam 

attenuation. In clearest waters the minimum diffuse attenuation (k=0.0168) is for blue 

green light (wavelength 450 nm). We know that k varies greatly with wavelength and 

ocean particulate matter; in coastal waters it can have values higher than 0.25 . However 

in deep oceanic waters, it is relatively low and uniform, around 0.03 to 0.04 (Jerov 1976). 

9 
0 

1000 

2000 

D 

E 3000 

P 

T 

H 

4000 

F~ . 

rid ; 

w. 4: 

.Y. 

.. 

r 

PAC 

S. - GULF ATL 

NE ALL 

.; 

NW 

33 35 33 35 

Sz>1500 = 34.637 SZ,1500 = 34 .975 SZ,1500 = 34 .952 

±0.046 10.083 10.039 

n=149 n=835 n=282 

SALINITY, PSU w/ scales offset 

Figure 2.1 Salinity at Comparable Latitudes in the NE Pacific, Gulf of Mexico, and 

NW Atlantic. Averages based on data below 1500 m. 

10 
0 

1000 

D 

E 

p 2000 

T 

H 

- 

- ~ . 

' RR 

~+= -

approx. _ 

Sill Depth ~ 

PAC { GULF ATL 

NE ~ ALL NW 

i ~ - 

I ~ I L I l ` I 

-0 : 10 0 ~ 10 0' 10 

Tmin = a .o7o° 

Tmin = 1 .490° 

Tmin =2.177° 

Temperature, Degrees Celcius 

Figure 2.2 . Temperature at Comparable Latitudes in the NE Pacific, Gulf of Mexico, 

and NW Atlantic . Averages based on data below 1500 m. 

3000 

4000 

5000 

11 
0 

1000 

I 

LL 

2000 

3000 

4000 

t 

k 

1 . 

'.1 

PAC 

'`. NE 

I 

0 5 

at) 

Oz= 2.074 Oz= 4.915 

n = 154 n = 447 

Dissolved Oxygen MI/L 

Figure 2 .3 . Oxygen at Comparable Latitudes in the NE Pacific, Gulf of Mexico, 

and NW Atlantic . Averages based on data below 1500m. 

12 

0 5 

t 

Oz= 6.056 

n =282 
Theoretically, there is some sunlight thousands of meters deep in the ocean. 

Darkness is not a physical condition, but a neurosensory one. The degree of darkness is 

determined by the sensory system of the viewer . At some depth the level of light is so 

low that falls below the limits of detection or is swamped by neurological noise. On a 

brightly-lit day in clear ocean water an observer in a deep submersible can perceive dark 

shapes in the water at depths between 500 and 520 m. The highly dark-adapted eyes of 

deep-sea fishes may, however, still be sensing ambient sunlight as deep as 1000 m. In 

spite of very low ambient sunlight levels, many deep-sea animals have very well 

developed eyes and must make some sensory use of bioluminescence. Unlike ambient 

sunlight, bioluminescence is a controlled light flash that probably provides some 

information about the individual transmitting the signal rather than the general 

environment. If so, the perception and neurological processing of these light signals may 

be fundamentally different than that association with vision in a lighted field. 

Whatever the usage of bioluminescence, changes in the optical properties of water 

pose a threat to normal ecological functions . Bioluminescent light from an organism can 

be treated as a point source that spreads out as a sphere and undergoes inverse square 

decrease in intensity as well as exponential attenuation. This can be shown by the 

equation 

ID=IoekDD-z 

Where ID is light intensity at some distance D and Io is the intensity at the source . 

In clear ocean water (attenuation, k=0.04) the decrease in light away from a point source 

is far more dependent on distance between source and viewer than minor fluctuations in 

attenuation. However, if turbidity substantially alters k, the distance at which 

bioluminescent signals can be detected drops dramatically . 

2 .1 .4 Oxygen 

The restriction on downward movement of solvents imposed by the two-layered 

ocean has a profound influence upon oxygen distribution in the form of an oxygen 

minimum. Oxygen enters the ocean from the atmosphere and photosynthesis . In the 

upper ocean it may be near saturation at the surface with values of about 5 ml/L in the 

Gulf of Mexico . As dissolved oxygen moves downward, it is biologically consumed by 

respiration faster than it is replenished, producing a low of about 2.5 ml/L at about 500 m 

depth. The depth range of low values (< 3 ml/L) lies between 200 m and 750 m in the 

Gulf of Mexico . The increase in oxygen below 500 m reflects the importance of a second 

oxygen input, long-distance advection of deepwater. At these depths (1000 - 3500 m) 

oxygen returns to values similar to those of the surface (about 5.0 ml/L). The picture of 

the oxygen minimum that emerges from the NODC archives (Figure 2.3) is variable place 

to place. It is more pronounced ( 1 ml/L) and fixed with depth in the Pacific . The 

vertical movement of the thermocline in the Gulf and Atlantic make it more variable at 

any given depth. 

13 
As a result of the oxygen minimum, the benthic environment at that depth is 

inherently hypoxic (Diaz and Rosenberg 1995). Therefore, management is obligated to 

treat the low oxygen zone differently than the well-oxygenated regions above (<200-300 

m) below (>750 m) maximum depth. Care must be taken that operational and accidental 

discharges do not result in greatly enhanced biological oxygen demand. Otherwise, 

bacterial oxidation of spilled hydrocarbons and organic drilling fluids could result in local 

deep anoxia . It also becomes important to know the actual advection rates of oxygen into 

the deep environment and natural biological consumption rates in order to predict the 

impact of discharges . 

2.1 .5 Water Movement 

The buoyancy of warm seawater restricts the propagation of kinetic energy 

downward. This can be seen for both waves and currents. In the case of waves, 

buoyancy opposes the oscillating movement of higher and lower density water up and 

down. This opposition, which can be stated as a stability, buoyancy, or Brunt-Vaisala 

frequency, is a function of the density-depth gradient and is greatest in the top 200 m of 

the ocean. It is noteworthy, however, that once the comparatively uniform densities of 

the bathyal and abyssal depths are reached, there is little buoyant opposition to the 

transfer of any energy. 

When wind drags across the surface of the ocean, it transfers kinetic energy to the 

ocean surface. The surface layer of moving water then drags over the next deeper layer, 

and so on with increasing depth. However water is a deformable, viscous fluid, and only 

a fraction of the velocity at each layer is imparted to the next. Thus, there is an 

exponential decrease in velocity with depth. The layer over which this velocity transfer 

takes place is the surface Ekman layer, and it has typical thickness of less than 100 m. 

Thus, wind driven currents do not typically progress into the deep-sea. The same 

exponential decrease is seen in wave-induced water velocities . The orbital velocity of 

water under a wave decreases exponentially with depth as a function of wavelength . 

Only very long-period waves and tides will have a major effect upon flow in deep water. 

Benthic "Storms" 

Although most of the deep-sea floor experiences currents of about 1-2 cm-s-.1 . 

velocities as high as 50 cm-s-' have been encountered. The presence of episodic high 

velocities was first suspected by geologists who found scour marks and ripples on deep 

bottoms where the observed currents were not capable of the necessary erosion (Heezen 

and Hollister 1971). One mechanism for such elevated current velocities was contour 

currents along an ocean's western margin (Heezen et al . 1966). The term contourite has 

been given to the characteristic sculpted bottom. A comprehensive study of a deep 

bottom experiencing high current velocities was supported by the Office of Naval 

Research (Hollister et al . 1984, Hollister and McCave 1984). The HEBBLE project 

(High Energy Benthic Boundary Layer Experiment) found that in addition to contour 

currents, hurricane passage had a marked influence of flow even below 3000 m 

(Weatherly and Kelley 1985) . As might be expected from an area of bottom erosion, the 

fauna was distinctive (Thistle et al . 1985). 

14 
The Benthic Boundary Layer 

Biologists are generally aware of the importance of velocity gradients as fluids 

(air and water) flow over and within organisms. Vogel (1994) treats the subject 

extensively. Boundary layers (gradients of decreasing velocity approaching a fixed 

surface), are a flow phenomenon found on many scales, including the very large scale of 

current flow over the bottom of the deep sea. A major addition to how ecologists view the 

deep benthic environment was recognition of the importance of the benthic boundary 

layer (BBL). In the 1970's and 80's geochemists, geologists, and biological 

oceanographers became increasingly aware that many properties of the benthos are 

controlled by the physical dynamics of the BBL (Armi and Millard 1976, Wimbush and 

Munk 1970, Richards 1990, Ludwick and Demura 1982) . Here bottom friction between 

currents and the seafloor produce vertical shear that generates near-bottom turbulence . 

This turbulent layer is marked by homogenous properties such as salinity, temperature 

and suspended solids . Simple models (Artni and Millard 1976) have proven inadequate 

at describing the BBL since it varies in thickness between 5 and 100 m (Weatherly and 

Martin 1978) rather than the few meters predicted and does not have a simple relationship 

with current velocity . 

The importance of the BBL in both a management and a basic research context is 

the deep-sea floor is not a completely open or arbitrarily defined system. It has, in effect, 

a ceiling at which exchange of water column properties are limited. The benthos and the 

BBL's pelagic fauna form a unit distinct from the ocean above the BBL. The increased 

suspended material in the BBL may afford improved foraging, such that predators and 

scavengers are likely to restrict their hunting to the BBL, and chemical plumes released 

from the deep bottom may be trapped in the BBL and not diluted through the entire water 

column as some models assume. 

Ecologically, the particle rich BBL (sometimes called a benthic nepheloid layer) 

is not a static suspension. It is an equilibrium feature (Biscaye and Eittreim 1977) of 

particles moving down under the influence of gravity and up due to turbulence ( Ludwick 

and Demura 1982). This is where recently arrived labile detritus resides before final 

deposition. Smith and his associates (see Smith 1987) found that fully 10% of benthic 

carbon consumption actually takes place in the BBL, and Wishner (1980) has established 

that it is faunally distinct from the larger pelagic environment . The management 

implication of the physical and ecological aspects of the BBL is that the deep benthos 

includes more than the surficial sediments . The bottom and the overlying 100 m of water 

form a unified system and should be studied as such. 

2.2 Deep Fauna 

This section provides a brief review of deep ocean fauna in terms of generalities 

and then by the size classes employed in ocean studies. The intent is to aid managers in 

looking at the fauna from four necessary perspectives . There are no differences between 

the perspectives needed in shallow or deep management. However, the relative 

importance to management decisions differ. 

15 
Ecological Importance - In theory, environmental management should be based 

upon an understanding of the roles that each species plays. Maximum 

protection can then be allocated to the most important and most sensitive 

species. In practice, non-fisheries marine management is habitat rather than 

species directed, because it is far easier to delineate a few habitats than to 

assess ecological importance of many species . The deep resource manager 

must consider whether species-level ecological importance can be assessed or 

whether a habitat approach must be used. It is to be expected that the cost of 

gaining information on ecological roles will be very high. 

Potential Resource Conflict - In shallow water, many species have a resource 

value either directly as a fishery or indirectly as an aesthetic component of 

the habitat. While these issues do apply to the deep ocean, it is to be 

expected that fewer resource conflicts will exist. 

Public Perception - Decisions concerning resource management are never based 

only on scientific evidence . While the general public has no direct exposure 

to the deep sea, it is erroneous to expect a lack of interest. The very high 

diversity of the deep benthos, the large number of new species which any 

study will encounter, and the exotic morphologies of a few species appeal to 

the imagination . 

Indicators - Faunal inventories are the main source of information about natural 

and impacted conditions . Therefore, management has an obligation to design 

surveys, monitoring, and experiments so as to be maximally informative and 

cost effective. The low level of knowledge about the deep fauna and the high 

number of new species to be encountered will make this difficult. Identifying 

and focusing on a limited number of indicator species may be the most cost 

effective strategy . 

In development of deep-ocean management strategies, two key aspects of deep 

fauna are outstanding, uniqueness and ignorance . On analysis, the latter poses more 

difficulty than the former. Shallow-water resource managers routinely deal with regional 

uniqueness since marine fauna often changes dramatically from one coastal region to 

another. The northeast continental shelf has a fauna distinct from the southeast and Gulf 

of Mexico; the Florida Gulf coast is faunistically different that the Louisiana coast; the 

fauna off Southern California is distinct from that off the Pacific coast of Alaska; and the 

fauna of the Alaskan Arctic coast is also distinctive. Region-specific and habitat-specific 

management strategies can be developed with relative ease since there usually is an 

extensive pre-existing information base. Typically, such information has accumulated 

independent of the environmental issues over many decades of basic marine biology and 

fisheries research . In shallow water, management must seek out, synthesize, and apply 

this basic information, but it is seldom necessary to undertake information-adding basic 

research . 

The usually implicit and always critical management assumption that adequate 

basic information exists is definitely invalid in the deep sea. The information about deepsea fauna is exceedingly limited. For the vast majority of deep-sea species, we do not 

know such basic information as feeding type, mode of reproduction, life span, predators, 

and population . Therefore, management must take one of two possible courses. First and 

most costly, management must undertake information-gaining research at a much more 

16 
extensive level. Second, the precautionary principal must be applied and regulations 

based upon unproven worst case scenarios. 

2.2 .1 Changing Generalities about Deep-Sea Adaptations 

Are deep-sea animals different than shallow in being inherently more susceptible 

to environmental impact? Can it be inferred that uniformity of some physical features 

has produced species requiring a narrow range of conditions that may be easily upset? 

Or, does the existence of some environmental variability mean that individuals and 

populations will be relatively robust when exposed to human perturbations? Presently 

there are no convincing answers. However, until research directly examines 

susceptibility, it is reasonable for management to turn to published generalities about 

deep-sea adaptation when taking a "first cut" at an answer. This section reviews the 

current status about the most frequently mentioned generalities and considers whether 

there is obvious management relevance . 

In making the critical assessment that a particular generality is valid and relevant, 

it must be appreciated that scientific generalization is influenced by three important 

factors, actual evidence, prevailing paradigms, and fashions of science. When evidence 

is limited, as is the case in the deep sea, paradigm and fashion may be the primary 

influences. For example, from the 1880's to the 1980's the deep sea has been viewed as a 

cold and stable environment. Accordingly, the scientists of that era explained their scant 

evidence of biological and ecological adaptation in terms of the prevailing ideas about 

such environments . It was also the scientific fashion during this period to selectively 

reinforce existing ideas rather than challenge them . Today, we know that there are 

sources of variation in the deep ocean, we have a bit more data about the animals, and the 

scientific fashion is to replace old ideas with new. New generalizations or old, 

management must be cautious when accepting and applying general statements about the 

deep sea. 

The era of early deep-sea exploration coincided with a phase in ecological and 

evolutionary studies where a strong effort was made to explain patterns in nature 

according to deterministic laws and rules such as Cope's Law on size (could 1977) or 

Thorson's Rule on reproductive mode (Thorson 1950) . While the literature contains no 

such law or rule derived from deep-sea observations, generalities about deep-sea fauna 

published as late as the 1960's very much reflected this trend of forcing observations into 

narrow interpretations. This section identifies those generalities that are most likely to 

bear upon management decisions, then briefly discusses others . 

Valid Generalities of Obvious Management Consequence 

There are two related generalities about deep species animal-sediment adaptations 

that seem to be valid for most of the fauna and have immediate management relevance. 

The consequence of both is that alteration of the soft bottom system (particle input, 

sediment-water interface dynamics, etc.) should be of higher concern in deep water than 

in shallow. The shallow-water management strategy of recognizing special habitats on 

the basis of gross substrate differences (hard versus soft) will be insufficient in the deep 

environment where important but subtle habitat variation may occur over the vast soft 

bottom . 

17 
Predominance of Soft Bottom Dwelling Organisms - It has been recognized since 

the Challenger Expedition that the deep-sea floor is overwhelmingly soft bottom. 

Exposed hard bottom habitat is limited to mid ocean ridges and geochemically unique 

environments with authigenic substrate precipitation ( hydrothermal venting, cold 

seepage, and mid-ocean nodule fields, etc.) . Consequentially, the great majority of deepsea benthic species are adapted to soft bottoms. The importance in habitat structuring of 

even small bits of hard substrate, such as a shell fragment, may be greatly increased 

compared to shallow water. 

Predominance of Deposit Feeding - In shallow water, soft bottoms support dense 

populations of deposit feeders, suspension feeders, and animals capable of switching 

between the two modes of feeding. However, in the deep-sea the average influx of 

suspended labile detritus appears to be insufficient to support suspension feeding, 

resulting in a fauna heavily dominated by deposit feeders . There is some initial evidence 

to suggest that microphagy (selection and ingestion of small particles) predominates. 

Suspension feeders are not, however, completely absent . Where suspension feeders are 

found in deep water, it can be assumed that special habitat conditions prevail that 

effectively increase the local flux of organic detritus . 

Less Well Established Generalities of Possible Management Relevance 

Three generalities about the reproduction, morphological and sensory adaptation 

of deep-sea animals are certainly valid for some species and some deep-sea regions, but 

the number of exceptions are so many that extent of applicability remains unestablished. 

Reproductively Distinct - Larval brooding, as exemplified by pericarid 

crustaceas, was once thought to predominate in many deep-sea taxa, giving the fauna a 

unique characteristic. Until recently, few people would have challenged the idea that 

deep-sea animals are reproductively distinctive (Grassle and Sanders 1973) in terms of 

non-seasonal breeding, brooding, direct development, and low fecundity. Indeed, the 

accepted reproductive scenario indicated a fauna highly susceptible to impact . Now, the 

question is in doubt. The topic of reproductive patterns in the deep-sea fauna has 

undergone an excellent critical review (Young and Eckelbarger 1994). The lead 

contribution (Young 1994) and following papers convincingly dispose of the long-held 

generalizations that deep-sea animals conform to Orton's Rule (continuous reproduction 

in a non-seasonal environment) and Thorson's Rule (brooding must be the predominant 

reproductive strategy in an environment lacking a plankton rich pelagic component). 

Rather than having restricted reproductive patterns, deep fauna (such as molluscs) show 

as much adaptive variation as encountered in shallow water. This adaptive range is 

exemplified by measured fecundities ranging from 20 to more than 30,000 eggs per brood 

(Scheltema 1994). Depending upon the species examined, a full range of periodicity is 

encountered from continuous to seasonal (Tyler et a1 .1994) . Surveys of size frequency 

within deep benthic populations also show a range of recruitment patterns rather than a 

single predominant mode. 

Deed Species Differ in Size from Shallow - It has been proposed that deep-sea 

animals differ in size from those in shallow water. A few deep-sea taxa of pericarid 

crustaceans (isopods and amphipods) are comparative giants at lengths up to 38 cm. 

Such gigantism seems to be limited to a few taxa. The case of smaller seems to be better 

18 
established (Thiel 1975). Especially on the very food poor central seafloors, taxa 

normally associated with the macrofauna size fraction are in the smaller meiofauna 

fraction . This size shift is seen as reflecting adaptation to low food levels . The presence 

of unusually large animals is of peripheral management relevance; although "giants" are 

of considerable public interest. A general shift to smaller size underscores the need to 

consider impacts that might alter the food delivery system and argues for the inclusion of 

meiofauna in any comprehensive survey or monitoring. 

Deep Species are Dark Adapted - This generality would seem to be quite self 

evident, but dark adaptation is a complex topic with unexpected management 

consequences. There are two apparently conflicting light-related aspects of deep-sea 

fauna. The first is body color. Deep animals are typically drab (black, gray, white, etc .) 

and patternless even when colored ( bright red organisms are functionally black) . 

However, many deep animals have well developed eyes although some are eyeless. It 

must be concluded that in the deep-sea, light produced by bioluminescence or as residual 

low-level solar illumination is still important. Therefore, environmental management 

must consider those activities that increase turbidity. 

Valid Generalities of Uncertain Management Relevance 

Pressure Adaptation - Hydrostatic pressure has effects on organisms that are more 

dramatic than would be expected from simple physical-chemical consideration of 

reaction product volumes . Aside from gross deformation of gas-filled voids, pressure 

alters many metabolic processes. Pressure adaptation's direct management implication is 

that it makes it exceedingly difficult to carryout sensitivity testing of species with a 

traditional bioassay. Maintaining assay populations under pressure will be very difficult. 

The most recent review of pressure adaptations is that of Gibbs (1997) focusing on deep 

fish enzyme systems. Siebenaller (1991) and Somero et al . (1991) have reviewed 

enzyme-level pressure adaptations and their possible consequences in zoogeography and 

ecology. Siebenaller (1991) has given a succinct and brief summary. Pressure influences 

enzyme function via volume change and membrane function by altering the degree of 

ordering in lipid sheets . Working with congeneric demersal fishes and select enzyme 

systems, it was found that species occupying broad depth ranges had evolved pressure 

insensitive enzymes rather than a suite of depth-specific isozymes in genetically distinct 

sub populations. Working with gills Gibbs and Somero (1990) had suggested that 

function varied enough with a 200 atmospheres pressure change, that adaptations would 

be needed in any species spanning a 2000 m depth range. Siebenaller proposes that there 

is a distinct depth dichotomy of pressure adaptations of cytosolic enzymes . Species 

commonly occurring deeper than 500-600 meters (50-60 atms) have pressure-adapted 

(insensitive) enzymes. Species common above 300 m tend to have pressure-sensitive 

enzymes. This physiological/molecular distinction might serve as on indication of an 

ecological zonation between shallow and deep. 

There has been a change in the focus of pressure studies over the past thirty years. 

Initially, pressure aquaria (Brauer 1972) were used for species-level research to test 

whole organisms. Frequently, testing was done on species found in shallow water 

(Menzies et a1 .1972), and inability to survive under pressure observed. From our current 

management perspective with the need for species-level information, it is unfortunate that 

19 
small pressure cells have replaced pressure aquaria, and whole animals replaced by 

isolated purified enzymes. 

Invalid Generalities of Historical Interest 

Evolutionary Antiquity - Any ocean manager faced with funding deep research 

must be amused by elementary oceanography texts' explanation of the four year voyage 

of the HMS Challenger. We are usually told that the cruise was an effort to test Forbes' 

conjecture that the ocean would be azoic below 600 fathoms. What government agency 

would employ a large ship and scientific party in a long around the world cruise to test a 

hypothesis that required only a few days at sea off the English coast? There was 

obviously much more involved. At the time of the Challenger expedition there was 

widespread curiosity as to what the fauna of the vast, possibly unchanging, and fully 

connected deep ocean might be in evolutionary and zoogeographic terms. It was an era 

when the Darwin-Wallace theory of evolution was fully accepted and intellectually fresh. 

Documentation of geographic species patterns was seen as the primary tool of 

evolutionary studies, and it was well understood that climatic and geological changes 

brought about speciation. Would the deep-sea have a fauna that had escaped such 

influences and remained primitive? 

As a general statement, the deep-sea fauna is not primitive in the sense of being 

populated by living fossils. To a certain extent, however, many deep-sea taxa can be 

considered primitive. This primitiveness is especially notable for the protobranch 

mollusc and the pericarid crustaceans. The only management relevance of the partially 

discredited depth-antiquity relationship lies in public misunderstanding . The statement 

that the deep sea is a refuge for ancient animals, when taken as an unqualified truth, 

inappropriately elevates the importance of that environment. 

2.2 .2 Review of Deep Fauna by Size Group 

While terrestrial ecosystems and the very shallow parts of the ocean have a 

tradition of taxa-specific investigations (i .e . studies of fish, or molluscs, or echinoderms, 

etc.), studies of the deep sea are usually so restricted by sampling equipment that size 

classes are the main focus of inquiry. These classes vary a bit in exact definition, but 

have assumed certain standards in the surveys supported by the MMS. Megafauna are 

those animals that are retained in trawls and can be seen in videos and photographs; an 

approximate size limit is one centimeter and larger . Macrofauna are those animals 

retained on a 300 micrometer sieve and are typically collected with sediment in coring 

devices. A conflicting 500 micrometer standard has often been applied. Meiofauna is the 

smallest class defined by sieving. This category passes through a 300 micrometer sieve 

and is retained on a 63 micrometer . Even smaller classes are not normally studied in 

routine surveys and require either culturing or staining of microbes . 

2.2 .3 Megafauna 

Deep-sea megafauna are recognizable and give the deep fauna its distinctive 

nature to non specialists . The deep sea is characterized by an abundance of echinoderms, 

especially ophiuroids and holothuroids . Sea stars, urchins, and crinoids are also present, 

20 
but not in equally great abundance or diversity. The ophiuroids (serpent stars) are similar 

to those found in shallow water, but are more abundant as a general rule. The 

holothuroids, sea cucumbers, consist of species similar to those in shallow water and the 

order elasipoda with extremely modified morphology. Deep crustacea are usually not the 

true crabs of shallow water. Some deep fish have morphologies like their shallow water 

kin, but, many of relatively unrelated taxa share a common long tapering, "rat tail". 

Sessile colonial animals are rare, but elegant sea fans are encountered on hard substrate 

and dense populations of sponges sometimes encountered. These latter examples pose a 

challenge to the generality that the deep sea is dominated by deposit feeders. General 

management utility and limitations are presented in table 2.2 

Table 2.2 . Management Utility of Megafuana in Monitoring and Background Surveying 

Contracted to Limits of Utility. 

MANAGEMENT UTILITY LIMITS of UTILITY 

1 . Better Information Base (a) 1 . Ecological Generality Uncertain Since greatest 

More likely for some natural history contribution to diversity is in smaller size 

to be known. (b) Identification usually classes, knowledge of a few large animals 

easier and (c) More easily studied in may have little utility. 

situ and in lab. 

2. Better Suited for Organism-Level Impact 2 . Organism-Level Generality Uncertain As with I 

Assessment (a) Large tissue the above, ease of study does not means I 

volumes for analysis, and (b) easily results will be applicable to other species. 

assayed organs. 

3. Modest Sample Processing Costs 3. Trawl Sampling Difficult & Non Quantitative 

Compared to smaller fauna sampling, (a) Successful Deep Trawling is time 

most sorting and initial identification consuming, (b) requires special equipment 

is done at sea. and (c) experience ; (d) photo/video has 

relatively high taxonomic uncertain 

3. More Likely to Reveal Potential Conflicts 4. More Likely to Trigger Concerns Large crabs 

in Use (a) Large and fishes may be seen as potential 

animals more likely to have a fisheries even though the populations may 

resource value, and (b) large animals be unable to sustain fishing pressure . 

more likely to be publicly perceived 

as requiring protection. 

Ophiuroids 

Ophiuroids, commonly called serpent and brittle stars, are often the most 

abundant animal collected in trawls . There is no resource utilization and no general 

public interest in the class. Their abundance makes them an obvious choice as an 

indicator species. They tend to have wide depth ranges (Gage 1982) making the useful in 

surveys of large regions. Some species, notably Ophiomusium lymani, are thought to be 

cosmopolitan . If this observation holds up to molecular confirmation, it is another reason 

to focus upon these animals in monitoring studies. Deep ophiuroids seem to have the 

same range of natural histories as encountered in shallow water. They include deposit 

feeding, suspension feeding, scavenging, and predation. The author has even observed 

ophiuroids suddenly ensnare small fish . Given the range of natural histories and the high 

population numbers, the species of this class are probably very ecologically important. 

21 
Holothuroids 

Holothuroids, sea cucumbers, frequently vie with ophiuroids for the distinction of 

being the most abundant animals in deep trawl samples. There is no resource utilization 

of deep species, and no deep species is suitable for inclusion in the commercial trepang or 

beche-de-mer fishery (names applied to holothuroid fishery supplying the Asian market) . 

There is no special public interest in holothuroids, however, some deep species are 

colorful (purple or orange) and have such unusual morphologies that they can be 

considered exotic in the sense of attracting public interest in preservation . As in shallow 

water, infaunal and epifaunal detritus feeding are common although one or two 

suspension feeders exist. The most unusual groups are the benthopelagic taxa which 

swim in the BBL between feeding forays on bottom . At least two such families exist. 

Abundance and size make holothuroids good target species for monitoring and survey . It 

has been suggested that their extensive sediment feeding may control the habitat 

complexity required for the high diversity of smaller fauna. As such, they are one of few 

deep taxa for which a systems-level ecological importance has been proposed. 

Fishes 

Deep fishes are common in trawl samples, and the almost uniform black color and 

tapering `rat tail' bodies are characteristic of the deep sea. There are known resource 

conflicts. The organ roughy (Hoplostethus atlanticus), sable fish (Anoplopoma fimbra), 

and grenadiers (Coryphaenoides and related genera) support substantial fisheries ; 

although no such fisheries have been developed in the Gulf of Mexico. It is to be 

anticipated that as shallow fisheries collapse, there will be continued (possibly illconceived) interest in deep fisheries resources . Due to the great scientific and public 

interest in fish, they are ideal target species for monitoring and survey . In trawl surveys, 

the grenadiers are the most common group caught . This species/genus complex shares 

with most other deep fish the habit of feeding on bottom invertebrates and smaller fish . 

In baited camera and trap studies the predator/scavenger hagfish (Mixinidae) 

predominate. The predation pressure exerted by the fish population upon the populations 

of benthic prey species must be great, and predatory population regulation is to be 

suspected. 

Crustacea 

The distinctiveness of large deep crustacea lies mainly in a shift of composition 

rather than special morphologies. The true crabs decline with depth to be replaced by 

spider crabs, hermit crabs, and more lobster-like crabs such as the galatheidae (squat 

lobsters). There is actual and possible future resource conflict . The upper continental 

slope typically has populations of long-lived large crabs that are trapped or trawled. On 

the US Pacific coast this deep crab fishery targets spider crabs and is largely restricted to 

Oregon and more northern areas. In the Atlantic and Gulf of Mexico the true crab 

Chaceon quinquedens (long known as Geryon) is the target of a limited fishery and is 

22 
marketed as golden crab. A deep-sea shrimp fishery is also pursued in the Gulf of 

Mexico and south Atlantic states . 

Large crustacea are not as common as ophiuroids and holothuroids but are a fairly 

consistent part of a deep trawl sample . This lower abundance limits their utility in 

studies, but the possible resource issue and a well-established taxonomy offset this 

limitation to a large extent . The penaeid shrimp and hermit crabs are usually the most 

abundant large forms collected . Due to the great range in morphologies, it is to be 

suspected that crustacea play many ecological roles . Most are epifaunal, but a few 

extensively burrow the sediment, contributing to habitat complexity. 

Sponges 

Sponges are exceptions to the rule that deposit feeders predominate. Most times 

sponges are rare in trawl samples. However, there are obviously patches of bottom with 

high population densities. Such a "sponge bank" has been observed adjacent to the Orca 

Basin in the Gulf of Mexico (T. Bright, personal communication) and possibly 

encountered in the NGMCS study. There are no resource conflicts and the numbers are 

usually too few to make a good target species. However, their presence may indicate a 

special habitat. The Hexactinellidae, approximately 500 species of glass sponges, are 

abundant in shallow polar seas and the deep ocean. They may be an important 

structuring element in some deep-sea sediment (Bett and Rice 1992). Where boundary 

layer conditions provide increased suspended detritus to these microphagous filter 

feeders, high densities may be achieved (>1 M-2). In these relatively dense stands the 

sponges and associated fauna may comprise a sponge assemblage that is distinct from the 

surrounding benthos. Unlike shallow water where sponges encrust hard surfaces, the deep 

glass sponges are free standing on mud bottoms and provide a substrate for other 

organisms. Typical colonists are stalked and verrucamorph barnacles, hydroids, 

tunicates, braciopods, and crinoids. While seldom abundant, deep sponges are 

conspicuous in bottom photos/videos and comprise one of the major groups that can be 

studied by that method. 

Coelenterates 

Coelenterates are a consistent, but usually low abundance, component of deep 

samples. The numbers are usually too few to make a good target species. However, their 

presence may indicate a special habitat. Anthozoans are the dominant coelenterate in 

shallow and deep water. Unlike the shallow environment where there is alternation of 

generations between dispersive medusan morphologies and sessile forms, deep anthozoan 

are thought to lack the medusan phase. Species in the order Ceriantharia (burrowing 

anemones) are ubiquitous in the deep-sea and appear to be opportunist omnivores . These 

animals bury the posterior end of the body in the sediment and extend the anterior end 

and feeding tentacles out of the bottom. The more familiar shallow-water sea anemones 

(order Actinaria), are also found in the deep ocean either attached to hard substrate or 

resting on the sediment with a broad pedal disk. Order Pennatulacea (sea pens) also 

anchor in mud and sometimes form relatively dense aggregates in regions of high detritus 

influx . 

23 
Unlike the sediment dwelling coelenterates, Gorgonacea (sea fans), Alcyonacea 

(soft corals), Antipatharia (black corals), and Scleractinia (stony corals) all require some 

hard substrate for attachment . This may be massive exposed rock or bits of shell so small 

that they become indistinguishable as the animal grows . Due to the paucity of suspended 

food at depth, the presence of such animals is indicative of special environmental 

conditions. 

Corals are of considerable public interest . Therefore resource conflicts with deep 

oil and gas development are to be expected. Banks of the coral Lophelia pertusa in the 

North Sea (Wilson 1979) have raised public concerns. Similar banks have been located 

at approximately 800m on the Blake Plateau off Florida (R. Avent per. com.) . 

2.2 .4 Macrofauna 

Macrofauna are those animals smaller than megafuana that are retained on a sieve 

of either 500 [tm or 300 ~tm (the latter preferred). Traditionally, there has not be a sharp 

division into infauna and epifauna, since the sampling methods do not allow for certain 

classification. They are usually sieved or picked from a sediment sample. Assessment of 

ecological roles is speculative . In the deep sea most macrofauna are deposit feeders. 

They probably comprise the primary forage of many predatory megafauna. There is no 

current or planned resource usage and little public awareness of this group. However, 

macrofauna have become the primary focus of surveys and monitoring due to the very 

high data yield per sample. As a result, the macrofauna are the main component of 

measured benthic diversity. General management utility and limitations of utility are 

presented in table 2.3 

The pericarid crustacea, polychaete worms, and bivalve molluscs dominate deepsea macrofauna . There is a substantial, scattered literature on these faunal elements, but 

no comprehensive treatises. There are relatively few systematic experts. The prevalence 

of pericarids and protobranch molluscs contributes to the impression that the deep-sea 

fauna is ancient since both groups are considered primitive within their respective higher 

taxa. Low fecundity of some bivalves and the brooding mode of pericarids contributes to 

the impression that reproduction patterns are different in the deep sea. 

Polychaete Worms 

It is common for polychaete worms to be the most abundant and diverse 

component of the macrofauna . The families Ampharetidae, Paraonidae and Spionidae 

tend to predominate with specimens somewhat smaller than found in shallow water 

(Blake et a1 .1987) . The abundance and diversity of the group make them an excellent 

target taxon when total species inventory is impractical. The continental slope of the US 

Atlantic coast has the best studied polychaete fauna in the world . As a result, the 

taxonomy may be more tractable than is usual for this group. Worms are predominantly 

deposit feeders, but display a great range of foraging behaviors. Most are infauna, and 

their burrowing may be the primary determinant of bioturbation rates and depth. 

24 
Table 2.3 . Management Utility and Limitations of Utility of the Macrofauna Size 

Class in Background Surveying- and Monitoring. 

MANAGEMENT UTILITY LIMITS of UTILITY 

1 . Captures High Diversity Component (a) 1 . Less Liked to be Well Known (a) 

This is the faunal class from which deep limited information on species-level biology 

diversity concepts have been developed available and (b) great difficulty obtaining 

and (b) large number of species in sample correct identification due to new species and 

better suited for statistical analysis. few specialists. 

2 . Sampling Standardized and Effectiveness Well 2 . High Per Sample Processing Costs (a) postKnown (a) cruise sample picking and sorting under 

0.25 m2 frame mounted box cores have microscopes is time intensive and (b) correct 

become the standard for benthic studies, and consistent identification of specimens 

(b) biases due to devices known and depends upon a limited literature and few 

controllable, (c) sample processing well experts. 

standardized . 

3 . Results are Quantitative 3 . Results Difficult to Extend to Larger Fauna 

General public and other ocean users will 

relate more to larger fauna such as fishes. 

Pericardian Crustacean 

The Pericarida typically comprise about one third to one half of the species in 

macrofauna samples (Hessler and Wilson 1983). These small crustaceans include the 

very abundant orders Amphipoda and Isopoda along with the less abundant 

Tanaidaceans, Cumaceas, and Mysidacea. The peracarids are predominantly detritus 

feeders living on or just below the sediment-water interface. Reproductively they share 

the common feature of having a brood pouch and lacking dispersive larvae . The 

amphipods are most common on the continental slope and slope base, decreasing in 

importance in deep oligotrophic basins (Grassle and Maciolek 1992, Wilson and Hessler 

1987). Deep-sea species belong to families and genera also found in shallow water. This 

pattern has been interpreted to indicate multiple and ongoing colonization of the deep 

(Hessler and Wilson 1983) . The Isopods are very successful in the deep-sea. Isopod 

families span shallow and deep water; there is indication of radiation in the deep 

environment at the level of genus. 

Molluscs 

In shallow water it is common to find molluscs in the megafaunal size range. In 

deepwater they are generally much smaller. They are so common that they are the third 

most abundant taxon. The deep-sea molluscs are extremely diverse and are dominated by 

ancient taxa that are poorly represented in shallow water. Deposit feeders predominate. 

Allen (1983) and Knudsen (1979) have reviewed the general biology of deep bivalves . 

25 
Similar general reviews have not been produced for the deep gastropods, however, the 

geographically and taxa specific works of Bouchet and Waren (1986) provide some 

general information. 

Deep bivalve molluscs are dominated by the more primitive subclass 

Protobranchia. The shallow ocean is dominated by the subclass Lamellibranchia. In 

addition to small size, the deep species are notable for the lack of both color and shell 

ornamentation . Allen (1983) has posed the interesting speculation that deep protobranchs 

have diversified according to digestive strategies in a food-poor environment . Not all 

deep bivalves are deposit feeders. The Septibranchia are well represented predators 

(Allen and Morgan 1981). Unlike the deep bivalves that are dominated by a single taxon, 

deep-sea gastropods are in all three major groups of the class, Archaeogasatropoda, 

Mesogastropoda, and Neogastropoda; the names implying evolutionary age. Feeding 

types are not strictly associated with any one order, although deposit feeders tend to be 

Archaeogastropods and predators tend to be Neogastropoda . 

2.2 .5 Meiofauna 

Meiofauna is that faunal component smaller than 500-300 ~im and retained on a 

63 [tm sieve. As with macrofauna, they are usually sieved and picked from sediment, and 

division into infauna and epifauna is not practicle. However, various accepted methods of 

facilitating sample processing have been developed. An excellent comprehensive guide 

to study of the meiofauna has been compiled by Higgins and Thiel (1988) that includes 

sampling methods (Fleeger et a1 .1988) . That volume has been updated in a single author 

publication (Gieve 1993), that is less comprehensive but includes a better review of 

habitats . Neither reference gives detailed review of deep-sea fauna. The ecological role 

of the meiofauna is problematic; deposit feeders predominate. The group probably serves 

as forage for macrofauna . There is no current or planned resource use of the meiofauna . 

There is little public awareness. The use of meiofauna in applied ecology is greater in 

Europe than the US. Since meiofauna and macrofauna can be extracted from the same 

sample, there should be no additional field cost associated with including both groups . 

However, the taxonomy of the smaller group is so poorly known that lower taxonomic 

resolution and various faunal indices are usually used to keep the sample sorting work 

within reasonable bounds . Utility and limitations are summarized in table 2 .4 . 

Nematoda 

Our knowledge of deep-sea nematodes is very restricted by the poorly developed 

taxonomy of the group. They are probably the most abundant component of the 

meiofauna and may exceed the macrofauna in both number and diversity. As a practical 

matter in surveys that can not support a long taxonomic effort, the group must be treated 

as a whole and not sorted to species . 

Harpacticoid Copepods 

These small benthic copepods are less abundant than nematodes, but a better 

developed taxonomy makes them a useful tool in deep-sea studies. Three functional 

groups have been identified in deep sediments (Thistle 1983). One group has prominent 

26 
dorsal spines that anchor a mucus/sediment mix that probably serves as camouflage for 

these sediment-water interface dwellers . A second group consists of burrowers that use 

modifies appendages and setae in excavation . A third group has developed a vermiform 

body to assist in interstitial existence. Thistle found a taxonomic and morphological 

analysis to be very informative in comparing environments of different energy level. 

2.2 .6 MMS Management Needs 

When management focuses at the species level, data costs quickly become 

excessive. As a practical matter, it is necessary to select target species for detailed 

sensitivity studies and devise ways of gaining optimal information from collections 

sorted to less-than-species-level . Ideally, target species might be selected from the 

dominant organisms in each size category. Of special interest would be studies of the 

sensitivity of these species to turbidity, chemical discharge, and alteration of the habitat. 

Sensitivity studies should examine population-relevant parameters such as fecundity. In 

all the faunal groups the lack of taxonomic expertise is a critical factor . While it is not 

the obligation of MMS to revitalize the field of systematics, MMS should take steps to 

assure that deep-sea samples are studied in a timely manner by competent experts. 

Table 2 .4 . Utility and Limits of Utility of the Meiofauna. 

MANAGEMENT UTILITY LIMITS of UTILITY 

1 . Captures High Diversi , Component (a) 1 . Least Likely to be Well Known (a) 

This faunal class probably has a high limited information on species-level biology 

species richness and (b) large number of available and (b) most difficulty obtaining 

specimens in small samples are well suited correct identification due to new species and 

for statistical analysis . few specialists. 

2. Sampling Standardized and Effectiveness Well 2. Very High Per Sample Processin Costs (a) 

Known (a) post-cruise sample picking and sorting under 

subsamples from 0.25 mz frame mounted microscopes is time intensive and (b) correct 

box cores have become the standard for and consistent identification of specimens 

benthic studies, (b) biases due to devices depends upon a limited literature and few 

known and controllable, (c) sample experts. 

processin g well standardized . 

3. Results are Quantitative 3 . Results Difficult to Extend to Larger Fauna 

General public and other ocean users will 

relate more to larger fauna such as fishes . 

2.3 Zonation - The Depth Gradient As Multiple Habitats 

2 .3 .1 Summary Statement 

It is reasonably well established that benthic fauna changes progressively with 

depth with the pattern of change showing some regional specificity. The simplicity of 

this change with depth has lead to often confused debates about rates of change, where to 

draw imaginary lines, and appropriate nomenclatures (Table 2.5). Fortunately, this 

27 
debate has subsided and simple schemes adopted until more productive research can be 

carried out. In general, three faunal groups can be identified in most regions. There is a 

well-defined upper-slope (200-1000 m) group which drops out with depth, an abyssal 

plain fauna (greater than 3000m) which increases with depth, and a lower slope fauna 

(1000-3000 m) which overlaps the other two . Dividing these three into sub zones is 

highly arbitrary since the ranges of the component species overlap extensively. Gage and 

Tyler (1996) advocate a even simpler view that there are only two major faunal groups 

contributing to the apparent zonation. Avoiding the confusing terminology of 

predecessors, they recognize a bathyal zone corresponding to the continental slope and an 

abyssal zone . Compared to the actively researched and debated deep-sea topic of 

diversity, the study of faunal zonation is now a relatively inactive area. The identification 

and naming of zones, homogenous bands, summarized by Menzies et al . (1973), has 

largely ceased and been replaced by analysis of adaptations in taxonomically restricted 

groups. From the management perspective, this shift in research emphasis is unfortunate 

since knowledge of species change across the vast areas of the deep-sea is needed to 

determine what management strategies are needed in different areas. Clearly, it would be 

simpler for management if one faunal zone existed and extended over large areas of the 

continental slope and abyss. If, on the other hand, each region of the continental margin 

had a locally unique bathymetric pattern of species change, the management task will be 

greatly complicated. 

2 .3 .2 State of the Art 

The description of deep-sea faunal zonation is a less active area of ocean research 

now than ecological study of specific habitats, the biological study of specific organisms, 

and consideration of diversity-maintaining processes. There is little discussion of zone 

placement, names, and validity . Some resumption of species-level distribution studies 

should be anticipated by management as deep studies follow the lead of shallow 

biodiversity studies where description of distributions is being replaced by two lines of 

research (Butman and Carlton 1995). The first of these, characterized by the review of 

Palumbi (1995a) examines populations and larval transport using genetic markers 

(Palumbi 1995b) . The second is a critical reexamination using molecular genetics of the 

broad distribution of apparent cosmopolitan species (Knowlton 1993, Knowlton and 

Weight 1997). 

Dispersion studies and reexamination of cosmopolitan distributions are both of 

appreciable management impact since they challenge the current views available to 

management that : (1) the sea floor becomes faunally homogenous with depth due to an 

increase in species depth range, that (2) deep megafauna tends to be increasingly 

cosmopolitan with depth, and that (3) deep macrofauna shows an increasing degree of 

regional endemism with depth. The need to challenge these widely accepted ideas lies in 

the subjectivity of traditional taxonomy. Most deep-sea families and genera were 

established in the era of national ocean exploration (1880' s-1950). At that time, 

diagnosis of new species by taxonomists was strongly influenced by developing, often 

conflicting, concepts about ocean zoogeography. Physiological-based concepts of 

distribution held that the monotonous and stable deep environment below 1000 m should 

be dominated by cosmopolitan species. Evolution-based concepts, stressing isolation, 

held that each ocean basin should be populated by narrowly distributed endemic species. 

28 
The expert's decision to split or lump was, in large part, controlled by one or the other of 

these ideas . The unfortunate consequence is that present day deep-sea zoogeography 

may be greatly distorted by concept-biased taxonomy. Etter and Rex (1990) have begun 

reexamination of the North Atlantic deep molluscs using DNA techniques and found, so 

far, that the prevailing idea of widening vertical ranges with increasing depth is correct. 

For management purposes it may not be necessary to know that widespread 

morphological species are actually genetically differentiated species and sibling species 

complexes . Genetic screening of the deep-sea fauna would add great expense to any 

survey or monitoring effort . However, to ignore the possibility runs the risk of 

miscalculating the size of a potentially impacted population . One possible and cost 

effective means of solving this problem would be to continue emphasis upon 

morphological species study. New quality assurance and quality control portions of any 

study could include the requirement that a selection of dominant species tissue samples 

be cryogenically stored and archived in a repository that maintains such a collection . 

These samples could then be genetically screened during the course of subsequent 

museum-based research . 

2 .3 .3 History of Zonation Concepts 

A full discussion of the history of deep ocean zonation studies is of no particular 

management relevance and can be found elsewhere (Carney et a1 .1983, Gage and Tyler 

1996). However, it should be understood that zonation is a descriptive fact for which the 

actual causes remain unknown. Therefore, management decisions should not presuppose 

any particular mechanism. 

The fact that deep-sea species are restricted to vertical ranges of varying width 

was implicit but relatively speculative in early faunal studies. The first detailed 

discussion of this zonation and careful analysis of species data were given by LeDanois 

(1948), who favored temperature and sediment type as the causative factors. Until the 

advent of competition theory (reviewed by Paine 1977), zonation continued to be seen as 

being the result of physical factors . The great popularity of competition theory coincided 

with the rediscovery of high diversity in the deep-sea (Sanders et a1 .1965) and called into 

question the importance of community structure in that environment (Mills 1969). Could 

deep zones represent biotically controlled shifts in communities rather than physical 

control? 

It was reasoned that if integrated and biotically controlled communities existed in 

the deep sea, then the transition from one community to another might be sharp and 

unrelated to any obvious suite of physical parameters. Alternatively, physical control and 

an absence of interacting communities should produce gradual species change with any 

sharp changes coinciding with distinctive physical conditions . The relative importance of 

biotic or physical factors remains unresolved. However, a strong hint that biotic factors 

are important can be found in the work of Rex (1977) who found that the rate of species 

replacement with depth changes with the taxa and feeding type examined. To better 

interpret observed distribution patterns, Pineda (1993) and Pineda and Caswell (1998) 

have taken a neutral model approach to zones, finding that some patterns are simple 

artifacts of the upper and lower boundaries . 

29 
2 .3 .4 The Analysis and Criteria Problem 

The finding that ocean fauna changes with depth is one of the oldest and 

uncontested facts established in earliest ocean exploration. The issue becomes clouded, 

however, when attempts are made to describe this change and give explanations for it . 

Directly or indirectly, much of the problem lies in the choice of criteria used to recognize 

and describe compositional change . When drawing a map line showing a faunal change, 

there is an implicit assumption that a sharp fauna break actually exists . In many 

instances, however, the student of zonation may be employing criteria that impose a 

break upon the data that would not be found upon other analyses. A very brief historical 

review can illustrate this . 

Prior to the 1980's, deep-sea faunal zones were proposed and named without 

hesitation . Since the seafloor morphology and water column properties of the world 

ocean were far better known than the ocean biota, physical parameters were actually the 

primary criteria employed (Ekman 1953, Hedgepeth 1957) . Starting with LeDanois 

(1948) faunal distribution became the primary criteria for recognizing zones. However, 

employing physical criteria for dividing biological distributions was still used as in the 

zonation scheme proposed by Pequegnat (1983a) for the Gulf of Mexico. 

The history of zonation studies reflects an increasing sophistication of analyses . 

All such analyses are based upon the examination of a matrix of inter-site similarity 

coefficients . In the past, the relatively simple Percent Similarity Coefficient (Whittaker 

and Fairbanks 1958) and Bray-Curtis Coefficient received the greatest use. More 

recently, Normalized Expected Species Shared, NESS, (Grassle and Smith 1976) has 

gained popularity. NESS is conceptually appealing since it is based upon expected 

probabilities (Hurlbert 1971), but is computationally complex and only recently been 

incorporated into statistical computer programs. The actual analysis of the similarity 

matrix can either be clustering or multivariate ordination. The conceptual simplicity of 

the former has resulted in its more frequent usage. As with the choice of coefficient, 

there has been a progression in the techniques used. The Flexible Linkage clustering 

strategy gained popularity in the oceanographic community for what must now be 

considered an undesirable property. Flexible Linkage clustering is highly subjective; by 

changing a single parameter, the clusters can be "tuned" until a preconceived result is 

obtained . 

Analysis of similarity using ordination techniques is often viewed as the preferred 

method of zonation analysis since they eliminate the subjectivity and forcing inherent in 

cluster analysis (Carney et a1 .1983, Gage and Tyler 1996). However, these methods can 

be so conceptually complex that the final results are extremely abstract and of meaning 

only to the expert . Selection of a technique is difficult. Currently, Detrended 

Correspondence Analysis (Hill and Gauch 1980) is popular in benthic studies. 

Correspondence analysis is a technique intended to remove some distortions among 

relationships that principal component analysis and factor analysis impose . 

30 
Table 2 .5 . Depth Zone Names and Applicable Regions Proposed by Various Workers. 

Approximate Hedgepeth Carney et al . Pequegnat Gage & Tyler 

Starting Depth (1957) (1983) (1983a) (1996) 

Global NW Atlantic Gulf of Global 

Mexico 

< 200 m Littoral Shelf Province Shelf Shelf 

200 m Bathyal Shelf/Slope 

Transition 

250 m Transition Zone 

500 m Archibenthal Bathyal 

Upper Bathyal Zone 

Horizon A 

1000 m 

Lower Bath al Horizon B 

1500 rn Abyssal Upper Abyssal 

2000 m 

Upper Abyssal 

2500 m Mesoabyssal 

Meso Abyssal 

Horizon C 

3000 m 

Horizon D 

3500 m Lower Abyssal 

4000 m+ Abyssal na. Abyssal 

Lower Abyssal 

- 

6000 m+ Hadal Na. na. I 

2 .3 .5 MMS Information Needs Concerning Zonation 

MMS' primary need relative to deep-sea fauna zonation is to determine the degree 

to which species composition changes across the region of sea floor subject to 

development. There are two purposes for this information. 

Depth-Specific Management - If a region proves to be faunally homogenous then 

a uniform management strategy may by be employed. If a region contains 

distinct faunal zones then a suite of depth-targeted strategies may be needed. 

Confounding Factors - In subsequent effects studies, sample stratification must 

take into account any depth related natural fauna changes to prevent them 

from being confounded with possible impacts. 

The above information can be derived from a conscientious faunal survey 

employing high taxonomic resolution. It is very important that samples be spaced at 

31 
close regular intervals along depth transects to avoid zonation artifacts arising from 

spatial gaps in sampling. Emphasis should be placed upon generation of a high quality 

data base first and data summaries second. Useful descriptive analyses should employ 

the NESS similarity coefficient, cluster analysis, and ordination by a detrending method 

such as multidimensional scaling. Criteria need to be developed for the degree of faunal 

change needed before a change in management strategy is considered . 

2.4 Deep Diversity - The Most Confusing Management Concern 

The deep-sea benthos is very species rich, usually with a diversity maximum near 

the base of the continental slope (approx. 2000-3000 m), and this richness is quite hard to 

explain. The fact of this high and enigmatic diversity sets the deep sea aside from 

shallow water and poses something of a dilemma to management. How do you protect 

something that is so poorly understood? Unfortunately, as discussed below, our 

understanding of deep-sea diversity is really quite speculative and in a state of 

development. Thus, if the resource manager is going to make use of the developing 

concepts, they must understand the overall progress of concept development. 

Fortunately as a practical matter, a resource manager does not need to be a student of the 

subtleties of diversity theory . It is sufficient to know what the major processes are that 

maintain diversity and to adopt conservation measures which protect those processes. 

However, the burden on the manager increases when the underlying theory provides few 

practical guides and has not been rigorously developed through testing and criticism. 

Then, good management requires an understanding of the strengths and weaknesses of 

the developing theory so that preliminary management can lead to a fuller and more 

useful development of that theory . Unfortunately, deep-sea diversity theory as it now 

exists is of minimal immediate utility. 

The following sections are intended to do four things . First, definitions of 

diversity will be considered . Second, a brief explanation of diversity theory will be 

presented. Third, deep-sea diversity concepts will be presented in historical sequence. 

Fourth, management information needs about diversity will be developed. 

2 .4 .1 Definitions and Measures of Diversity 

Diversity can be a very troublesome concept to both researchers and managers. It 

is easy enough to define intuitively, but mathematical expression of it that permits the 

necessary analyses and rigorous testing tends to get much more complicated. Interpreting 

it relative to basic or applied ecology has proven to be exceedingly difficult. The 

difficulty of interpretation is compounded by the fact that many proponents of diversity's 

management utility have been uncritical of speculation of how diversity relates to overall 

ecosystem condition. While it is always hoped that some index of diversity might be a 

precise indicator of ecosystem health, this simply has never been established. 

Diversity is defined according to its intended use. Basic ecologists use definitions 

that derive from the resource utilization approach to ecology. Applied ecologists and 

managers usually want a simple descriptive definition . 

32 
Theoretical : Diversity is the variety of organisms in a given environment, habitat, 

or ecosystem. In a yet unknown way, it reflects the history of emigration and 

immigration along with the competitive utilization of resources by different 

species. Evolutionary splitting of species may also be a factor in isolated 

systems . The exact mathematical form of its expression is not of major 

import so long as it supports investigation of the underlying processes. 

Utilitarian: Diversity is the variety of organisms in a given environment, habitat, 

or ecosystem. It represents the state of the system and no inference needs be 

drawn about the underlying processes. The exact mathematical form of its 

expression must be uniform across many studies and support comparisons 

from place to place and time to time. 

The management need for simple indices has two origins . First, it facilitates 

comparison and analyses across varied studies. Second, it spares the manager the burden 

of having to deal with large and complex data sets . With the development over the past 

few years of computers that easily handle very large data sets, the need for standardized 

summary indices in ecology and many fields has greatly changed. If high-quality data 

are correctly stored, it is a simple and very fast task to calculate and compare every 

imaginable index . However, for comparison with past studies that may not have a good 

data archive, standard indices still have a place. 

A useful review of the dozen or more indices used in benthic ecology can be 

found in Washington (1984) and Margurran (1988) . Estimation of species diversity from 

deep-sea samples is usually hampered by sample sizes that are low compared to shallow 

water and very variable across a large region of study. Therefore, the very close 

relationship between sample size and species richness has received considerable attention 

in deep studies and is of considerable management interest . A very well written text on 

rarefaction (estimating species richness in a reduced sample size) and abundifaction can 

be found in Hayek and Buzas (1997) Surveying Natural Populations . Sanders (1968) 

initially devised rarefaction as a graphical means of comparing species richness between 

unequal samples. His method is simple and effective, but mathematically flawed. 

Hurlbert (1971) developed Sander's method in the mathematically correct form based 

upon the hypergeometric distribution . The most important thing to remember about 

diversity indices is that none of them convey any special information about the 

underlying processes behind diversity. Thus, there is no universal "best" index. The 

choice of index is dictated by the questions being asked. There are basically three 

approaches to diversity. 

The Inventory and Simple Species Richness 

Due to the utility and popularity of diversity indices, it is often overlooked that an 

inventory of species is not just raw data, it is an excellent expression of diversity. This is 

the simplest and most easily understood of all approaches and directly links the abstract 

notion of diversity with the actual species . When a mathematical expression is needed, 

the number of species in an inventory is the simplest diversity statistic and is typically 

called Species Richness. There are two criticisms of Species Richness that greatly limit 

its management utility. First, it does not consider abundance, leaving management with 

no tools for allocating study effort . Second, it is exceedingly sensitive to sample size . 

33 
Species richness is frequently used in theoretical work where sampling is not a problem. 

There are ad hoc methods of judging whether most of the species have been taken in a 

survey . These are based upon the rate at which new species are collected as sampling 

progresses . At some point, fewer and fewer new things are found, and sampling is 

judged to be adequate 

Simple Probability-Based Diversity Index 

When a species inventory contains data on proportional abundance, probability 

theory affords parsimonious ways of summarizing population patterns. Ideally, diversity 

indices allow for comparison of diversity among samples without having to standardize 

the sample size . The first index based on proportions was Simpson's A, but it is seldom 

used. Shannon's H' based on information theory (Shannon 1948) is widely used in 

applied ecology and is contractually required by MMS. Normalized Expected Species 

Shared NESS (Smith and Grassle 1977) has been extensively used, but is seldom 

included in statistical packages. 

Simpson's A is the oldest probability-based diversity index. Simpson reasoned 

that a simple measure of the diversity of a particular habitat would be the probability of 

an observer encountering the same species twice in a row. The great appeal of this 

approach is that it may have some ecological reality to it . Probability must play a role in 

predator-prey encounters, breeding encounters, competition encounters, etc. The 

perceived problems of probability-based indices are all associated with the nature of 

proportions. High proportions produce high probabilities, and low proportion species are 

much less important. Simpson's A is based upon the square of proportion, making the 

relative importance of rare versus common things all the worse. 

The most useful modification of the probability approach is the development of 

Normalized Expected Species (Smith and Grassle 1977). This index directly addresses 

the problem of sample size by calculating the expected number of species in a 

hypothetical sample of a specified size . This size, however, must be equal or lower than 

the actual sample. In other words, it can not be used to estimate species number in a 

hypothetical sample larger than any sample actually taken. Expected Species is an 

extension of Sander's rarefaction method. It is unfortunate that Expected Species is not 

widely used since it has very nice properties. It is a simple extension of species richness . 

It employs relative abundance in its estimation, and a wide range of abundance makes 

equal contribution to the index. Furthermore, it has the practical benefit of defining 

acceptable sample size . If 500 individuals is the level to be used, sampling can be 

optimized to produce that 500, and samples judged as adequate or not on the basis of 

having at least 500 specimens. 

Information Theory Diversity Index 

Information theory deals with the successful transmission of information through 

media that are inherently noisy. It can be considered a branch of probability theory. 

Margalef (1958), receives credit for the use of common information, H', as a diversity 

index. He argued that in an evolutionary or succession sense communities were 

analogous to information channels. Pielou quickly discounted this analogy, and it is 

34 
rarely mentioned now. However, even if you strip common information of its proposed 

ecological relevance, it remains a mathematically useful formula. Whereas probability is 

based upon multiplying proportions, information is based upon logs of proportions. H' is 

a poor choice of indices for deep benthic studies. The index is best used when the 

dominant species exceed 50% of a sample. In the typical deep-sea study the most 

abundant animals are less than 20%. These mid-to-low percentages completely dominate 

the analysis, and the many rare species make no contribution . 

Multispecies Competition Models 

The following material is intended to establish the intellectual framework within 

which deep-sea diversity theory has been developed. The problem may be quite simply 

summarized. Simple and credible mathematics models indicate that when two or more 

species compete for a common resource, one will eventually displace the other(s) by 

competition. Why then are environments so full of many different species? The answers 

range from simple to complex and from plausible to dubious. The simplest is that there 

really are many resources and little or no competition is taking place. A bit more 

complicated is claim that there are numerous resources but not enough to prevent 

competition, and that various other processes intervene to prevent competitive exclusion. 

Intervention models can get quite complex and ultimately take the form of a mutualism 

argument . 

The basic mathematics model of competing species was developed by Gause 

(1934) as an extension of the Lotka-Volterra population growth model . Levins (1968) 

extended them to multi-species form . Prior to May's (1973) exploration of stability and 

complexity in model ecosystems, a common explanation for high levels of species 

diversity was that competitive interaction between two species was in some way 

mediated by addition of a third, fourth, and so on. Ultimately, the more complex the 

community, it was argued, the more stable . May showed quite convincingly that neither 

stability nor complexity produces the other. Furthermore, competitive exclusion is to be 

expected except for special community matrices . If you are faced with a species rich 

community and you do not want to invoke increasingly complex intervention models, 

your principal explanation must be that there really are many resources available and 

competition is minimal. 

2 .4 .2 Ideas About Deep-Sea Diversity 

Historical Development, Stability-Time to Cropper Hypotheses 

While proponents of various explanations for high biological diversity can argue 

the merits of their ideas, proof of any particular hypothesis is lacking and supportive 

evidence equivocal. To a large degree, the progression of ideas has not been driven by 

tests, falsification, and alternative hypotheses . Rather, growing information about the 

environment's physical heterogeneity and temporal pulsing (Smith, 1994) has been 

factored into diversity explanations which initially struggled with explaining high 

diversity in what was then viewed as a monotonous environment. Of course, this lack of 

a history marked by rigorous debate, extensive field observation, and hypothesis testing is 

not a just criticism of deep-sea diversity research . There have been too few people, too 

35 
few facilities, and too few opportunities for the history to be otherwise. However, this 

history poses a dilemma in seeking a scientific basis for deep-sea diversity conservation ; 

none of the ideas can be ruled out and none may be right. 

An understanding of the extent to which deep-sea diversity concepts are untried is 

best developed through a brief historical review. More detailed reviews of the content 

and development of ideas can be found in Grassle (1989), Rex (1983), Gage and Tyler 

(1996) and, Rex et al .(1997). Unlike the fall into obscurity of the Challenger discovery 

of high deep diversity, the findings of Sanders et al .(1965) were immediately recognized 

to be a paradox of the plankton question (Hutchinson 1961), asking how so many species 

can arise and coexist in such a seemingly monotonous, homogenous and undivided 

environment? In the context of competitive exclusion thinking at that time, the answer 

put forward was quite bold, the Stability-Time hypothesis (Slobodkin and Sanders 1969). 

This hypothesis, or explanation, essentially said that competition in an environment that 

is stable over very long periods of time leads to coexistence through a type of resource 

partitioning termed accommodation, not exclusion as might be predicted for such a 

system . This explanation for high diversity fully accepted and built upon the monotony 

and homogeneity of the deep sea. 

The Stability-Time hypothesis gained some acceptance in shallow marine studies 

of apparently stable systems but was largely ignored by terrestrial workers who were 

rapidly abandoning similar temporal-stability explanations for tropical diversities in favor 

of herbivore/predator effects (Janzen 1970) and long-term habitat change (Prance 1982). 

Biological control in the deep-sea was first introduced as the Cropper Hypothesis 

(Dayton and Hessler 1972) borrowing directly from intertidal ecology. Grassle and 

Sanders (1973) corrected an omission in the Cropper Hypothesis, but rejected it as being 

inconsistent with the few known life histories of deep species, interpreted by those 

authors as K rather than r selected. No testing of the Cropper Hypothesis per se was 

conducted. Except for an attack upon epistemological limitation of the Stability-Time 

hypotheses that concluded that deep-sea diversity is just another diversity-area 

relationship (Able and Waiters 1979), all subsequent explanations for the diversity have 

explicitly invoked environmental heterogeneity as a diversity maintaining factor. Thistle 

(1983) used diversity predictions based on the Stability-Time hypothesis to compare a 

less physically stable abyssal area in the northwest Atlantic with a more stable bathyal 

site in the eastern Pacific and found no support for the hypothesis . 

The adoption of hypotheses that stress heterogeneity of the deep-sea environment 

is due in large part to two factors. First, seminal ideas about population dynamics and 

evolution in patchy environments such as Levins (1968) were influencing deep-sea 

workers. Second, increased deep reconnaissance and monitoring of the deep-sea floor 

showed that it was reasonable to think of that environment as patchy. In reviewing these 

sources of variation over small (1 m2) to large areas (100 - 1,000's km2), Smith (1994) 

has stressed the pulsed nature of bioturbation, benthic storms (Thistle et al . 1985) and 

detrital influx (Lampitt 1985). Since habitat change occurs in pulses, processes 

ultimately controlling diversity might also be sporadic, intense, and localized. According 

to models of species in patchy space, high diversity may be maintained if the outcome of 

competition differs among patches. Such high diversity may exist within a patch or 

summed across many lower diversity patches, depending upon exactly how dispersion 

36 
and local-regional interactions are modeled (McLaughlin and Roughgarden 1994) . 

Efforts to explain deep-sea diversity in terms of habitat patchiness have focused on using 

faunal samples to determine the scale of patches and sampled or experimentally 

simulated bottom structure to identify the agents of such heterogeneity. 

The infusion of patch-related thinking into the deep-sea took place largely in the 

1970's during innovative studies in the laboratory of Robert Hesseler of Scripps 

Institution of Oceanography. The focus of these studies was the role in diversity 

maintenance of the biogenic structures created by the interaction of flow and biological 

activity. Central to the development of these ideas was sampling at controlled scales and 

in-situ experimentation. Important faunal scales were examined by clustering samples at 

different scales, partitioning box cores into sub samples, and employing remote devices 

to collect multiple samples from known positions over an area of approximately 500 m2. 

The studies were summarized and reconsidered by Jumars and Gallagher (1979) and 

Jumars and Ekman (1983). These ideas, which can be called the Grain-Matching 

hypothesis, did much to refine ideas about spatial scale and cause testing of patchyenvironment hypotheses. Four points remain especially important. First, faunal 

distribution patterns can be found on many scales, but the scale on which intra-species 

interactions occur in a succession mode are probably quite small, approximately the same 

size as the organisms themselves . Second, biogenic structure should be more persistent 

in the deep sea and is likely to be a very important agent of habitat heterogeneity . Third, 

the statistical power associated with analyses of faunal dispersion is very low, 

introducing considerable uncertainty into the analysis of surveys . Forth, significant 

progress in understanding how competition regulates diversity will require an 

understanding of what resources are being utilized by the fauna. 

Patchy Environment Grain Matching 

The points drawn from controlled sampling by Jumars and his associates had a 

strong influence upon in-situ experimental studies of the role of heterogeneity, especially 

the studies on the interaction of macrofaunal structure upon meiofauna diversity and the 

effect of simulated megafaunal mounds upon macrofauna. Eckman and Thistle (1991) 

demonstrated that water flow around the ball-like mud tube of the polychaete Tharyx 

luticastellus influenced some meiofaunal distributions. This effect was attributed to 

alteration of the sediment-water interface in the area around the mud ball by 

hydrodynamic flow. Smith et al .(1986) simulated the sediment mounds of large infaunal 

deposit feeders and found rapid colonization of this biogenic structure. The experiment 

was repeated with refinements (Kukert and Smith 1992) and the results produced 

evidence of immediate effects, longer-term succession effects, and an eventual return to 

near background conditions. 

Since the artificial mound studies were so well designed and executed it is 

important to look at the results closely. Did the artificial mound constitute a patch that 

might contribute to the overall high diversity of the bottom? The dominant species in the 

background fauna, Levinsenia oculata was also dominant in all samples of the 

experiment. Few of the rarer species with enough specimens to be included in analysis 

showed any effects through time . The mound showed no evidence of being a haven for 

rarer forms in the sense that none of the rarer forms were elevated to dominance during 

37 
the sampling period . The results of Schaff and Levin (1994) are particularly noteworthy 

in this regard . At a depth of approximately 800 m in the Atlantic off North Carolina, 

they targeted submersible sampling at conspicuous biogenic structures . They found no 

significant difference in the fauna between the background and the biogenic structure. In 

conclusion, these manipulations have shown that populations respond to alterations . 

However, it is not yet clear that such responses reflect the processes that maintain high 

diversity. Far more comparative study needs to be done. 

Patchy Environment Contemporaneous Disequilibrium 

An alternate hypothesis, termed the Contemporaneous Disequilibrium hypothesis 

has been developed by Grassle and his associates based upon the slowly accumulating 

information on the natural history of deep-sea fauna (Grassle and Sanders 1973), 

observation of detrital input periodicity, and extensive surveying on the continental slope 

(Grassle and Maciolek 1992). The central idea is that not all biogenic structure is 

important . Some structure and bottom hydrodynamics interact to create patchy 

deposition of labile organic detritus. Changing biological structure and extended postdepositional diagenesis in these special patches then provides the resource diversity to 

support a diverse fauna in a mosaic of succession stages. As a food-driven heterogeneity, 

these different patches can support higher-than-background source populations . Adult 

larval exported from these source patches maintain diversity over the much larger food 

poor areas. The Contemporaneous Disequilibrium idea has also gained some support 

from experimental studies. Colonization of defaunated sediment boxes showed very slow 

recruitment rates (Grassle and Morse-Porteus 1987), while colonization of food enriched 

sediment showed treatment faunal densities an order of magnitude greater than controls 

and ambient in just 23 days (Snelgrove et al . 1992). 

2.4 .3 Larger Scale Views of Diversity 

While the dynamics of inter-species competition in small-scale patches on the sea 

floor are important in local diversity maintenance, other processes and historical events 

on regional scales control the available species pool (Ricklefs 1987). Rex et al .(1997) in 

press) provide an extensive review of large-scale diversity patterns in the deep-sea. The 

first and most fully considered of deep-sea diversity patterns was that western Atlantic 

benthic samples showed a distinct diversity maxima between 2000 m and 3000 m, which 

has been termed a parabolic pattern (Rex 1983) . Application of the word parabolic 

invites explanations in which there are two interacting processes. 

Huston's (1979, 1994) dynamic equilibrium model seemed applicable to the deepsea diversity maximum and had the great benefit of leading to testable hypotheses about 

competition and predation gradients with depth (Rex 1983) . According to this model, 

diversity is suppressed by competitive exclusion as an area reaches equilibrium, while 

diversity is promoted or permitted by predator and abiotic disturbance. The difficulty 

with this and other models employing competition is poor linkage to known gradients in 

the deep-sea. Pressure has the most simple and ever increasing gradient . It does impose 

physiological limitations of the fauna, but it would seem to have no link to competition. 

It is now well established that the influx of organic detritus is a negative exponential 

function of depth (Rowe and Pariente 1992), and population size should be linked to food 

38 
input. It is less clear, however, if increasing food should be limiting diversity via 

competitive exclusion by larger populations, or promoting diversity through an overall 

increase of resources. Indeed, the diversity maxima may simply reflect the depth mode 

of an environmental factor such as sediment texture as suggested by Gray (1974) or 

sediment diversity as found by Etter and Grassle (1992) . 

In the context of competing processes that vary in opposite directions with depth 

it may be worthwhile to modify the argument of Able and Waiters (1979) that high deepsea diversity is simply another manifestation of the ubiquitous species-area curve. Taken 

alone, the hypsometry (distribution of depth) of the ocean leads to the prediction that 

diversity will be greatest at abyssal plain depths below 4000 m, not shallower as it has 

been found to be . However, if the exponential decrease in food with depth is combined 

with hypsometry, then a maximum on the lower continental slope may be expected. If 

species are to some degree bathymetrically restricted by low detritus influx, then 

historical increases in influx may have spread species across the vast area of the abyssal 

plain, and decreases caused restriction to the slope. 

A less well-established diversity gradient in the deep sea is that of latitude in 

which diversity is higher at tropical latitudes than boreal and Arctic (Rex et al . 1993). 

Since this finding has been based on scattered and dissimilar studies, it has been attacked 

as an artifact of regional glaciation effects (Gray 1994), and as conflicting with other 

results (Brandt, 1995). These criticisms should not be taken too seriously as yet. Indeed, 

glaciation may be one of the important causal mechanisms behind latitudinal gradients 

even in deep water. There was a distinct change in benthic foraminifera dominance in the 

north Atlantic at the Pleistocene-Holocene transition (Schnitker 1979). It appears that it 

took place progressively over the continental slope beginning about 15,000 years ago at 

1000 m and only reaching completion at 5,000 m 5,000 years ago . Similarly, criticism 

based on conflicts with regional-scale patterns is misguided. Even over distances of 

several hundreds of kilometers, intra-region variation in diversity may be expected to 

mask latitudinal trends . A novel example of this is approach of Voight and Walker 

(1995) comparing epibionts on the gastropod Gaza sp. from the continental slope of the 

northern Gulf of Mexico with Caribbean specimens; higher diversity in north was 

attributed to differing sediment regimes rather than a refutation of latitudinal patterns . 

2.4 .4 MMS Information Needs 

Identifying MMS' need is simple ; obtaining it is the hard part. Management 

needs to know exactly what the diversity maintaining processes are and then regulate 

industry activities so as to minimize disruptions. Current deep-sea ecology does not 

identify those processes conclusively . Of the two views, a homogenous environment 

with complex competition or a heterogeneous environment with normal competition, the 

second is more tractable. If the deep benthos is a habitat rich system on the very small 

scale, then the physical and biological processes causing this variety must be known and 

protected . Presently, these appear to be creation of biogenic structure, flow interactions 

at the sediment water interface, and redistribution of detritus . 

There are practical needs concerning surveying fauna and producing diversity 

analyses . The need for a diversity index as a descriptive summary statistic in species 

inventories has been greatly reduced due the ease of use of interactive data base analysis. 

39 
However, retention of the index facilitates comparison to older studies and assures the 

data continuity that MMS requires in its contracted surveys and monitoring. 

2 .5 Ecosystem Processes 

2 .5 .1 Biomass and Trophic Structure 

Environmental managers have often faced the criticism that they did not follow 

the lead of academic ecologists in switching from species inventories to process-oriented 

studies. Such criticism however, is seldom accompanied by convincing arguments that 

knowledge of particular processes is management relevant. Upon review of current 

concepts of deep-sea ecology, it does appear that the influx of organic detritus and the 

biogenic structuring of the benthos are processes of considerable management relevance . 

This apparent relevance stems from the ideas that both processes are far more important 

in the deep sea than on the continental shelf. The influence of detritus influx is most 

readily seen in biomass or population density data. The vertical pattern of biomass in the 

ocean is the simplest bathymetric trend, the most easily measured, and the readily 

interpretable of all biological depth gradients. Excluding the relatively rare 

chemosynthetic systems, productivity is limited to the upper photic zone. The consumer 

community of the upper mixed ocean is relatively efficient at retaining much (90 to 95%) 

of this productivity . Thus deeper bottoms are dependent upon a meager detritus influx . 

The longer this detritus is in transient to the bottom, the more degraded it becomes with 

the results that biomass decreases progressively with depth. Biogenic structuring is much 

less understood, but bioturbation studies are the starting point for future research . 

There are four primary management consequences of the pattern of organic 

detritus influx . 

" Biomass harvesting (i .e . fishing) is unlikely to be a serious conflicting use of the 

deep-sea floor. 

" Dramatic biomass differences between the slope-shelf break at 200 m and the 

slope bottom at 3000 m suggest that these environments are different and 

may require depth specific management strategies . 

" In areas of low biomass, food may be so rare and limiting that disruption of 

natural patterns of detritus input may be the primary agent of environmental 

impact. 

" The response of bottom populations to natural variation in detritus influx may be 

a major source of confounding variation when seeking environmental 

impacts . 

Identifying the Flux 

Prior to the 1970's ideas about deep-sea biomass were greatly influenced by 

Danish and Russian sampling in the hadal trenches adjacent to continents. Since these 6 -

11 km deep special environments at the continental margin had relatively high levels of 

standing stock biomass (Braun 1957, Belyaev 1966), depth per se was considered less 

important than distance from land in regulating biomass. The weight of evidence now 

indicates that for most regions of the ocean, depth is the more important factor. 

Examination of biomass versus depth for benthic fauna and for deep-ocean plankton 

40 
(Vinogradov 1961) shows an exponential decline in biomass with depth. Place to place 

variation in this curve has been attributed to surface productivity (Rowe 1974), width of 

the continental shelf (Rowe and Haedrich 1979), and latitude (Belyaev 1966). However, 

the actual controls are poorly known. 

The primary source of food for the benthos is organic material sinking down from 

the photic zone (Fowler and Kanuer 1986). This material which leaks into the deep-sea 

from the euphotic zone is approximately 10% of the productivity (Walsh 1992). Large 

food falls are apparently rare in the larger scheme of things (Stockton and Delaca 1982), 

but may be locally important (Smith 1994). There is clearly a scavenging component of 

the fauna adapted to exploit both recent carcass falls (Isaacs and Schwartzlose 1975) and 

the longer-term chemical environment they produce (Smith, et . al 1989). Even the 

relatively rare sinking of wood into deep water is exploited by a specialized community 

(Turner 1973, Maddocks and Steineck 1987) . It is thought that adaptation to very low 

food levels is the main evolutionary theme in the deep-sea fauna (Jumars et al . 1990). 

A full determination of which component of the detritus flux carries the most food 

to the benthos has not actually been made. Fine particles (< 10 gym) are unlikely to carry 

much nutritional value since they are in transit too long. Much larger particles (> 1 cm) 

sink much faster and carry more material, but seem to be relatively uncommon. Thus, 

mid-range material (10-500 gym) is the most likely candidate (Fowler and Knauer 1986). 

One of the most seminal observations in deep-sea ecology was the episodic and rapid 

sinking of phytoplankton blooms to abyssal depths (Billett et a1 .1983, Lampitt 1985) . All 

at once this suggested many things . First, it laid to rest any residual ideas that the deep 

sea is a stable environment. Second, it showed that while the deep-sea may be food poor 

much of the time, there are period of relative plenty . Lastly, the observation that BBL 

conditions redistributed the detritus pulse into a complex patchwork on the bottom 

suggested a mechanism for environmental heterogeneity . 

A six year time series of detritus flux measurements at 3200 m in the north 

,Atlantic (Deuser, 1986) revealed a range of inputs varying by a factor of 2.3x between 

minimum and maximum. Smith and Baldwin (1984) demonstrated that benthic 

metabolic consumption varied in response to such influx variation. Tyler (1988) and 

Tyler et al .(1994) suggest that breeding in some species may be keyed to high levels of 

influx . Thus, it may be assumed that population levels will vary in response to year to 

year differences. 

Missing Pieces of the Puzzle 

Four major discrepancies have been noted in our understanding of how detrital 

flux fuels the deep benthos (Carney 1989) . These are : 

" Biogeochemisty indicates that detritus becomes highly refractive in transit to 

bottom, but its rapid consumption on the bottom indicates that it must be 

biologically labile . 

" Biological estimates of detritus utilization indicate rapid consumption in 10 to a 

few 10's of days. Geochemical estimates suggest slower utilization of 15 to 

150 days! 

" Calculated biological demand may exceed apparent supply (Smith 1987). 

41 
" The isotopic content of deep fauna is not always freshly input carbon (Pearcy and 

Stuiver 1983). 

There are still pieces of the puzzle missing, but these may simply reflect the 

current crude state of measurement. Benthic ecologists determining the energy needs of 

the benthos find that most, if not all of the influx must be labile material to support the 

measured need. By contrast, studies of the sinking material indicate that the influx 

should be highly refractory due to bacterial attack during sinking. While it is tempting to 

invoke bacterial infallibility (bacteria can eat anything) and the resulting biomass as food 

for the benthos, this is trophically unlikely . To support bacterial metabolic needs, as little 

as 15% of the influx might be converted to labile bacterial biomass. Thus, there would be 

far too little material to support the metazoan benthos. The most likely explanation is 

that the benthos is feeding off a labile detritus which is not the same fraction being 

collected in traps and studied by the organic geochemists. 

The Suess and Rowe Relationships 

Benthic ecologists have a good general understanding of the gross patterns of 

detritus influx and the biomass that it supports. This understanding is based upon 

compilations which have been confirmed in many studies. Suess (1980) compiled data 

comparing euphotic zone primary productivity with apparent carbon flux at progressive 

ocean depths and used regression to generated equation 1 . 

1 ~ Cflux - Cprod / ( 0.0238*Z + 0.212 ). 

Where C flux is the flux of organic carbon at any given depth and Cprod is the 

primary production . Z is depth in meters such that Z must be greater than 50 m. Suess 

chose this formulation by analogy with a chemical reaction so that a process rate could be 

calculated. Inspection of the equation shows that only about 10% of the euphotic zone 

productivity makes it below 1000 m. Thus, based on Suess, little productivity is expected 

from mid-slope and deeper. 

Macrofauna biomass in the world ocean was compiled by Rowe (1983) based 

upon 709 quantitative samples reported in 36 publications . This remains the definitive 

compilation, and in spite of many possible biases associated with different sampling and 

processing methods, it affords the deep-sea manager a simple picture of how typical biota 

changes with depth. Describing biomass decrease with depth as an exponential decrease 

is more than an algebraic convenience . It reflects a biologically realistic process. The 

basic form of the relationship is given in equation 2 after Rowe (1974, 1983). 

2 M = Ae bz where M = biomass in g/m2 wet weight 

e = the base of the natural log 

A = Biomass at 0 depth 

z =Depth in meters 

b =exponent 

Determination of A and b from field data is usually based upon regression of the 

42 
log transformation, equation 3 . LogA is simply the intercept and b the slope of the line . 

3 LogM = LogA - bz 

Negative exponentials are found whenever some process decreases an initial 

amount of material by a fixed fraction over and over again during a fixed unit of time. 

For example, let primary productivity inject 1 kilogram of sinking biomass into the upper 

ocean. It is immediately colonized by bacteria and attacked by consumers as it sinks. In 

one hour, 50% may be consumed, and the next hour another 50%, and so on. If this 

scenario is plotted against time, a negative exponential is seen. When sinking rate is 

constant, time and depth are readily interchangeable. 

Treating b, the rate of consumption of sinking biomass, as a constant over all 

depths is a biologically unrealistic simplification, but it is justifiable at this time due to a 

lack of more detailed information. It probably decreases in the water column with depth. 

Low temperatures may inhibit bacterial activity, and the declining zooplankton will be 

less likely to consume the material that passes by. If management of the deep-sea ever 

requires a detailed understanding of natural biomass fluctuations, then the processes of 

degradation will have to be more fully explored . 

Using logarithms to the base 10, Rowe found the following relationship: equation 

4. When this equation is considered two important patterns are found. First, biomass can 

drop by half over as little as 500 m or as much as 2000 m. Second, most biomass decline 

can be expected on the upper slope above 2000 m. 

4 Log1oM = 1 .25 - 0.00039z 

The primary management value of the Suess detritus relationship and the Rowe 

biomass relationship is that they provide standards for comparison . If a particular 

region's measured influx fits the Seuss relationship well, then it is not an unusual deep 

environment. Similarly, if the biomass agrees with the Rowe relationship, it is a typical 

system. Departures above or below either relationship should be examined very carefully 

to determine exactly why the system is unique. It might be exceptionally productive, or 

especially stressed by natural conditions. 

Management Consequences of Biomass Decrease: Deep Productivity and Fisheries 

This report does not focus upon the issue of deep-sea fisheries. In theory such 

fisheries are possible if very carefully managed. However, the dramatic failure of 

presumably well managed fisheries targeting well known shallow-water species should 

cast serious doubts on any deep ocean plans. As traditional nearshore fisheries targeting 

top predators have collapsed, fishermen have switched to different target species. This 

shift has resulted in the exploitation of lower trophic level fishes in the upper ocean and 

deep demersal populations. The pressure to expand deep fisheries will persist, and ocean 

managers must anticipate resource conflicts. These mineral-versus-fish conflicts will be 

different from those which have taken place in shallow water because deep fisheries are 

new rather than traditional . In effect, the fisheries proponents know as little about the 

environment as the mineral developer. An excellent and comprehensive account of deep 

fisheries has been written by Merrett and Haedrich (1997) . 

43 
There is a small deep-sea fishery for crabs, shrimp, and rattail fish in the US. 

However, the best documented fisheries are in the Northeast Atlantic and the Indian 

Ocean. The orange roughy fishery is the best studied. Orange roughy (Hoplostethus 

atlanticus ) is a slope-dwelling species found over a variable depth range between 500 

and 2000 m. It grows to more than 50 cm in length and has desirable market properties. 

Prior to the discovery of spawning schools over topographic highs between Australia and 

New Zealand (Robertson 1991) it was considered a relatively rare species. Fishing with 

trawls began in the 1980's, peaked in about 1988, and declined subsequently . Orange 

roughy does occur in the northern Gulf of Mexico, but is not fished as yet. 

Merrett and Haedrich make three strong cases against large scale deep ocean 

fisheries, both which relate to the biomass decline and trophic structure of the deep sea. 

First, fish populations show the Rowe biomass decline. Unusually high biomass species 

are rare and of considerable age. Second, in shallow water commercial fish species are 

seldom the terminal predator. Therefore, fishery is just the addition of one more predator 

to species adapted to predation. This is not true in the deep. In that environment fish are 

the top predator and the populations are not adapted to being prey. Thus, populations 

may be unable to sustain exploitation. The third argument, related to the first, concerns 

age structure. Due to the low food input to the deep, many large animal species have 

spent many years growing to reproductive size. Therefore, harvesting targets a biomass 

that turns over very slowly. It may require decades for populations to recover from even 

minimal fishing pressure. 

2 .5 .2 Bioturbation Tracks and Trails 

Biogenic structuring of sediments has been proposed as a very important diversity 

maintaining process, but not well studied in that context. Conceptually, a simple 

experimental means of estimating the kinds and rates of such modification could be 

devised. However, such development has not taken place as yet. The specific study of 

animal-sediment interaction has been incorporated in some deep-sea programs as an 

ancillary activity in faunal surveying. In this section, the topic is briefly reviewed, 

inherent limitations identified,.and future uses suggested. Two main types of animalsediment interaction studies have been attempted in deep-sea applied ecology programs : 

the study of lebenspurren and the study of bioturbation . The first is related to the 

paleontology field of ichnography and studies tracks, trails, and other marks made by 

animals on the seafloor . The second derives from the study of chemical tracers in marine 

sediments and considers the effects of biological stirring upon gradients. 

Tracks and Trails 

Oceanographers have treated lebenspurren in three ways. First, it has been 

simply a description of an obvious and pervasive small scale topography (Ewin and 

Davis 1967, Heezen and Hollister 1971). Second, the various marks have been treated as 

surrogates for observations of animals. The hope was that surveys of tracks and trails 

might provide estimates of population density. Third, the actual trace morphology has 

been examined in an effort to learn something about foraging behavior of deep-sea 

animals. This behavioral aspect grew out of the paleontology work of Adolf Seilacher 

(1967) who interpreted some fossil traces as reflecting a depth related increase in 

44 
foraging efficiency. The simple descriptive use of lebenspurren will not be considered 

here since it is somewhat devoid of ecological relevance. 

Unfortunately, benthic surveys of lebenspurren have proven of little value for 

either population estimation or behavior studies. As will be discussed shortly under the 

topic of bioturbation, the deep-sea floor is exposed to animal disturbance far longer than 

the shallow bottom due to very low sedimentation rates. This exposure is so long, in fact, 

that the animals can completely homogenize the sediment layer they occupy. As a 

consequence, animals both make marks and erase marks by their activities . Wheatcroft et 

al . (1988) have treated this make/erase relationship with mathematic formality. 

The limited utility of lebenspurren studies was well demonstrated in a MMSfunded deep baseline survey (Gallaway et a1 .1988) . The failure of this effort is easily 

understood. The count of lebenspurren in a photograph is a snapshot in time as well as 

space reflecting the contributions of both trace making and trace erasing at that place and 

time. Logically, trace making increases in some simple manner, possibly a linear 

relationship, with the extent of animal activity on the sediment surface . The persistence 

of these traces, however, must decrease as more and more new traces obliterate the old. 

As a result, the number of observed traces by itself provides ambiguous information 

about the extent of animal activity . A few traces may indicate either low populations or 

very high populations . Indeed, traces only become informative if the population of trace 

makers and erasers is known. Obviously, if you know that, the study of traces is 

unnecessary. 

The behavioral utility of lebenspurren in the deep sea has been extensively 

considered by Kitchell (1979) and Kitchell et al .(1978a, 1978b). Predictions from the 

Seliacher model of foraging efficiency were not supported in either bathymetric surveys 

or trophic surveys under polar ice cover. It was concluded that feeding is a multifactored process, the efficiency of which can not be judged from tracks and trails . 

Bioturbation 

While lebenspurren studies look at discrete structures made by animals, 

bioturbation studies consider biological activity in sediments as an homogenizing 

process. Early in the use of microfossils in deep-sea sediment, it was recognized that 

animal mixing blurred the fossil record, and some crude models of mixing developed. 

Guinasso and Shink (1975) formalized these models as analogous to Fickian diffusion 

and started the practice of describing bioturbation as a dimensionless mixing coefficient 

operating through a sediment mixed layer of a specific thickness. Ecologists have always 

been somewhat dissatisfied with the lack of biological reality of these models 

(Wheatcroft et a1 .1988), but they have proven suitable in chemical tracer studies and have 

been extensively developed (Boudreau 1986a, 1986b) . 

So far, the importance of bioturbation studies in the deep sea and shallow 

environment has been in the context of pollutant fates rather than ecology . In the 

simplest models of pollutant incorporation into bottom sediments, the pollutant moves 

down into the sediment at a rate determined by diffusion and sedimentation. Both of 

these processes are very slow, especially in the deep-sea. If these models were correct, 

then most pollutants would be limited to the top few millimeters of mud. Bioturbation 

45 
models show that mixing by animals far exceeds sedimentation or diffusive influx and 

can spread pollutants through a mixed layer of sediment typically 10 cm thick. 

Therefore, to predict the distribution of a pollutant in a biologically active bottom, it is 

necessary to determine both the mixing coefficient and mixed layer depth. These are 

estimated from chemical gradients in the sediment with supportive sediment structure 

data. 

2.5 .3 MMS Management Needs 

For the most part MMS has been correct to remained focused on species-level 

survey while being criticized for not taking a process-oriented approach. This is because 

in shallow water it is not clear how impacting activities and natural processes interact . In 

deepwater, however, a process approach may be much more useful . The fact that most 

deep-sea animals are deposit feeders depending on detritus influx for food suggests a 

simpler trophic structure. In addition, the simplicity of this system suggests that 

interference with them may be a major impacting activity . With respect to influx, a full 

description of a deep habitat should include time series sediment trap studies. 

The study of tracks and trails is too detailed and too information poor to have 

great management utility as a measure of benthic processes or fauna. On the other hand, 

bioturbation studies that usually focus upon gradients of chemical tracers are on the 

wrong time scale to be of much use. Management simply needs a means of determining 

the extent to which the sedimentary environment is biologically structured. This might 

be most easily done in an experimental setting. Such a measurement might gently 

smooth the surface of the sediment and then employ image technologies to provide a 

times series description of the reestablishment of microtopography. 

2.6 Case Studies 

2.6 .1 Introductory Summary 

Development of management strategies appropriate for deep oil and gas 

development can only benefit to a limited degree by the examination of prior work 

undertaken for regulatory purposes. The limitation of previous work must be stressed, 

since the planned activities were very different than oil and gas development, and 

projects were usually terminated prematurely when the regulatory need vanished. Deep 

regulatory studies have been undertaken in the US in conjunction with dredge spoil 

disposal, hazardous waste (nuclear and chemical) disposal, manganese nodule mining, 

polymetallic sulfide mining, and oil and gas development. In the following sections 

mining and hazardous waste dumping are reviewed and the overall relevance to oil and 

gas management considered . In addition, the case of the proposed scuttling of the oil 

storage facility Brent Spar is considered as an example of a poorly executed oil industry 

deep activity . 

Of the mining studies, nodule mining provides some excellent guidance for future 

oil and gas relevant environmental work. 

" Massive impact was to be accepted in some areas balanced by total protection 

from impact in large-area preserves. 

46 
The studies carefully considered the unique aspects of deep-sea ecology and 

focused upon fauna and plume effects on detritus influx . 

Industry and regulators undertook cooperative environmental research during 

large-scale trial mining programs. 

Industry undertook some environmental research on its own initiative . 

The dumping studies are somewhat less value in the context of planning oil and 

gas development. 

" High hazard studies, typified by radioactive waste disposal, focussed on human 

health issues rather than environmental impact. 

" Low hazard studies, typified by sewage sludge dumping, initially structured tasks 

around inappropriate models. Thus, little relevant information was gathered 

prior to cessation of dumping. 

In each case considered the studies of deep-sea environmental impact were 

terminated prematurely due to a shift in government priorities . Deep ocean mining is non 

economic and dumping has been effectively banned. While it may seem appropriate that 

regulatory agencies have ceased extensive deep-sea work, this cessation places the oil 

and gas manager in a sensitive situation . There is a growing need to dispose of hazardous 

wastes, and there remains an interest in renewed ocean disposal . Any industrial use of 

the deep-sea may be seized upon by the advocates of ocean disposal as justification for 

renewal . The oil and gas industry and its managers should carry out the needed 

ecological research fully aware that other industries will use the results for unintended 

purposes. 

2.6.2 Deep Ocean Mining 

Of all proposed deep-ocean uses, mining is most similar to oil and gas 

development since it is involves a similar industry and lies under a related regulatory 

umbrella. It is quite different, however, in that mining severely impacts and permanently 

alters large areas of seafloor habitat. By comparison, the impact footprint of oil and gas 

is small and temporary under existing decommissioning regulations. Two deep mining 

activities have received varying degrees of interest . Nodule mining of the central Pacific 

is the most familiar topic. However, MMS' deep activity has already included the less 

known subject of polymetallic sulfides . The US studies undertaken to look at 

environmental impact of nodule mining are especially noteworthy. Even though 

international sea floor was involved, the US Congress issued restrictive regulations. With 

the National Oceanic and Atmospheric Agency (NOAA) as lead, scientific consensus as 

to the most important studies was developed and then selected studies carried out. 

Studies took advantage of industry proof-of-method projects and involved international 

cooperation. 

Ocean Mining of Manganese Nodules and Polymetallic Sulfides 

Manganese nodules were discovered during the voyage of the HMS Challenger. 

The dense nodule aggregations of the central north Pacific first received economic 

interest when cold-war economics dictated that the US move toward self-sufficiency in 

strategic metals . Mero (1952) is first credited with proposing manganese nodules as a 

viable oar for manganese, cobalt, nickel, and copper . By the 1970's six international 

47 
consortia had been formed to prospect and develop mining and refining technologies 

(United Nations 1985). Several patents were subsequently issued for different mining 

methods, all of which depended upon gouging the seafloor down to 45 cm in the 

sediments, separating nodules from sediments, and returning just the nodules to a surface 

ship. 

Three consortia, Ocean Mining Association (OMA), Ocean Management Inc . 

(OMI), and Ocean Minerals Corporation (OMC) pursued development to the point of 

trial mining at 1/4 to 1/5th commercial scale during the 1977-79 period . OMA tested 

their system in 1977-78 aboard the Ocean Miner II producing 25-70 tons of nodules/hr 

with an overall haul on the best trial of about 500 tons. During a November 1978 trial, 

NOAA monitored the environment as part of the DOMES (Deep Ocean Mining 

Environmental Studies) program. OMI used a converted drill ship, the SEDCO 445, for 

hydraulic mining trials in 1978, producing about 800 tons of nodules. OMC successfully 

tested their system in that same year, employing the heavy lift ship GLOMAR 

EXPLORER, the Central Intelligence Agency (CIA) vessel which used nodule mining as 

a cover activity for recovery of a sunken Russian submarine. 

Since widespread public concern over environmental degradation was a product 

of the 1960's and 70's, plans to exploit the seafloor were closely paralleled by concerns 

about environmental impact (Gerard 1976). Barkenbus (1979) has characterized the 

prevailing environmental views about deep-sea mining at the time as ranging from 

confidence that there would be no impact up to fear of catastrophic damage. This review, 

however, found no literature taking this latter extreme view. Indeed, environmental 

concern, as evidenced by the literature was quite moderate. The National Research 

Council (NRC 1975) called for assessment of impact and monitoring during the 

development of technology by industry . There were no moves to block development 

prior to better environmental understanding. 

International and Federal Policy Advocacy for Stable Reference Areas 

In the 1970's the US participated in the United Nations with respect to (LOS) 

Conference, expressing fundamental reservations about the provisions for seabed mining 

contained in Part XI. So as to provide site security for US companies without the LOS, 

the US Congress passed in 1980 the Deep Seabed Hard Minerals Act as an interim 

measure. It assigned both licensing and environmental regulation to NOAA. 

Internationally, the Preparatory Commission of the Law of the Sea registered claims for 

Russia, Japan, China, France, India and Interocean Metals . Conflicting overlaps were 

settled through negotiations . The major US concerns about the LOS provisions were how 

seafloor activities would be administered and how the resources of participating 

companies might be directed toward non participating countries and corporations . 

With respect to seafloor mining, both LOS and the US Deep Seabed Hard 

Minerals Act called for the setting aside of preserves which would not be mined. Termed 

Stable Reference Areas (SRA's) (Post 1983). These areas were to be large and fully 

representative of the habitats to be destroyed by mining. A key difference between LOS 

and US implementation of SRA's was that LOS gave designation and study responsibility 

to industry, while US law gave the responsibility to NOAA. In 1982 NOAA received the 

first applications for nodule exploration from four US consortia: Ocean Minerals 

48 
Company, Ocean Management, Inc ., Ocean Mining Associates, and the Kennecott 

Consortium . All four licenses were granted in 1984 permitting 10 years of exploratory 

activity . Pursuant to Section 109(d) of the Deep Seabed Hard Minerals Resources Act 

(P.L . 96-283) and 102(2)(c) of the National Environmental Protection Act, the 

administrator of NOAA submitted an Environmental Impact Statements limited to the 

potential effects of exploration. The EIS process was greatly complicated by the issue of 

international waters and the evolving law of the Sea treaty . The sites of the four licensees 

were originally kept confidential . Following international resolution of overlapping 

license areas claimed by foreign programs, and US the revised coordinates were made 

public . NOAA argued that the changes in coordinates did not alter the conclusion of no 

significant impact, and supplemental EIS's were not prepared. 

Establishment of SRA's is a prudent management strategy that trades assured 

protection of a bit of seafloor for permitted impact upon similar habitats elsewhere. The 

concept of settling aside areas of the seafloor as preserves was an effective means of 

dealing with the limited level of understanding about the deep environment while not 

calling for a cessation of industry development. It was envisioned (Anonymous 1981) 

that research comparing impacted and preserved bottoms could be carried out in parallel 

with industrial development in permitted tracts . As ecological understanding increased, 

industry procedures could be modified so as to minimize environmental impact . 

Environmental studies of the effects of deep-sea nodule mining fall into three 

broad categories: NOAA's initial Deep Ocean Mining Experiments (DOMES), NOAA's 

final studies supporting the Stable Reference Area (SRA) concept, and industry studies 

supporting license application and EIS submission. Due to severe technical and logistical 

restraints, these three components tended to build upon and cooperate amongst one 

another. There are no currently active studies. NOAA concurs with the assessment that 

nodules have no economic value in the foreseeable future (Hoagland 1993, NOAA 1989, 

1994). 

The Project 

DOMES, the Deep Ocean Mining Environmental Study (NOAA 1982, Amos et 

al . 1982) was the initial project which considered the full range of possible mining 

impacts from the benthos up to the ocean surface. By itself, this is not an especially 

noteworthy project. However, it led to subsequent work on deep-sea stable reference 

areas. Contributing to the weakness of the DOMES project is a peculiar focus. Oddly, it 

expended considerable effort on the upper ocean where it was thought that sediment 

plumes might impact primary productivity . However, box core surveying was conducted 

(Hecker and Paul 1979). The conclusion that mining would destroy fauna in and near the 

path of the mining device, was arrived at more from the examination of bottom photos 

(Oztergut et a1 .1981) taken before and after trial mining (technologies reviewed by 

Smale-Adams and Jackson 1978) than from faunal samples. A small-scale follow up 

study was inconclusive . Although lacking a preliminary baseline and having no means of 

assessing the extent of plume effects, a descriptive post mining study, the ECHO I 

Expedition, was supported by NOAA in June 1983 (Spiess et a1 .1984) . 

49 
The SRA Concept Studies 

The requirement that SRA's duplicate the environment to be subject to mining 

dictated that SRA's be located in close proximity to mined areas. The initial criterion for 

citing thus became determination of how far from a mining operation the near-bottom 

sediment plume has an effect (NRC 1984) . The design of a controlled dose sediment 

exposure experiment underwent considerable discussion, with initial specifications for a 

mining simulator being developed by The Glosten Associates of Seattle (1987) . 

The most concisely stated and conceptually well founded environmental concern 

about deep-sea mining was that the downward flux of even small amounts of resuspended 

material in a mining plume could greatly upset faunal foraging . This idea was first 

articulated in correspondence by Drs. Peter Jumars and Robert Hessler and later 

elaborated in the open literature (Jumars, 1981) . The essential parts of the argument are 

as follows. Most biodiversity in the deep nodule province is represented by small 

polychaetes and crustaceans which feed directly upon a very thin dusting of labile carbon 

in settling detritus, or upon bacterial biomass exploiting more refractive carbon buried in 

the sediment. Net inorganic sedimentation in this region may is very low. Given such a 

low natural sedimentation rate, even miniscule amounts of old sediment dropping out of a 

mining plume may be experienced as a dramatic dilution of the labile carbon supply. If 

the fauna has developed foraging strategies adapted to natural rates of influx, then this 

artificially high sedimentation regime may prove deleterious . 

The initial concerns that mining impact beyond actual mining vehicle track tract 

would be due to acute and chronic burial were developed in detail by Craig Smith and his 

colleagues (Smith et al . 1988). Employing a clever model that determined the amount of 

burial needed to cut off observed levels of oxygen consumption, it was estimated that 

approximately 4 cm of acute burial would cause asphyxiation of the fauna. Effects of 

acute burial were experimentally examined at bathyal depths off San Diego using cores 

dosed with a 1 and 4 cm sediment cover. Cores were emplaced, dosed, and harvested 

after six days by a remote vehicle. Unfortunately, logistical problems limited both the 

number of replicates and the duration of the study . Statistical test of abundance changes 

associated with degree of burial could find no impact . However, the investigators 

strongly suspected that the short incubation prevented actual effects from being detected . 

In support of this contention, it was noted that fauna in cores with 4 cm added sediment 

showed no sign of repositioning upward, while such upward migration had occurred in 

cores with only 1 cm of added material . 

Industry Studies 

In any potentially impacting activity there is an inherent conflict between 

developers and regulators. While there may be regulatory mandate that industry carry out 

pre-development impact assessment, such studies often suffer from the understandable 

fact that industry seldom invites regulation. As a result, the studies are seldom more than 

a cursory look at the fauna. Such a mandated study is reflected in the license application 

filed by the Ocean Minerals Company (OMC 1982) in compliance with Public Law 96-

283 and NOAH rules pertaining to such applications as published in 46 Federal Register 

45985-919, provides insight into environmental concerns. It was proposed to strip 

50 
nodules from the seafloor with a self-propelled vehicle connected by flexible link to a 

relatively rigid pipe running to the surface vessel . A miner as large as 10 m wide and 

sweeping over lm of bottom a second would be used (Welling 1981) . The license gave 

minimal attention to collector and plume effects . While it was acknowledged that NOAA 

identified these as concerns, impact prediction was not attempted. It was commented that 

impact could not be assessed until actual mining and environmental monitoring had 

begun. 

Supportive studies included box core samples for macrofauna and photo/video for 

megafauna. Recolonization experiments were anticipated in conjunction with mining 

trials . Reports on megafauna both photographed and recovered during nodule collecting 

makes the point that there appeared to be no fauna characteristic of the nodule field, just 

representatives of a ubiquitous regional fauna. No infauna results have ever been 

reported . Megafaunal results have been published (Foell and Pawson 1986). There was 

no use made of survey data in the license application. 

Polymetallic Sulfide Mining 

Polymetallic sulfides are ore bodies created when metal-rich hydrothermal fluids 

are emitted at the seafloor (Francheteau et al . 1979). In 1983 MMS issued a draft 

environmental impact statement (DEIS) preparatory to a planned federal mining lease 

sale for US EEZ sea bottom on the Gorda Ridge off Oregon and Washington. This DEIS 

was issued in an environment of unclear regulatory authority between the departments of 

Commerce and Interior and an environment of no serious industry interest . Adding to a 

poor public acceptance was the fact that the DEIS was produced quickly and depended 

too heavily on inapplicable ecological studies of nearby seafloor but very dissimilar 

environments . A multi-participant group, the Gorda Ridge Technical Task Force, was 

established to address these problems (McMurray 1986) . 

Following an initial assessment of knowledge (Boudrais and Tagon 1986), a 

cursory benthic survey of the actual planned lease site was supported by the Task Force 

using DSV ALVIN to make bottom photographs and videos (Carey et a1 .1986) . The 

quality and spatial control of the images did not support detailed analysis . However, an 

interesting discovery was made. Contrary to the generalization that deposit feeders 

predominate, sessile suspension feeders were common. Due to a lack of industry interest, 

there was no subsequent study. 

2 .6 .3 Ocean Dumping of Hazardous Wastes 

The deep-sea has been used as a dumping ground for many decades due to its 

remoteness and presumed lack of resource conflicts (Palmer 1988, Simpson et al 1981). 

Dumping has included dredge spoils (Pequegnat 1983b), industrial wastes (Pearce et 

a1 .1979, Vaccaro et a1 .1981), sewage sludge (Walker and Paul 1989), and munitions. Of 

these, munitions' dumping is shrouded in mystery. A glance at any navigational chart 

shows numerous sites on the continental slope and deeper marked "Explosives Dumping 

Area" . In the case of the Gulf of Mexico, these sites are located on seafloor subject to 

leasing by MMS. Information of designated munitions sites is scant. The Oceanographer 

of the Navy (1972) released a summary of oceanographic conditions at "number sites", 

where munitions-laden ships were scuttled . The data behind these studies seldom 

51 
consisted of more than a photographic survey (Carey et a1 .1973) . 

Deep Water Dumpsite 106 

The most extensively studied and published environmental studies are those of the 

multi-use deepwater dumpsite DWD 106 off the coast of New Jersey . While this site has 

received municipal waste, military radionuclide waste, and industrial waste, the work 

dealing with sewage sludge is of greatest general management interest (Walker and Paul 

1989) . Prior to the effective imposition of the ban on such dumping, coastal residents of 

the New York Bight area perceived that near-shore sewage and waste dumping were 

producing unacceptable impacts on human health, environmental aesthetics, and ocean 

ecology. Political action arising from this public concern produced the Ocean Dumping 

Ban Act (ODBA) that was to have stopped sewage sludge and industrial waste dumping. 

However, the affected sewage programs had the conditions of the ODBA set aside by a 

New York District Court in 1981 . With the ban in suspension, the US EPA did close the 

nearshore dump site on the basis of environmental degradation and designated the DWD 

106 as the permitted site for sewage disposal in 1984 . 

The shifting of the sludge to a deep water site did nothing to placate public 

concerns. Although never well substantiated, there were reports of increased fish 

diseases. Adding to public distrust in the wisdom of dumping deeper was the adoption of 

a NOAA monitoring program structured around an obviously inadequate plume 

dispersion model which predicted that no dumped material would reach bottom. In 

effect, NOAA studied the wrong part of the environment. Ultimately, the terms of the 

ODBA were applied to DWD 106 and sewage dumping halted entirely . The banning of 

sewage sludge and industrial wastes into the oceans by the Ocean Dumping Ban Act 

(ODBA) passed in 1977 and amended in 1988 stands out as the most dramatic case of the 

U.S . government regulating deep ocean environmental impact. Rather than just 

prohibiting an anticipated activity, this ban actually stopped ongoing sewage sludge 

dumping at Deep Water Dump Site 106 in the North Atlantic. This action forced 

adoption of far more expensive sewage disposal options for New York City and 

surrounding communities. While there was a substantial research effort associated with 

this ban and concern about deep ocean environmental impacts at DWD 106, review of 

testimony and questioning at Congressional Hearings suggest that concerns over deep-sea 

ecology played a minor role (U.S. House of Representatives 1992). 

Long-term monitoring of DWD 106 is a major programmatic focus of the NOAA 

Undersea Research Program at Rutgers University (F. Grassle per. com). This work 

involves international scientific cooperation and participation by the United State 

Geological . Survey. Much of this monitoring focuses on chemical tracers (Bothner et 

a1 .1992, Takada et a1 .1992, Van Dover et a1 .1992) along with a high resolution 

description of the physical environment ( Butman et a1 .1992, Robb and Grassle 1992). 

Several recent projects were published in 1996 and show the mixed result that all effects 

studies tend to show. A review of earlier work and a summary of results been presented 

by Hunt et al . (1996) . Fish populations did not show conspicuous impact (Musick et 

a1 .1996), and disease in commercial species could not be attributed to site effects due to 

confounding effects (Ziskowski et a1 .1996) . However, contaminants did seem to enter 

the pelagic nekton (Zdanowicz et al . 1996), but were species specific in benthic 

52 
megafuana. Some species showed no contamination concentrations (Steimle et a1 .1996), 

while others did (Sennefelder et a1 .1996) . 

Nuclear Waste Disposal 

The proliferation of the nuclear industry following World War II for electrical 

power and weapons took place with full government awareness that technologies did not 

then exist for safe long-term disposal of radioactive waste. Protected by secrecy, 

weapons wastes were disposed of in the ocean as a simple extension of ocean dumping. 

More exposed to scrutiny, nuclear power facilities were built with on-site storage 

capacity awaiting better options. By the mid 1960's ocean dumping was being viewed as 

unacceptable, and progress towards better disposal options were not appearing. Thus, the 

problem was growing. 

The concept developed in the Sandia Labs Subseabed Disposal Program was a 

multi-barrier containment program . Wastes would be chemically and structurally 

processed to solidify and stabilize them, then encased in a vessel capable of containment 

for many 1000's of years. These vessels would then be buried in about 20 m of seafloor 

clay in central regions of the ocean at depths greater than 4km of water. Five technical 

and one policy arguments were initially put forward in favor of the subseabed disposal 

option. 

" The deep-sea floor in the middle of continental plates is a geologically stable area. 

" The clay layers in these regions affords a good barrier against seepage of nay 

materials that might leak from containers . 

" These areas are low in other resources and the biota is small and rare . 

" Sediment geochemistry in these areas is predictable. 

" Even if something does leak and escape containment, dilution still affords a high 

degree of protection. 

" Being in international waters it could be a disposal option open to all nuclear 

countries. 

Subseabed Disposal Program 

The SDP was divided into six task areas : site assessment, barrier assessment, 

environmental studies, engineering, systems, and regulatory issues . The ecological 

studies of the SDP are distinct from other environmental studies in two ways. Firstly, 

they had not progressed to a baseline study since the disposal method was in its earliest 

developmental stages . Secondly, most of the research could be considered as processoriented . Rather than carry out traditional research aimed at determining population and 

distribution parameters, the research was driven by ecological models. Ecological 

activities of the SBD study revolved around two models of ecological function, a multicompartment food web model (MFM) and a Deep-Sea Carbon Model (DSCM). The 

former sought to prediction movement of released radionuclides from the buried 

repository through 16 model compartments. The latter was restricted to the cycling of 

organic carbon in the bottom and near-bottom environment. Both models lumped fauna 

into fairly coarse groups either by position (epibenthic, infauna, pelagic, etc) or size 

(meiofauna, macrofauna, etc) . Therefore adequate research had only to determine the 

biomass in these model compartments and the types and degree of exchange between 

53 
compartments. Species inventories, diversity, etc. were superfluous in this context. 

Seabed Disposal of Contained Low-Level Wastes 

Unlike programs seeking to develop disposal schemes like the SDP discussed 

above, and nuclear submarine disposal discussed below, EPA programs were undertaken 

to establish regulations that would control permitting for disposal . The starting point for 

such studies was International Atomic Energy Agency (IAEA) site criteria suggested to 

the London Dumping Convention (Table 2 .6). Stated quite simply, small sites could be 

established on the seafloor greater than 4000 m depth in regions of oceanographic 

stability, no possible use conflict, limited biological activity, and at locations where 

operations were practical . Stabilization, containment, and emplacement were not 

specified. 

Federal Policy History 

The SDP is an especially interesting case since the program was initiated after the 

ban on ocean dumping. Thus, SDP faced three stiff policy challenges . First, the program 

would have to show the ocean option to be superior to other options. Second, the 

superiority of the ocean option would have to be so great as to justify reversal of a ban. 

Or, as a last-resort, the technology of the vastly superior ocean option would somehow be 

exempt from the ban . None of these proved to be the case. 

While the Nuclear Waste Policy Act (NWPA) authorized study of the subseabed 

disposal option, no program could have been put in place due to restrictions contained in 

MPRSA (the Marine Protection, Research, and Sanctuaries Act of 1972 (Public Law 92-

532)). In Title I, Ocean Dumping Prohibited Acts, Section 102, the issuance of permits 

by EPA for radioactive dumping is specifically prohibited . Thus, had the studies lead to 

the recommendation by DOE that subseabed disposal begin, Congress would have to 

have amended the act, probably giving EPA specific approval to permit such activity and 

NOAA authority to monitor the sites. Internationally, a similar exemption from the 

prohibitions of the London Dumping Convention would have had to be arranged, and 

international accords adopted as to permitting and monitoring. 

In 1986 the study of the subseabed disposal option was halted for policy reasons . 

In effect, it was decided by DOE and congressional committees that the US should 

vigorously pursue only the land-based disposal options. Thus, an operational program 

with its regulatory structure was never implemented. Prior to this premature cessation, 

DOE began funding in 1974. This task was then reaffirmed and expanded under 

authority of the NWPA, Nuclear Waste Policy Act of 1982 (Public Law 97-425), Sec . 

222 Reassert on alternatives for the permanent disposal of high-level radioactive waste 

act. The initial timetable called for a preliminary assessment in 1976, progressing though 

four stages to a demonstration project in the year 2010. By 1985 the U.S . program was 

well into phase two of research associated with concept feasibility at its maximum. 

Annual funding had reached approximately $13M/year, and about $116M had been spent 

on the life of the project. 

54 
Bettis Project 

The Bettis Project was undertaken to determine the feasibility of deep ocean 

disposal of defueled, decommissioned nuclear submarines as they passed their effective 

operational life . Activated metals in the submarines' nuclear systems would be the 

primary radioactive material and are classed as low-level wastes . The Navy envisioned 

two disposal options. The deep-sea option consisted of removing high-level material, 

placing miscellaneous low level materials in the steel pressure vessel for containment, 

then sinking the sub in a deep-water site within the US EEZ. Alternately, the land option 

consisted of cutting up the sub, placing nuclear waste material in a sealed section, and 

burying that section at a land-based site near Handford Washington. 

The Navy's desire to dispose of material in US controlled water added complexity 

to the International Atomic Energy Agency (IAEA) submission to the London Dumping 

Convention on acceptable site criteria (Table 2.6). These criteria tended to favor sites in 

international waters far from land. Thus, part of the project was finding EEZ sites that 

otherwise met the criteria. Compromising the Navy's desire to be in the US EEZ with 

IAEA criteria resulted in identification of two Atlantic and two Pacific . In the Atlantic 

were the Antillies Study area off Puerto Rico and the U.S . Virgin Islands and the Hatteras 

Study area off the Carolinas. In the Pacific, a Western-Northern site lay off Cape 

Mendocino in Northern California and a Western-Southern site seaward of San Diego. 

Table 2 .6 . IAEA Categorized Criteria for Deep-Sea Nuclear Waste Disposal Sites 

I. Criteria Based on Ecological Concerns 

1 . Sites should be between 50 North and 50 South. Thus avoiding the highly productive polar 

regions along with associated operational problems . 

2. Depth at the site should be more than 4000 m. Thus being in the least productive and most 

homogenous part of the marine ecosystem. 

3. Sites should be remote from the continental margins. Thus avoiding the biological activity and 

biological resources closer to land . 

II . Criteria Based on Abiotic Aspects of the Environment. 

1 . Sites should be away from areas containing active geological phenomena such as volcanoes, 

which would be unsuitable . Thus avoiding geologically unstable regions. 

2. Sites should be away from areas, such as marine canyons, which have a high rate of exchange of 

the deep waters with surface layers of an adjacent continental shelf. Thus avoiding rapid 

transport of spilled wastes to man. 

3. Bottom current shear stress should not exceed critical erosional shear stress . Thus avoiding 

resuspension . 

4. Sites should be away from areas of intense mesoscale eddy activity. Thus avoiding rapid 

transport to man. 

III. Criteria Based on Conflicting Usage. 

1 . Sites should be away from areas of potential seafloor resources. 

2. Sites should be away from cables in use. 

55 
Table 2.6 Continued . 

IV. Criteria Based on Practicality of Operations. 

1 . The area of a site should be defined by precise coordinates, with an area as small as 

practicable, but no larger than 104 km' . 

2. Sites should preferably be in areas covered by navigational aids . 

3. Sites should be chosen for convenient conduct of operations and to avoid, so far as possible, 

the risk of collision with other traffic and undue navigational difficulties . 

General oceanographic survey programs were initiated at the study areas with a 

strong emphasis upon geological and physical oceanography. The possibility of deep 

nekton as a connection to human food chains was considered . No effective study of biota 

or of possible biological effects was ever undertaken. A draft EIS was filed by the Navy 

for the ocean option . That document contained no serious discussion of ecological 

impact. It did however, attempt to develop a worst-case model for human exposure via 

the foodweb. While, the model may have been conceptually sound, the lack of data 

supporting its assumptions and parameters rendered it useless. 

2 .6 .4 A Flawed Proposal to Scuttle an Oil Storage Facility 

The Brent Spar, a floating storage and offloading structure in the North Sea, was 

destined by its owner in 1991 to be scuttled in deepwater . The plan lead to heated public 

debate and strong opposition by Greenpeace (Rice and Owen 1999). The Brent Spar 

controversy in the United Kingdom is particularly relevant to deep ocean oil and gas 

development in the United States for four reasons . 

" Although not directly related to deep development, the proposed disposal in 

deepwater was an activity of the offshore oil and gas industry . 

" The superficiality of the environmental studies and the failure of both government 

and industry to insist on an adequate program utilizing the best available 

scientific talent are a case of exceptionally poor management. 

" When the general public's attention is directed by advocacy groups and the press, 

very strong negative sentiment can arise despite the deep environment' s 

remoteness and unfamiliarity. 

" The Brent Spar debate persists in the European scientific community and will 

greatly influence developing standards of completeness and quality for deep 

management studies. 

Since Rice and Owen (1999) have provided a detailed account of the Brent Spar 

decommissioning, only a brief sketch will be provided here. In 1991 Shell UK decided 

that the Brent Spar should be decommissioned . Over the next two years, feasibility 

studies were conducted by university-based contractors with a history of industry and 

government work but no deep-sea experience . Most were engineering studies. Two could 

be considered oceanographic, the Aberdeen University Research and Industrial Services 

(AURIS) Report (AURIS 1994) and the Metocean Report (1993) . In late 1994 a field 

program was undertaken, and a final request for disposal in deepwater was submitted just 

three months later in Dec. 1994. The advocacy group Greenpeace seized upon negative 

sentiment for major oil companies, exaggerated the contaminants issue, and mobilized 

public sentiment against ocean disposal. In the course of subsequent debate and review, 

56 
the factuality of claims declined in importance and the poor implementation of the 

permitting process became the focus of argument. 

The debate about deepwater decommissioning became so heated and political that 

a review was initiated by the House of Lords Science & Technology Committee. The 

primary non-government reviewing body was the Natural Environment Research Council 

(NERC). The report of the Scientific Group report on Decommissioning Offshore 

Structures (NERC 1996) concluding that the procedure for arriving at a Best Practicable 

Environmental Option (BPEO) for the Brent Spar was poorly executed and that fore 

drawn conclusions had been advocated without sufficient inquiry and participation by 

interested parties. The report did not, however, condemn deepwater disposal in general 

or specific disposal of the Brent Spar. 

The BPOE 

The BPEO Assessment concluded that deepwater disposal was preferable on 

grounds of: (1) reduced technical risk ; (2) reduced safety risk to the workforce; (3) 

insignificant environmental impact, (4) and total cost. Preparatory to disposal the Spar 

would be made safe and cleaned of accessible hazardous materials for disposal onshore. 

Three potential sites in U.K. waters deeper than 2000 m were identified by the Scottish 

Office Agriculture and Fisheries Department (SOAFD) as potentially suitable for the 

disposal of redundant offshore structures : North Feni Ridge, Rockall Trough, and 

Maury Channel. Consistent with 1991 Oslo Commission Guidelines for the Disposal of 

Offshore Installations at Sea an 'impact hypothesis' was prepared for the Brent Spar. 

Three sinking scenarios were ranked by likelihood and a dilution argument but forward to 

support the conclusion that impacts would be minimal and acceptable under all three 

scenarios. A field study was conducted by Shell Exploration and SOAFD in August -

September 1994, to determine site suitability and provide a baseline for monitoring. The 

published results of this study (Rudall Blanchard Associates Ltd. 1994) were generic and 

developed from the literature rather than data analysis. 

Scenario 1 . Most Likely - the spar would sink intact to the sea floor and remain intact 

after impact. Contaminants would be slowly released . 

Scenario 2 . Less Likely - storage tanks would be damaged during sinking or impact 

with an initial rapid release of contaminants at the seafloor 

followed by chronic discharge associated with corrosion. 

Scenario 3 . Least Likely - storage tanks would be damaged and discharged near the 

surface followed by chronic discharge associated with 

corrosion at the seafloor 

Official Post Hoc Criticism of the BPOE 

From the US management perspective, the most notable aspect of the BPOE 

review is that it occurred at high levels in response to great public pressure rather than as 

part of a routine process. The greater public participation in the US EIS process makes 

such an extraordinary review less likely . The report (NERC 1996) contained twenty nine 

conclusions. Five are of special interest in the context of deep oil and gas management in 

the US. 

57 
" Scientific assessment of ecological impact is only one factor is accessing the 

suitability of a disposal plan. Allowing or banning any waste dumping 

involves social, economic, ethical, and aesthetic considerations . 

" Cumulative rather than acute impacts of the disposal of offshore oil installations 

must be assessed. 

" Public acceptability must be considered in evaluating future marine 

environmental impact assessments. Relevant documentation about disposal of 

the Brent Spar was confidential too long. 

" Onshore versus offshore options should consider general considerations such reusing and re-cycling . 

" The deep sea is biologically rich, and impacts are not yet predictable in that 

environment. Study of natural and man-made analogues might prove 

beneficial . 

Criticism from the Scientific Community 

As part of the review of the Brent Spar controversy the British Scientific 

community issued two important comments that stressed the inadequacy of the studies 

undertaken. The first was in the form of an official statement by the Institute of Biology, 

British Ecological Society, and the Linnean Society of London. The second was an open 

letter expressing the opinions of the scientists working on the ecology of the Rockall 

Trough. The Rockall Trough studies have been one of the most scientifically productive 

studies of the deep sea ever undertaken. 

The 15,000 member Institute of Biology submitted comments along with its 

affiliated societies, the British Ecological Society and the Linnean Society of London. It 

was concluded that deep-sea disposal should be included amongst the Best Practicable 

Environmental Options (BPEOs) considered for the disposal of North Sea oil and gas 

installations, but only after a cradle-to-grave resource analysis has been conducted for 

each option . Where costs and benefits between deep-sea disposal and on-shore 

dismantling are comparable, the precautionary principle should prevail in favor of 

dismantling. In the event of deep-sea disposal long term monitoring of the site is 

required . Specific rephrased recommendations included : 

" Deep-sea disposal should be considered as an option when facilities are first 

constructed so as to minimize impacts and costs. 

" The BPEO process should seriously consider more than a single option and make 

the details public during the process. 

" While there is no evidence that deepwater disposal of something like the Brent 

Spar will have unacceptable environmental impacts, there is no evidence that 

it will not. The question remains open. 

" There are moral and ethical dimensions to `environmental options' that cannot be 

defined in absolute terms. It is to be anticipated that moral and ethical 

opposition can arise regardless to the extent of scientific knowledge. To 

minimize such opposition, the disposal process must be considered very 

early; disposal of oil and gas installations must be considered in the design 

stage and approved by the appropriate authorities. 

" The basic BPOE process is adequate to address future disposal problems. The 

Brent Spar controversy arose from poor and secretive implementation. 

58 
In the deep sea, where uncertainties are many and data limited, it is not prudent to 

allow the operator to develop the BPEO. The best science needs to be 

applied. 

One of the single most damaging aspects of the studies undertaken as part of the 

Brent Spar decommissioning planning is that they made no use of the very considerable 

deepwater expertise of the Scottish Association for Marine Science. In effect, the British 

government paid for a study which specifically identified the Rockall Trough as a 

potential disposal site, yet totally ignored excellent and ongoing research in that area! 

Thus, once the controversy arose, the true experts convincingly identified the failings of 

the study. Indeed, it was the advocacy groups and the press that included the appropriate 

experts in the debate, not industry and government . 

Due to the comprehensiveness of an open letter to Greenpeace, it is excerpted 

here. The letter addresses three serious failings of the disposal plan. First, the plan is 

based upon ignorance of actual deep-sea species diversity. Second, the plan fails to 

consider deepwater fisheries. Third, the plan is based upon ignorance of deep-sea high 

energy events (benthic storms) . 

THE SCOTTISH ASSOCIATION FOR MARINE SCIENCE (SAMS) 

Dr Helen Wallace, 

Greenpeace, 

Canonbury Villas, 

London N 1 2PN 

28th July 1995 

Dear Dr Wallace, 

P.O . Box 3, Oban, Argyll, PA34 4AD 

We should like to express broad agreement with the "facts" . . . justifying Greenpeace's actions. 

We might add that scientists at SAMS with by far the greatest experience of deep-sea ecosystems in 

the Rockall Trough area . . . were never consulted for information. 

We would also like to point out additional deficiencies in both the Brent Spar Abandonment 

BPEO report that you copied to us, and the Brent Spar Abandonment Impact Hypothesis report (both 

dated December 1994) as known to us : 

(a) The assertion in BPEO under 8.3 .3 that "the deep ocean environment supports . . . a small 

range of species" . 

This is inconsistent with now widely reported data indicating very high diversity associated with 

the benthic fauna of the deep sea sediment. Indeed it is now becoming recognised that the biodiversity 

of the smaller invertebrates inhabiting the deep ocean sediments may rival that of the tropical rain 

forest (see Gage & Tyler 1996, Deep-Sea Biology, Cambridge University Press; Grassle, Maciolek & 

Blake 1991 in Woodwell (ed.) The Earth in Transition : Patterns and Processes of Biotic 

Impoverishment. Cambridge University Press, New York pp 384-359) 

In addition to this, knowledge emerging since the last major consideration of deep-sea dumping 

- that of high and medium-level radioactive waste in the late 1970's/early 1980's has indicated clearly 

that a whole range of biological rate processes ranging from the respiration of microbial communities 

and individual animals from fish to larger invertebrate 'megafauna', or the measured or inferred 

growth rates of small deep-sea invertebrates, may be much faster than previously supposed (see Gage 

1991 : Biological rate processes in the deep sea. Reviews in Aquatic Sciences 5: 49-100). Although 

not stated explicitly in either of the Reports prepared for Shell Expro, any disposal option based 

implicitly on characterization of the deep-sea as a "low-activity ecosystem" clearly now is highly 

inappropriate. 

59 
(b) The statement under 8.3 .4 that exploitation of the resources of the deep ocean (>1,500 m) is 

limited to laying of submarine cables and military activities fails to recognize the growth in deepwater fishing in recent years. 

While it is true to say that most of these fisheries take place at depths down to about 1,200 m 

there are some targeted fisheries which go deeper. There is little doubt that orange roughy has been 

fished to at least 1,800 m to the west of the British Isles. . . . There is also a need to question the rather 

simplistic views on deep-water fishes embodied in Section 5 .3 of the Brent Spar Abandonment 

Impact Hypothesis (December 1994). There is ample evidence that the continental slope west of the 

British Isles supports a high biomass and diversity of fish down to about 1,500 m. This biomass could 

never be supported by the benthic fauna and studies by SAMS, over the years, have shown the 

importance of benthopelagic and pelagic organisms in the diet of these fishes . This implies a much 

more efficient transport of food from the surface than that obtained from 'the downward flow of 

material derived from the surface water above (e .g. corpses, faecal pellets etc)'. The impingement of 

both the mesopelagic fauna on the slope is a rich source of food replenished from the surface by 

overlapping food-chains and diel vertical migration. 

We finally also question the justification for the three potential sites. The "North Feni Ridge" 

site is actually a deep hole, probably caused by current scouring, at the base of a seamount, the 

Rosemary Bank. Seamounts are where some of the targeted fisheries for species such as orange 

roughy occur. The "Rockall Trough" site located south of the Anton Dohrn Seamount, is very close to 

one of the main deep-water fishing areas. It is also an area which has been the subject of investigation 

by SAMS for many years. The Maury Channel site is the deepest of the three, but still close to 

developing deep-water fisheries in international waters . The arguments put forward in favour of the 

dumping option in the Scotsman (Dr M.V. Angel) and in the recent Nature editorial (vol . 375, p. 708) 

referred to abyssal sites. Slope sites have different characteristics and should be treated differently. 

(c) The apparent uninformed consideration in the Brent Spar Abandonment - Impact Hypothesis 

report of the effect of likely mesoscale high-energy events ("benthic storms") at the benthic boundary 

on the dispersal and transport of material into the water column mesoscale processes. 

Clearly such processes now need to be taken into consideration in modelling the dispersal of 

toxic compounds in deep water. The claim . . . that mean (presumably near-bed) current velocities 

were only I - 2 cm*sec 1 is not particularly useful in the present context where maximal velocities 

may be largely determining potential dispersal. We do not have available to us the Metocean (1993) 

report cited under 5 .2 .5 . so we are not able to assess the quality and appropriateness of the data on 

which that report was based. But we would comment that any general interpretation of relatively 

quiescent regime is at odds with the results from numerous long-term current meter time series 

undertaken by SAMS (then SMBA), the Institute for Oceanographic Sciences (IOS) and by MAFF 

(Lowestoft) at various sites in the Rockall Trough area . The picture of eddy kinetic energy (KE), the 

low-frequency peaks derived from mesoscale eddies in theupper water column, spun off strong 

surface flow or by storms, that emerges from the analysis indicate a very dynamic regime . . . It is also 

curious in view of what we have heard informally of the results from the SOAFD work for Shell 

Expro from their near-bed current meter time series data covering the period from the field work in 

1994 to April 1995. Apparently preliminary analysis of the data show sustained current peaks at the 

site where Brent Spar was to be dumped well over 50 cm sec's - indicative of severe benthic storms. 

Yours sincerely, 

John D. Gage, 

John D.M. Gordon 

2.6 .5 Summary of Lessons Learned 

In many of the cases presented above, deep-ocean field studies were terminated 

prior to completion due to changes in priorities or regulations during the extended life of 

60 
the programs. Therefore, the scientific utility of each is very limited. However, there are 

five very important policy points to be made. 

" Public Interest - There is a broad public sentiment for preservation of the ocean 

environment in some idealized un-impacted state. This public interest applies 

to all parts of the ocean, even the deep sea. Public opposition to deep-sea 

environmental impact must not be underestimated . 

" Government Regulation - As clearly evidenced both by the Law of the Sea and 

the US Seabed Hard Minerals Act. Environmental regulation will follow 

resource development no matter how deep or far offshore . The most easily 

decreed regulation in the face of limited ecological knowledge is protection 

through prohibition. 

" Ignorance in Unexpected Places - A historically dated and inaccurate wasteland 

view of the deep-sea floor persists even in the non-biological sub disciplines 

of oceanography. It is to be expected that deep-sea exploitation plans can 

progress to highly advanced levels in total ignorance of potential 

environmental consequences. 

" Narrow Focus - Rather than attack all topics about the deep sea, models or first 

principles have been used to narrow the focus of inquiry. In the case of the 

initial NOAA studies of DWDS 106, an inappropriate plume model wasted 

much effort . However, in the SRA studies for nodule mining, emphasis upon 

detritus influx served as a very good central theme. 

" Industry Participation - Deep-sea research is logistically expensive and its 

difficulty is compounded by the novelty of the technologies which may cause 

impacts. Therefore, environmental studies by managers and technological 

trial programs should be combined. 

2.7 Deep Survey Design and Methodology 

2.7 .1 Introduction 

It is the purpose of this chapter to review the design and execution of deep-sea 

data collecting methods, indicating which can be considered relatively standard and 

discussing the merits of each . A more general account of benthic sampling can be found 

in Holme and MacIntyre (1984) . A manager charged with getting information pertinent 

to the regulation of any marine habitat is faced with competing choices in the adoption of 

sampling methods and designs. First, there is need for standardization in order to make 

data collected through time, at different places, and by different investigators truly 

comparable. Second there is the need for innovation when it is known or strongly 

suspected that standard methods are inadequate . As a general statement, it is easier to 

adopt standard methods in shallow water than in deep. This is because far more 

equipment development, use, and maturation has taken place shallow. In contrast, deepsea studies are still relatively innovative in terms of equipment and design . 

2.7 .2 Sampling Design 

The most common and damaging series of errors in ocean impact studies has been 

the failure to concisely define the question being asked, the failure of adopting a 

61 
sampling design which allows the question to be answered, and the failure to analyze the 

data in a way that produces unambiguous statements (Carney 1987). In part, these errors 

have stemmed from a preoccupation with the logistical problems of working at sea, such 

that "design" comes to mean cruise schedules and gear deployment rather than an orderly 

collecting of data suitable to the testing of prior hypotheses . Given the special logistical 

problems of the deep sea, these errors will be very easy to repeat . Therefore, this 

discussion of methodology begins with a consideration of design . 

Developing Trends In Data Analysis 

Since deep-sea resource management is a relatively new field, program planners 

are somewhat more free to take advantage of new ways of conducting studies. It is 

important that trends in data analysis be recognized . Data analysis in oceanography and 

ecology has undergone a dramatic change in the past ten years. As studies of the deep 

environment are undertaken, these changes afford both new opportunities and new 

challenges . The most easily implemented opportunities are associated with the relative 

ease with which the massive data typical of ocean monitoring can been manipulated and 

subjected to simple visual inspection. There are few uncertainties associated with this 

technology. Much more complex is the changing conceptual issue of how data are used 

and the link between analytical result and conclusions . 

2 .7 .3 Increased Data Access and Ease of Visualization 

We are presently experiencing a revolution in the manner in which data can be 

accessed and examined which should profoundly effect all environmental studies that 

produce large volumes of data . In the past, the difficulty of managing data forced 

managers to depend upon statistical abstractions such as means, variances, diversity 

indices, etc. to arrive at conclusions about patterns in data. Presently, it is now possible 

for anyone with a fast and memory-loaded personal computer or a relatively modest 

workstation to easily accesses many gigabytes of data from a standard archive, such as 

those being developed by the National Oceanographic Data Center (NODC). These data 

can then be examined "by eye" using visualization techniques ranging from simple 

plotting to image-based data representation . 

There are two very important management consequences of this ready access to 

data. 

Better Sequencing of Study Tasks - Traditionally, fiscal restraints and the long 

lead time between data collection and final analysis forced managers to 

combine tasks which should logically be completed step by step . Rather 

than determine the physical aspects of an environment first, and then 

undertake an appropriately partitioned sampling of fauna, physical and biotic 

aspects would be determined simultaneously using designs that were poorly 

suited to either task alone. Fiscal restrictions are now the only cause for such 

ineffective studies. The collection-analysis gap has been so greatly shortened 

that it is possible to do complete analysis of preliminary physical surveys in a 

shorter period of time and then undertake optimally designed ecological 

work. 

62 
Decreased Emphasis upon Summary Statistics - Now that it is possible to 

calculate every known diversity index for a given data set in a matter of 

seconds, management need to depend upon a standard value such as H' is 

greatly decreased. This advancement places a much greater burden on the 

quality and timeliness of original data. As computer developments have 

brought the end user closer to the massive raw data, the quality of that data 

must be improved. Summary statistics often hide poor data quality which are 

glaring during simple eye examination. Therefore, management must 

stipulate that data be submitted in a clean and usable form early in a project, 

rather than as the final act. 

2.7 .4 Changing Approaches to Statistical Analysis 

Ecologists have a long tradition of being dissatisfied with statistics. In some 

instances such dissatisfaction has been intended to mask insufficient understanding of 

techniques and sloppy design. However, beyond the masking of inadequacies, there has 

been a real and very legitimate feeling that traditional statistics are too demanding upon 

design and not especially informative if all demands have been tediously met. Often it 

seems that only trivial hypotheses can be correctly tested. Especially in applied ecology, 

we encounter the greatest interest in development of more informative statistical 

methods. As a result, every decade there is a resurgence in Bayesian methods, and such a 

resurgence is now underway. 

Most oceanographers or ecologists taking a graduate course series in statistics 

might have encountered the term "Bayesian statistics" but gained no other insight of this 

approach. Typically, we are instructed in traditional statistics derived from a synthesis of 

the concepts of hypothesis testing and estimation developed by Fisher, Neuman and 

Pearson. This highly standardized approach is sometimes called sampling-theory 

statistics, frequentist statistics, etc. Bayesian statistics takes a different view of 

hypotheses which specific causality. Rather than testing them per se, Bayesian methods 

seek to improve upon prior knowledge about the probability that an event has occurred 

and been caused by one particular factor out of two or more possibilities. The 

applicability of Bayesian methods in ecology has been discussed for at least thirty years 

but is now enjoying a resurgence of interest due to the linking of statistics and decision 

making. Bayesian-oriented centers, such as the Duke University Institute for Statistics 

and Decision Theory, are emerging and actively pursuing ecological application. 

The most often cited basic reference to Bayesian methods is Box and Tioa (1973) . 

A non-dogmatic text is that of Press (1989), and new texts focusing on applied ecology 

will surely appear soon. The origin of Bayesian statistics are attributed to the theorem 

concerning conditional probabilities of an event being due to one of many possible causes 

developed by the English cleric Thomas Bayes in the 1700's . The Bayesian central idea is 

that prior information often exists and should be expressed as an informative prior 

probability distribution . The primary task of sampling and analysis thus becomes 

gathering data to revise this prior information and arriving at a posterior distribution . 

Bayesian statistics are conceptually appealing since they appear to deal with the 

needs and information level of ecological managers. Rather than rigidly test alternative 

hypotheses, Bayesian methods seek to improve our understanding of the likelihood of a 

63 
hypothesis, and they employ prior knowledge. Unfortunately, while the application of 

Bayesian methods to applied ecology is increasingly advocated (Anderson 1998), 

managers must keep in mind that the overall validity of some Bayesian concepts is not 

agreed upon (Moore 1997). 

2 .7 .5 Times Series and Intervention Analysis 

While the term "baseline" is still useful for describing initial conditions in an 

environment, we now know that environments are not static, and the "baseline" data 

collected at a particular point in time are unlikely to have much long-term value. 

Certainly, deep-sea population data collected in the 1980's are not the best data to use as 

the before case in drilling associated impact in the year 2000. These older baselines are 

still valuable, however, in letting us anticipate the fauna present, anticipate the need to 

partition sampling in a non-homogenous region, and estimate the degree of replication 

needed for certain levels of statistical power. 

Ideals of appropriate "before and after" data have been evolving (Stewart-Oaten 

1996a) and now can be viewed in the context of time-series analysis, especially the topic 

of Intervention Analysis. Intervention Analysis is a development in time-series analysis 

attributable to the same two statisticians who popularized the Bayesian approach, Box 

and Tiao; in this instance the basic reference is Box and Taio (1975). It is 

understandable, that the advocates of Bayesian methods and of Intervention Analysis are 

often the same people. The approach is very attractive to management because it focuses 

upon a factor that is very often known, the moment in time that a potentially disturbing 

event starts. Underlying the approach is a hypothesis about when a change in time series 

data is expected. The hypothesis may be simple or complex in terms of what type of 

response takes place. The task of the analysis is to determine from data prior to the 

impact the normal patterns present and then predict the conditions which should be 

present at the onset of impact (intervention) . Impact is assessed as departures from the 

expected behavior. 

Among the major problems of time-series analysis is the need to understand the 

underlying model (Stewart-Oaten 1996b). Obviously, in the deep sea many different 

factors may be controlling benthic populations, and these factors may come and go in 

various combinations through time. Therefore a simple time-series model, while it might 

fit past data well, will be of limited predictive capability . 

2.7 .6 The Role of Replication 

There has been a tendency in ocean monitoring to be too rigid about replication 

when specifying performance requirements ( e.g. there should 3 or 5 replicates), matched 

by a casual disregard for the purposes of replication in the final data analysis (analyses 

are often based upon pooled replicates). In undertaking deepwater studies these two 

errors need to be avoided. The level of replication should be appropriate to the question 

at hand. It is common for statisticians to see replication as serving one primary purpose. 

However, in species-level ecology it often serves two. In the statistical context it allows 

for the estimation of inherent variation within a site so that statements about variation 

among many sites can be made with a known level of confidence. In sampling theory 

replicates are the sole source of information about variation, and under certain conditions 

64 
of homogeneity variance decreases as replication increases . Therefore, extensive 

replication is seen as desirable if not necessary, and replicates are never pooled. In 

Bayesian statistics prior information is used to determine prior distributions which are an 

initial model of variation. In such an approach, replicates are not the sole source of 

information ,and the need for extensive replication may be relaxed. In the biodiversity 

sense (species inventory), replicates produce the cumulative list of species within a site . 

The deep sea is always under sampled and there are many rare species. Therefore 

extensive replication is considered necessary, and replicates are always pooled when 

estimating species richness. Letting the degree of replication be driven by the need to 

maximize the estimate of species diversity is very difficult in deepwater where diversity 

can be very high. Jumars (1981) has discussed this problem in conjunction with nodule 

mining in the mid Pacific . The problem is basically this: the deep sea is diverse and has 

many rare species which may be represented by a single specimen in a sample of 

thousands of individuals . Presumably, there are many other rare species which have gone 

uncollected . If, replication is extended until some high portion of these very rare forms 

have been collected, they will be so rare in the data that they can not serve as a basis for 

statistical comparison. Therefore, the great effort and cost of considerable replication 

contributes little of practical use. 

Deep-sea studies should be undertaken with the primary purpose of replication 

being statistical in the sampling theory sense, and pooling only done analytically, not 

physically. The degree of replication will depend upon the purpose of the study and the 

variances found in preliminary data, Baseline studies should take a mapping form. 

Since the deep-sea is poorly known and many sampling programs carried out back when 

the environment was assumed to be homogenous on the scale of kilometers, it can be 

argued that a mapping of fauna on finer scales is needed. For example, rather than 

restrict samples to a narrow transect of stations, scatter numerous samples across a swath 

of ocean bottom. Replication at each station would be traded for greater spatial coverage. 

Specific impact studies should continue in the tradition of within site replication . 

However, by placing fewer sites wisely and carrying out only adequate pre-impact time 

series, overall effort can still be kept to reasonable limits . 

2.7 .7 Ships, Submersibles, and Other Sampling Platforms 

Access to the deep ocean environment has traditionally been by means of ship and 

submersible. While these will play an important role in deep environmental studies, the 

ocean manager needs to consider the incorporation of advanced technologies . We find 

ourselves in a peculiar situation. The offshore oil and gas industry is exploiting deep 

resources through the development and application of pioneering technologies . However, 

as leasors these developers lack incentive to study the deep environment with the same 

level of sophistication. The primary burden of gaining knowledge of the environment 

resides in the "property manager", MMS, which has neither mandate nor funds necessary 

to undertake the necessary development. There would seem to be fertile grounds for 

cooperation. 

65 
Ships 

A comprehensive deep-sea bottom survey requires the use of a general-purpose 

oceanographic vessel . The principal vessel requirements for deep-water surveys are 

related to the need for long lengths of cable and over-the-side gear handling capability . 

Trawling and use of a large box core require a wire rope at least 0.5 inches in diameter 

and at least twice the depth to be sampled. For example, in the Gulf of Mexico about 

8,000 m of line is needed. Adequate winches with more than 10,000 m of suitable line 

are found on University National Oceanographic Laboratory (UNOLS) vessels in the 180' 

class and larger. The A or U frame of the vessel must be large enough to accommodate 

the box core frame. In addition, a conducting hydrowire slightly greater than maximum 

bottom depth is needed for CTD sampling of the water column. 

Submersibles 

Submersibles are specialized sampling platforms that have carried out a wide 

range of basic science sampling missions in the deep-sea. However, there use in applied 

deep-sea ecology has been much more limited to work on unique habitats such as seep 

communities and sampling around waste containers. The actual need for submersible in 

any particular study must be carefully weighed against the cost . It can be expected that 

the combined cost of a submersible with its support ship will be triple the cost of a 

similar size research vessel alone. The operators of the two readily available 

submersibles, Johnson Sea-Link and Alvin, do try to offer full oceanographic capabilities 

on their support vessels. In practice, however, deck space and gear limitations combine 

with inexperience and time conflicts to make submersible support ships of limited utility 

in general deep sampling. This reality requires that either a survey be almost entirely 

submersible based or employ two vessels at great expense . 

Deep submersibles are the sampling platform of preference when three conditions 

prevail. 

1 . When a high degree of spatial control in sampling is needed. 

2. When samples must be taken with the absolute minimum of disturbance. 

3 . When deployments of experiments or monitoring devices require precise 

control and at-the-site operator discretion . 

However, these advantages are obtained at a great dollar cost and a great reduction in 

sample yield when compared to ship deployed equipment. Therefore, from a 

management perspective, submersible operations must be justified on a relative cost of 

information basis. In many cases submersible sampling may be more appropriate for 

basic research into deep ecosystem function than for routine monitoring. In the following 

sections, the types of data that submersibles are ideally suited to gather will be briefly 

outlined and discussed from a management perspective. 

Submersibles are virtually mandatory in the study of deep special environments. 

When the region of seafloor under management is known to contain special habitats, such 

as chemosynthetic communities, then manned submersibles are the sampling platform of 

choice . These habitats are very spatially homogenous, and sample site location requires 

on-the-site discretion . Use of submersibles for deep soft bottom sampling is probably 

66 
justified in a research, rather than survey context. A central theme in current thinking 

about deep-sea diversity if that geological and biogenic structure of the bottom is 

extremely important as agents of habitat heterogeneity. If this is true, then the 

knowledgeable placement of samples in the bottom becomes critical . A core taken next 

to a burrow may not be biologically equal to one taken far from a burrow. Similarly, but 

on a somewhat larger scale, a core taken on the up current send of a low relief rise may 

not be equal to one taken on the down current side. To some degree, simply adding video 

or photography to a corer can provide this information, but in a very low efficiency 

manner. From a submersible, an investigator can seek out the particular bottom fabric of 

interest and execute a highly efficient sampling program. 

Submersibles have a host of limitations; the first is availability . In the US only 

two submersibles capable of high spatial control sampling are routinely available to the 

oceanographic community. These are the DSV ALVIN and the Johnson Sea-Link. The 

ALVIN is housed at Woods Hole Oceanographic Institutions and operated by the 

National Science Foundation (NSF), the Office of Naval Research (ONR), and the 

National Oceanic and Atmospheric Administration (NOAA) under a three party 

agreement. Research projects supported by these agencies receive prepaid dive time and 

are given priority in long-term scheduling. It is not unusual to wait three years to get on 

the ALVIN schedule once a project is completed . The Johnson Sea-Link is operated by 

the Harbor Branch Oceanographic Institution (HBOI). Initially the sole focus of HBOI 

oceanographic activity, the submersible is now managed as an operational capability add 

on to the HBOI vessels in the University National Oceanographic Lab System (UNOLS). 

HBOI maintains two Sea-Link submersibles, but only one is presently operated. 

Remotely Operated Vehicles and Autonomous Vehicles 

Deep submersibles are an available, time-tested technology of known limitation . 

However, they are expensive and suffer from limitations. As industrial activity increases 

in deep water, it can be assumed that better means of working at depth will become 

available. Remotely operated vehicles (ROV) and autonomous vehicles (AV) will be 

able to meet the same sampling needs as submersibles . A manager's primary concerns 

about both these systems should revolve around cost and reliability . 

Sampling Devices and Sample Processing 

Macrofauna, meiofauna, interstitial water, sediment components, contaminants, 

and tracers are all sampled simultaneously by a coring device . Due to the very high data 

yield of this activity, it requires highest priority in planning and execution. Megafauna is 

sampled by trawling, and image-based systems provide a survey of some megafauna 

along with some appreciation of bottom conditions. Comprehensive surveys need to 

employ these techniques well, but the lower data yield suggests a reduced allocation of 

resources. 

Changing Deep-Access Technologies 

Table 2.7 presents a summary of five technologies based on cables . When large 

cores and trawls are needed, there is still no replacement for a wire rope of at least 0.5 

67 
inches diameter on a heavy duty winch. Pingers and clever design of the on-bottom 

device can greatly reduce uncertainties about sampler performance, but data telemetry via 

the cable is not possible . Conducting cables are now routine on all oceanographic ships, 

but with few exceptions are limited to smaller diameters and lower load application. The 

most common application is in CTD casts . Since the conducting coaxials are quite 

sensitive to strain these cables are ill suited for heavy loads. The bandwidth of these 

coaxial cables is limited. 

The newest application of conducting cable technology is in the area of fixed 

bottom stations . The telecommunications industry is replacing its conducting cable 

submarine networks with fiber optical systems. The latter can transmit much greater data 

rates, are immune to electrical ground fluctuations, are immune to electromagnetic fluxes, 

are more resistant to corrosion, and much more resistant to ease dropping. There have 

been discussions between the telecommunications industry and the oceanographic 

community for approximately 10 years as to how abandoned lines might be used in 

research . Hilo-I was brought on line in 1998 as a deep seafloor seismic station operated 

by Scripps Institution of Oceanography, and future development of that system can 

include biological experimentation. Use of seafloor cables in applied studies will be 

limited by the distribution of such lines . There are none in the northern Gulf of Mexico. 

Fiber optic cable has an extremely wide bandwidth for data transmission . Fiber 

optic tethers to deployed gear have been employed in oceanography to a limited degree 

since the 1980s. However, the special cables capable of large weight loads and compact 

coiled storage are extremely expensive and still developmental. Permanent deployment of 

communication lines to fixed ocean stations is now being developed at Rutgers 

University and Woods Hole Oceanographic as part of the LEO-15 program. Currently, 

this is a nearshore program only 9 kilometers off New Jersey, but the concept can be 

extended to deep water. This seems to be a technology well suited to fixed-site 

monitoring in other deep areas such as the Gulf of Mexico, where extensive fiber-optic 

communication system development is anticipated. Support of fixed stations could be 

from vessels or fixed facilities . Vessels include ships, submarines, drilling platforms, 

storage spars, floating production facilities, and any other ship-like platform capable of 

deploying and recovering instruments and samplers. Fixed facilities include shore-based 

terminals, immobile seafloor structures, fixed buoys and other platforms which may 

connect to a transmission cable but do not deploy, recover, and redeploy instruments and 

samplers in a traditional mode: 

Box Cores 

Box Cores 

As with all of deep research, coring methods continually evolve, and managers 

need to weigh the benefits of new methods against the comparability of data. The desired 

sampling goal is to recover a section of the seafloor retaining all epifauna and infauna 

while preserving the geological structure and chemical gradients . Such an ideal sampler 

would work identically at all depths and on all soft substrates . For approximately 25 

years, the 0.25 m2 U.S . Naval Electronics Lab (USNEL) boxcorer (Hessler and Jumars 

1974) has been the most widely used sampling device for deep studies conducted in the 

US and Europe (Gage and Tyler 1991). Now there is a shift in interest away from box 

68 
samplers that yield a single large volume of sediment to multi-core devices that produce 

multiple small samples. 

The USNEL boxcorer has a frame mounted, 0.25 m2 spade closed box. The frame 

is lowered to bottom on a heavy cable, where weight and cable tension insert the box and 

close the spade. The frame assures a constant angle and rate of sediment penetration, 

independent of wire angle and descent rate . It was recognized by biologists and 

geochemists that the bow-wave of the device caused some disturbance of the sediment 

water interface. To minimize that bias and examine within-core spatial patterns, the box 

was partitioned five-by-five and only the inner nine partitions used in faunal analysis 

(Jumars et a1 .1977) . The outer series of partitions could be used for chemical and 

geological analyses that were not dependent upon sampling the interface . This device 

and methodology have become the standard of reference for shipboard sampling of deep 

sediment and the associated chemistry, macro, and meiofauna . The fact that all these 

parameters could be determined from the same sample has been a strong feature of box 

core sampling. 

A desire to obtain better meiofaunal samples lead to development of new 

sampling devices in the 1980's . Traditionally, when boxcorers were used, subsamples for 

meiofauna analysis were taken on deck with small diameter push cores. Since large bow 

waves are not generated by such narrow tube, it seemed reasonable to replace the large 

frame-mounted box with a frame-mounted cluster of narrow core tubes. Named the 

Scottish Marine Biological Association (SMBA) multiple corer (Barnett et al . 1984). The 

device, gained wide endorsement by meiofauna biologists, and its superiority over 

subsampling of box corers definitively demonstrated (Bett et al . 1994). Although a better 

means of sampling meiofauna, the multicorer produces too small of sample volume to 

meet all the needs of macrofauna, chemical, and geological sampling. Thus, its adoption 

in large-scale surveys requires substantial additional sampling, and the all-from-one-box 

benefit of boxcore sampling is lost . 

Trawling 

While macrofaunal and meiofaunal ecologists have adopted a frame-mounted 

0 .25 m2 as a standard to employ and a system to improve upon, the selection of towed 

nets for megafaunal sampling remains largely subjective. However, an atlas of North 

Atlantic deep demersal fish was produced by Haedrich and Merrett (1988, 1992) using a 

Gulf of Mexico semiballoon otter trawl, making that net a standard of comparison . The 

maximum possible gape of the trawl is 14.7 m, but actual width while towing is 

unknown. The main net is 1 .5 inch stretch mesh, and the cod end is lined with 0.75 

stretch mesh. The Marinovich Brothers net company of Pascagoula Mississippi custom 

makes these nets for scientific use. Smaller and easier to deploy are beam trawls . The 

fixed geometry of the trawl mouth allows for an attempt at quantification, and the rigid 

beam provides a mounting point for cameras and other gear (Rice et a1 .1982) . Odometers 

can be added as part of the effort to quantify samples, but they tend to be unreliable 

(Carney and Carey 1980) . 

69 
Table 2.7 . Cable Technologies Suitable to Deep Ocean Environmental Studies. 

Technology Status and Era Applications Limitations 

Wire Rope Mature Technology Heavy load box imprecise sampling 

From Vessel 1880 - present coring, trawling, etc. location and 

geometry. 

Conducting Cable Mature Technology CTD casts, slow Limited weight 

From Vessel 1950's - present scan video & load, limited data 

telemeterin bandwidth 

Conducting Cable Trial Application 1998 Multiple instrument No sample returned, 

From Fixed Based on 

telemetering . limited access to 

abandonment of serviceable telecomFacility conductive telecom- munication cables . 

munication cables . 

Deep vehicle 

maintenance 

required. 

Fiber Optic Second generation CTD cast, video rate Very limited weight 

Tether development. scanning, multiple load, no electrical 

From Vessel 1980's - present instrument power transmission, 

telemetering very sensitive to 

damage during 

deployment and 

recovery. 

Fiber Optic Trial Application Very broad band No sample returned, 

Tether Proposed multiple instrument limited access to 

From Fixed Based on 

telemetering . serviceable telecomDevelopments in munication cables . 

Facility submarine telecom- Deep vehicle 

munications industry maintenance 

required 

Deep-sea trawling is not an especially sophisticated activity, but it is very easily 

done wrong if operators assume it is similar to shallow trawling . The basic physics were 

developed by Kullenberg (1951) during the Danish Deep-Sea Expedition aboard the 

Galathea. Large trawls are high drag devices of low mass which tend to "kite" as line is 

payed out. This causes line to go out horizontally much more than vertically, so much so 

that at shelf depths seven times the depth must be payed out to reach bottom. With that 

much wire out, for example 1400 m of wire in 200 m of water, the weight of the wire 

overcomes the combined drag of wire and net and carries the net to the bottom. In 

deepwater less scope is needed, not more. Below 1000 m twice depth is usually 

adequate. The reason for less scope is that the weight of 2000 m+ of wire rope is heavy 

enough to overcome the drag of the net. However, a common error is to pay out large 

amounts of line from a vessel moving at more than 1 or 2 kn . In such cases, the drag of 

the net is greatly increased and the weight of even a lot of wire can not sink the net. 

70 
Decreasing scope and going slower is the successful method. If an otter trawl is used and 

speed through water becomes too low, the trawl boards will cross and tangle . Assuring 

successful trawling requires use of beam trawls, which can not collapse, and acoustic 

pingers mounted on the trawl wire. Frequently the directionality of a ship's hydrophone 

is too narrow to receive the direct sound and ping from a pinger trailed behind the ship. 

In such cases a trailing hydrophone must be used. 

Image-Based Sampling 

The term Image-Based Sampling is applied to those methods which produce an 

image of the seafloor rather than return an actual sample of fauna and substrate . Today 

this includes still film photography, film tine, still digital images, and digital or analog 

video employing electronic storage media (i .e . magnetic tape, CDROM video, etc .) . 

Digital systems may depend upon either a matrix or line scanning device . Presently, 

there is very rapid development of high-level and consumer-level digital imaging that is 

already spilling over into deep-sea equipment development. Therefore, it is not prudent 

to make a flat statement as to the best system to be used. Rather, it is better to consider 

film photography the standard by which other methods may be judged. 

Image-Based Sampling is extremely appealing, but must be considered critically 

in designing studies. What is the purpose of the images to be obtained? Hecker's camera 

sledge work is noteworthy both in terms of relating animals to structure (Hecker 1982) 

and sampling in deep-sea canyons where coring is inapplicable and trawling impossible 

(Hecker 1990). Excellent quantification and aggregation analysis for dominant 

megafauna have been obtained from submersible (Grassle et a1 .1975) and cameras 

mounted to beam trawls (Wakefield and Genin 1987) . However, the literature presenting 

successful studies gives no hint of the vast majority of photo and video surveys that are 

never analyzed. Bulk-load survey cameras can take approximately 800 frames per 

deployment, while video takes 10,000's . Extracting useful final data from such massive 

raw data usually proves to be overwhelming. Imaging technology is appealing, but the 

actual benefits are not often evident. Unless specimens are required for other analysis, 

image-based sampling generally gives a better measure of items on the seafloor, but not 

those buried (Kidd and Huggett. 1981). 

When it is decided that image-based sampling is needed, a decision must be made 

among competing technologies . Film photography is a mature technology that achieved 

a very high level of sophistication in the early 1960's . As such, methods of deep-sea 

photography developed during that era (see Hersey 1967) are still applicable. Resolution 

is the primary criteria by which technologies are compared. 

Resolution is the ability to record fine spatial details. In film photography it is 

expressed as resolving power measured in lines per mm. In video it is expressed as scan 

lines per image frame, . and in digital imaging it is expressed as pixels per unit length or 

area. Very high resolution film can record about 200 lines per mm. This equates to about 

400 pixels/mm in digital terms. For a 35 mm by 25 mm photographic slide, that is 

14,000 by 10,000 pixels . If they are color pixels stored at 12 bits per primary color, that 

is 0 .63 gigabytes per image! Film is still an impressive medium. 

71 
In typical deep survey applications, resolution of video and digital systems is 

most often limited by the display system, then by the storage system, and least by the 

camera. There is little value in using cameras with a resolution more than twice that of 

the display device . The most common resolution in consumer electronics is that of 

computer monitors for MAC and Windows operating systems . These systems are 

designed to employ 72 pixels/inch. Even if the monitor is capable of higher resolution, 

the operating system use of better resolution is limited. There are an increasing number 

of color printers that print at very high resolution . However, with printers there is a 

complicating factor . In color monitors a dot equals a pixel. This is not always the case in 

printers, since most printers create color by clustering dots . Thus, a 1440 dpi (dots per 

inch) laser printer that dithers 2x2 produces a resolution of about 720 pixels/inch. Digital 

systems are still far behind film. 

Moored and Free Deployments 

Moorings are the traditional means of obtaining time-series physical data and can 

be used in that capacity in the deep sea. In studies of the deep benthos the vertical 

placement of meters should focus upon monitoring of the benthic boundary layer. 

Particle flux traps must be suspended within and above the boundary layer so that reflux 

can be partitioned from flux . 

At-Sea Cost Factors in Deep-Sea Studies 

J 

In spite of the host of new and potentially useful technologies, it can be assumed 

that deep-sea applied ecology will primarily employ traditional sample collecting from 

ships. Some of the costs can be relatively well anticipated and are summarized in table 

2 .8 . Equipment must either be purchased at full costs or leased, if available, at 10 to 20% 

of cost per cruise . A trawl is the least expensive equipment item, with a set of boards and 

a custom made net estimated at about $3000. Due to the low costs and likelihood of 

damage, trawls are not leased . Due to a lack of available 0.25 m2 box cores, existing 

ones must be leased or fabricated. The design is not protected by patent and could be 

duplicated by a qualified machine shop for a cost of approximately $15,000 per unit. 

Most oceanography programs have some corer sitting around rusting, but these should 

not be used in place of the standard device . Image systems using film can be purchased 

off the shelf for about $100,000. Digital systems usually have to have some degree of 

custom fabrication due to the rapidly advancing technology. Camera, lights, and data 

systems should be equal in costs to those of film photography or several times more 

expensive. Proprietary systems, such as laser line scanners, are protected by patent and 

must be leased or manufactured under license. Mooring costs will be determined by the 

equipment attached . Current, salinity, and temperature meters with the necessary 

pressure housing will cost approximately $25K per unit . Particle traps can be fabricated 

for about $2000 per unit . 

Processing costs are determined by the parameters measured. Megafauna 

sampling is low cost due to size and relatively low diversity. Full sample sorting is often 

completed at sea. Box core samples are labor intensive. Sorting the fauna from a single 

sample will take an experienced technician about one month. Chemical and geological 

parameters carry various per analysis costs but lack an extensive manpower loading. 

72 
Table 2.8 . At-Sea Cost Basis for Major Activities of Trawling, Box Coring, Bottom 

Surveying, and Moored Instruments. 

Activity Samples Produced Cost Scaling 

Trawl Megafuana for: Species Initial Equipment costs ($3k per 

Sampling Inventory, body trawl system) plus vessel time. 

analyses, and Low processing costs since 

tissue analyses . samples can be fully sorted at sea. 

Box Core Macrofauna for: Species Initial Equipment costs plus 

Sampling Inventory, body vessel time ($15K per corer 

analyses, and system) : 

tissue analyses . High processing costs of at least 1 

Meiofauna for: Species Inventory, month per .25 m2 sample for 

body analyses, and fauna. Processing low for abiotic 

tissue analyses . measurements, but variable on 

Sediments for: Grain and bulk exact parameter measurements. 

property 

description, and 

chemical analysis 

Survey Photo/ Megafuana for: LTR spatial Initial Equipment Costs ($ l 00K 

video patterns. & up) Field costs as with 

Bottom Images : textural trawling . Processing variable 

description. 

with method; about 10 

images/hour for photography to 

0.1 images/hour for advanced 

digital . 

Mooring Current profiles and time series . Initial Equipment Costs ($100K 

Deployments Particle flux per mooring). Concurrent 

Meters, Traps, deployment for synoptic data 

etc . Light and transmission requires multiple units with 

number set by number of 

moorings and depth strata . Field 

costs similar to box core case. 

Processing costs based on 

analysis of data and will be 

variable. 

73 
Image data are highly variable in cost. Photographs processed by an experienced 

worker can produce faunal data at about ten frames per hour. If the images are digital the 

processing time actually increases. The more computer manipulation, the greater the 

processing time. Moorings produce digital records and particle trap samples. Current, 

salinity, and other digital records can be processed in less than one man month per 

sampling interval . Particle trap samples can be processed at about the same cost rate as 

chemical measurements from box cores and will vary with parameters required . 

2.8 Conclusions and Recommendations 

2 .8 .1 Introduction 

At the beginning of this review a central question facing MMS was identified . Is 

there strong scientific evidence indicating that shallow-water management strategies are 

inappropriate for deepwater? After various topics have been considered, this single 

question can be rephrased as two related queries. 

1 . Is there strong evidence that the deep environment is so physically different 

than the shallow that impact concerns must also be different? 

2 . Is there strong evidence that the ecology of the deep fauna is such that impacts 

are more or less likely? 

It is the tenant of this conclusion that the answer to the physical question is yes. 

An answer to the ecological question is more tenuous, however, there does seem to be 

some valid concern that impact is more likely . In this concluding chapter the arguments 

for the answers will be reviewed and recommendations made. 

2.82 The Physical Deep Environment 

Conclusions as to the Unique Nature of the Physical Environment 

When deepwater is defined as starting at 200 m depth the environment 

demarcated by that line is both highly variable and different from the shelf environment. 

It is not, as assumed by some, a physically uniform system. 

Density, Salinity and Temperature - In avoiding impacts and planning studies, 

management should divide deepwater into two physical zones, a transition 

zone of rapid temperature change from 200 m to the bottom of the permanent 

thermocline (pycnocline) and a deeper zone of minimal temperature change. 

The demarcation will vary from place to place, but can easily determined from 

the literature and physical data archives for the region in question . In studying 

the upper zone designs must anticipate both seasonal fluctuations and short 

term transitions caused by mesoscale physical processes such as storm and 

eddy passage. 

2. ii hit - Sunlight is present in the upper physical zone, although near the 

threshold of human vision . The importance of residual sunlight and 

74 
bioluminescent signaling means that increase in turbidity may have negative 

impacts. 

3. Oxygen - While the oxygen minimum is usually thought of as having little 

ecological consequence, its presence requires special attention to discharges . 

Any material that has a biological oxygen debt may produce local hypoxia. 

4. Water Movement - Bottom currents in deep water are typically low energy, 

but episodes of high flow are sometimes encountered. A full understanding is 

needed to understand the biological environment and model plumes dispersing 

on or near bottom . 

Recommendations Based on Physical Results 

1 . Pressure - Fate and effect models used in shallow water should be reviewed. 

Employing reasonable physical chemistry models the effect of pressure upon 

critical reactions and solubility's should be considered . Based upon the 

results of this review, targeted physical chemistry investigations should test 

reactions for pressure effects. If significant effects are found, then new deep 

fate and effects models must be developed. 

2. Density, Salinity and Temperature - Due to the paucity of data, management 

is obligate to either develop the needed time-series data sets or work jointly 

with industry to make the necessary measurements. Due to its more dynamic 

nature, the upper physical zone should be sampled with greater temporal and 

spatial resolution. In general, sample density should increase towards bottom 

and not follow the oceanographic tradition of fewer samples near bottom . 

3 . Light - Light field measurement is needed for a full description of the deep 

environment. When turbidity is measured, large volume measurements (such 

as back scattering) may be more ecologically informative then beam 

transmission . 

4. Oxygen - The oxygen minimum will fluctuate with the water density 

structure. Oxygen can be measured concurrent to temperature and salinity . 

The biological oxygen debt at appropriate temperatures and pressure of any 

discharged material should be determined and evaluated in terms of producing 

local hypoxia. 

5. Water Movement - Traditional physical oceanography is best suited for 

studying the surface movement of the ocean. Management should avoid this 

orientation and require that the dynamics of the larger benthic boundary layer 

(BBL) and the dynamics of the sediment-water interface be the major focus of 

study. Deployments should most heavily sample the 100 m nearest bottom, 

with "at bottom" conditions being directly measured. 

2 .8 .3 Deep Biology 

Biological Conclusions 

As stated above, it is hard to provide definitive answers about deep-sea ecology 

and impacts . The few studies which set out to detect such impacts were either done 

75 
poorly or were terminated prematurely. Basic studies can only suggest possibilities . 

After some consideration it seems probable that deep ecology may be more sensitive to 

impacts. This point is developed in the following conclusions and recommendations. 

1 . Habitat - Deep ocean management can not accept the shallow-water strategy 

of recognizing special habitats on the basis of gross substrate differences (rock 

versus mud). The degree of habitat change which causes one area to be more 

important than another is not known for the deep environment. 

2. Natural History - Up until ten years ago generalities about deep-sea 

adaptations were seldom challenged . The slowly reproducing and slow 

growing animals envisioned would certainly be highly subject to alterations of 

their stable environment. Now it seems that the natural histories are as varied 

as the environment is variable . However, one pattern seems true and relevant. 

Detritus feeding is dominant and variation in food input is a major source of 

heterogeneity in time and space . Activities that alter such input and 

redistribution of food should be of primary concern. 

3 . Zonation - If the fauna in one part of the ocean differs from that in another, 

then possible impacts and management concerns might also be different. This 

is the fundamental issue, not where to draw lines and apply names. Deep-sea 

fauna does change with depth either gradually or rapidly on a species by 

species basis. Therefore, uniformity of impacts is unlikely. It is an easy 

undertaking to sample fauna at many places and quantify differences . Predefined zones are not especially useful. 

4. Diversity - The unexpected very high diversity of the deep sea remains one of 

the primary distinguishing factors separating the shallow form the deep. In a 

management context, this high diversity is difficult to deal with since it is 

unexplained. Current proposed explanations for deep high diversity suffer 

from the absence of comprehensive geographic data. However, diversity does 

not increase the stability of systems, it affords more species which might be 

impacted. 

5. Trophic Structure - In the shallow ocean productivity and consumption have a 

rapid feedback loop through the nutrient cycles . This is not true for deep 

animals. They must depend upon a supply of detritus which decreases with 

depth. Since food decreases exponentially with depth, abyssal populations 

will be more food stressed then upper slope. Therefore, activities which alter 

detritus influx may produce major impacts which worsen with depth. 

6. Bio e~nically Structured Environment - Central to some explanations of high 

diversity in the deep sea is the possibility that soft sediment biogenic 

structures (burrows, mounds, etc.) are vastly more important structuring 

elements than in shallow water. This suggests that activities altering such 

structuring may have major impacts . 

Biological Recommendations 

When considering physical aspects of the deep sea it was easy to give definitive 

recommendations since the results were straightforward. The uncertainty of the 

76 
biological conclusions calls for a different approach. Management needs to first test the 

conclusions borrowed from basic studies before applying them fully. The 

recommendations below attempt to provide such tests. 

Habitat - Management needs to test the hypothesis that all deep soft bottom 

habitats are similar within the overall changes imposed by faunal zonation. 

This test requires that the physical environment be known first and then 

sampling carried out with appropriate stratification across different physical 

regimes. A high level of spatial control would be needed for any such 

sampling. Box corers and imaging systems would be the major devices used 

once the physical environment had been described. 

2. Natural History - Since previously useful generalities are being challenged, 

management must discover the necessary facts. Reproduction studies are 

most immediately relevant since they bear upon the ability of a species 

population to recover from impact . Such studies could be initiated on the 

dominant species in each size class . 

3. Zonation - The pattern of species change with depth should be determined 

across any deep area subject to development. Samples should be evenly 

spaced with depth rather than placed according to a proposed scheme of 

zonation. Analyses should be limited to degree of species sharing after 

adjustment for different abundance's in samples. If high degree of faunal 

overlap is found, the a uniform management strategy may be used. If a high 

degree of faunal difference is found, then depth-specific strategies must be 

used. 

4. Diversity - Surveys should continue to be carried out at the species level. 

When possible industry activities should be incorporated into experimental 

studies which monitor diversity changes . 

5. Trophic Studies - The influx and utilization of organic detritus to the deep 

benthos should be included in future studies. The preponderance of deposit 

feeding and the low food levels indicate that this process may be easily 

impacted. 

7. Biological Structuring, - A means needs to be devised to effectively describe 

and quantify the extent of biogenic structuring of soft sediments. Such a 

"structuring parameter", would allow testing of the hypotheses that the deep 

bottom is habitat rich and allow monitoring of possible impacts. 

77 

3 Reanalysis and Synthesis of Gulf of Mexico Deep-Sea Benthic 

Studies 

3 .1 Introduction 

This review is based upon published reports and data archives provided by the 

original contractors and the National Oceanographic Data Center (NODC) . Material 

appearing in the original reports is repeated only to the extent needed. Early in the review 

it was found that the NODC files for the Northern Gulf of Mexico Continental Slope 

Study (NGMCS) were unusable. Dr. Benny Gallaway of LGL Ecological Associates, the 

original contractor, provided printed data files contained in the 3rd annual report of the 

project (Gallaway et a1 .1988) . The fact that macrofauna counts were provided at the 

replicate level in those reports made reevaluation feasible. The Pequegnat data do not yet 

exist in a computer archive form, and the main report Pequegnat 1983(x) does not 

provide full information. In order to compare the Gulf of Mexico with another wellstudied region, the NODC archive for the Atlantic Continental Slope and Rise study 

(ACSAR) was obtained. Since that archive did not reflect final sorting at the species 

level, the original contractor, Battelle Inc., provided an updated data archive. 

The studies of Willis Pequegnat and his students (the author being one) were 

largely exploratory investigations of a type no longer supported by funding agencies . 

They were a prolonged zoogeographic survey with great emphasis upon species-level 

taxonomy rather than processes and concepts such as diversity maintenance, trophic 

structure, etc. Such exploration really never has a definitive conclusion, but in 

Pequegnat's case it can be concluded that they were prematurely terminated due to shifts 

in funding. Pequegnat's studies were the initial invaluable observations upon which 

hypotheses were to be drawn and tested . In this content of hypothesis generation, 

Pequegnat (1983a) should be seen as a compilation of ideas rather than conclusions. 

Subsequently, the Northern Gulf of Mexico Continental Slope (NGMCS) study adopted 

many of Pequegnat's ideas as hypotheses to be tested . 

3 .1 .1 Data Sources for the Gulf and Comparison Studies 

The main publication of the Pequegnat studies is Pequegnat (1983a). Much of the 

work based on those samples appears only in theses and dissertations. The most 

comprehensive of these is Bright (1968), Firth (1971), James (1972), Kennedy (1976), 

Lipka (1975), Pequegnat (1970), and Roberts (1977) . The specimens from this study 

were extensively circulated in the international community of systematists, and it is 

assumed that there is a substantial systematic literature not easily linked to the Pequegnat 

studies. Since the deep sea was so poorly known when Willis Pequegnat of Texas A&M 

undertook his sampling in the 1960's every sample yielded important additions to 

understanding. Dr. Pequegnat died prior to the preparation of this report. His notes, 

samples, and other program related documents are archived at Texas A&M under the 

direction of Dr. Gilbert Rowe. Vouchers of most of his species are catalogued in the 

collection of the U.S .National Museum of Natural History. 

79 
The sampling results of Pequegnat are compiled into a single volume (Pequegnat 

1983a) . The NGMCS study produced a series of reports; most useful are the third and 

fourth year annual reports (Gallaway et al . 1988; Gallaway 1989) . An open literature 

publication (Pequegnat et al . 1990) provides a very brief summary of results. The 

appendix volume of the year III report is an exceptionally valuable document since it 

contains sample-level data for the macrofauna and megafauna samples. Dr. Gallaway 

was extremely helpful during the course of the review. Some specimens are still archived 

at LGL in Bryan, Texas. Fish samples are archived at Teax A&M. Voucher specimens 

were filed by taxonomic specialists at the U.S. National Museum of Natural History. 

Most of these vouchers have only been accessioned, the first step in the cataloguing 

process, and are less accessible than the Pequegnat material . 

The primary studies upon which to base comparisons of the Pequegnat and 

NGMCS results are the parallel studies supported on the US Atlantic coast by MMS. The 

most extensive summary of results are given by Maciolek et al . (1987) . 

A Caution About Data Archives 

Working with reconstructed data is always problematic because the archival 

source may introduce errors and be easily misinterpreted . In terms of all faunal 

components, the reconstructed data had 2157 taxon, and the NGMCS 2198 (Gallaway et 

al . 1988 Appendix A4). Greater differences were found between the reconstructed 

archives and summary statements (Gallaway et al . 1988) when subgroups were 

compared. The reconstructed macrofauna archives list 69,161 specimens in 1613 taxa 

from 326 samples. The final report of the NGMCS study cites 324 samples, but only 

about 50,000 specimens, and 1121 species. The reconstructed megafauna invertebrates 

contained 41,827 specimens in 544 taxa from 56 samples. The NGMCS study reports a 

similar "more than 40,600 invertebrates", but only 432 taxa. 

The method of reconstruction was as follows. Appendix C2 (Gallaway et al . 

1988) contains ten fauna count tables, two for each of five cruises (1 for polychaetes and 

1 for all other invertebrates) . The counts for each taxa in each replicate sample are given 

in 405 pages. Appendix C3 (61 pages) gives megafaunal in a similar manor, treating fish 

and invertebrates separately. Appendix C 1 lists meiofauna with replicates pooled. All 

data were read, reentered into a text file, and verified. As a check for errors, all unique 

taxonomic names and all unique stations were extracted. Obvious errors were corrected. 

The data were then structured as an ordered triple (name, sample, count) for additional 

analysis. 

The greatest source of difference between the reconstructed and original data may 

be due to the manner in which mixed taxonomic resolution was handled. The NGMCS 

study excluded nematodes and harpacticoid found in macrofauna samples. This review 

does not, accounting for some of the difference in specimen numbers. It is assumed that 

between the third year report and the final analysis an unspecified number of taxa not 

identified to species were dropped before analysis. This review retained all taxonomic 

categories. Additional errors may be due to hand reentry of hand-typed tables . As a 

result, faunal counts and species richness reported in this review can be expected to be 

higher than those of the original NGMCS study. 

80 
The NODC files for the ACSAR study contained less-than-species data and 

incorrectly formatted and positioned header records. Dr. Blake, one of the original 

investigators provided a more detailed file from the original contractor, Battelle . The 

Battelle archives employed a consistent, but non-standard, species code rather than the 

NODC code. Position and depth data were not recorded for each sample as per NODC 

requirements, but only for stations . Therefore, none of the scatter in location and depth 

associated with these surveys was preserved. Metadata, (information about the data) was 

not included, but could be gleaned from the various reports. 

3 .2 History of Major Gulf of Mexico Deep Ecological Studies 

3 .2 .1 Pequegnat Studies 

Between 1964 and 1973 Willis Pequegnat at Texas A&M undertook extensive 

sampling of the deep fauna in the Gulf of Mexico . Although occupying only nine years 

of his diverse professional life, this research produced a lasting association between the 

name Pequegnat and deep-sea ecology, especially in the Gulf of Mexico. In reviewing 

the utility of Pequegnat's work in the context of contemporary deep oil and gas 

development, it is important to understand the unique nature of those studies. Most 

importantly, the work was a long-term commitment strongly focused upon taxonomy and 

zoogeography of the larger organisms . While the study of deep-sea animals collected 

through extensive collecting does lead to ecological insight and conjecture, it does not 

meet the criteria of design and statistical strong inference that have been required in 

sampling programs for the last fifteen years. Due to Law of the Sea restrictions, vessel 

costs, and decline in the systematics' expert base, these contributions could not be 

repeated now. However, ecological conclusions beyond this outstanding species-level 

biology were acknowledged by Pequegnat to be highly conjectural and intended as a 

starting place for continued inquiry. 

The primary contributions from the Pequegnat deep trawling remain in seven 

doctoral dissertations that were not subsequently published in the peer reviewed 

literature . Some of this information was provided in the open literature in the form of 

taxonomic papers in Pequegnat and Chace (1970) and a folio series (Pequegnat et 

a1 .1971) . Fortunately, as deep-water oil and gas exploration became a more likely 

undertaking, the Gulf of Mexico Region Office of the Minerals Management Service 

(MMS) had the foresight in the early 1980's to support compilation and synthesis of this 

important information. 

Pequegnat Objectives and Design 

The Pequegnat studies spanned the entire Gulf (Figure 3 .1) over 9 years of 

sampling very much in the zoogeographic spirit of the European national programs of the 

1890's to 1950's. As such, its primary goal was discovery and it lacked the formalization 

of sampling according to a design specifically for the purpose of statistically testing a 

hypothesis. It was, the observation which comes before hypothesis. However, in 

providing a summary of this extensive work for management, four objectives were stated 

in retrospection . 

81 
1 . Describe and discuss the megafauna in the northern Gulf of Mexico. 

2. Provide photo-documentation of that environment. 

3. Identify Information gaps . 

4. Provide reasonable assessments of potential for impacts 

Pequegnat Methods 

The Pequegnat sampling program was evolutionary with respect to equipment. 

Samples were taken with six primary devices. Larger epifauna were originally collected 

with a Menzies dredge/trawl (Menzies 1964) . Due to the fine mesh and overall small size 

of this device, it was replaced after only seven samples by a much larger rigid dredge, the 

epibenthic skimmer. A three meter wide skimmer was used for 87 samples and a 2 m 

version for an additional seven. In the later years of the sampling, the skimmer was 

replaced by a 20 m head line otter trawl that produced larger samples but with an increase 

in specimen damaged. A total of 25 trawl samples were taken. 

The epibenthic skimmer is described in detail in Pequegnat and Chace (1970) . It 

was intended to sample large epifauna. It was a rigid welded frame with a gape of 3 .06 m 

x 0 .92 m covered on the sides with 1/2inch mesh and in the cod end with 1/4 inch mesh 

hardware cloth. Its rigid construction made it a rugged device which did not mangle 

specimens. Quantification was attempted using a odometer wheel device . However, as 

with similar systems (Carney and Carey 1980 ) this proved unreliable. 

When high species diversity was reported in the deep sea by Sanders et al .(1965 ), 

Pequegnat added to his equipment pool a macrofauna sampling device . Here again, 

sampling methods were evolutionary . A Campbell grab with a 0.62 m2 bite was used 14 

times between 1964 and 1966. It proved to be unreliable at depths below 200 m. A 

novel plow dredge was used 11 times in 1965 and 1966. It employed cultivator disks 

borrowed from farming equipment to turn sediment into a bag of 1/4 to 1 inch mesh. 

This device was subsequently replaced by a quantitative dredge, scoop dredge equivalent 

to Sanders' epibenthic sledge . It was intended to fill a 360 liter canvas bag with a lm 

wide slice of sediment sliced 5 or 10 cm deep. Depending on the cutting depth, a full bag 

would represent 0.36 m2 to 0.72 mz . Today, such small dredges have been replaced by 

box corers . Twenty nine samples were taken with this device . 

Two camera systems were used for bottom surveys. An Edgerton-design 35mm 

pressure-housed shutterless camera made by Alpine Geophysical Associates was initially 

used. It was replaced by a medium format (70 mm film) Shipek-design pressure housed 

camera made by Hydroproducts. An Edgerton-type shuttered camera is still available 

from Benthos Inc. of Falmouth Massachusets . The Shipek camera is no longer made. In 

typical application, the camera as triggered by a bottom contact switch . Bottom contact 

was controlled with some precision through use of a camera mounted pinger and a 

trigger-sweep oscilloscope connected to a hydrophone . 

Pequegnat General Findings 

Pequegnat's exploratory sampling gave rise to two major conclusions concerning 

the zoogeography of the deep Gulf. The most pronounced pattern was that of 

82 
83 

bathymetric species change, that Pequegnat chose to describe in the terms of zoogeographic 

zones. It should be noted that the study of species gradients of macrofauna rather than zones of 

megafuana did not become popular until the 1980's, a time by which Pequegnat had completed 

most of the Gulf sampling. 

200m

1000m 3200m

200m

1000m

3200m

90° W

25° N

0m

1000m

2000m

3000m

0 10 20

Pequegnat Station Locations

Sampling Intensity with Depth

All Equipment, n=184

Figure 3.1. Locations of Pequegnat Samples Across Gulf of Mexico and Depth 

Sampling Effort. 

In establishing zonal boundaries, Pequegnat employed a "polythetic" (many types of 

evidence) approach (Sneath and Sokal1973). He used geomorphology, the position of the 

permanent thermocline, the position of the oxygen minimum layer, the depth of the Straits of 

Yucatan sill, and the distribution of fauna. With the advent of computer methods and gradient 

analysis, it has become more usual to describe depth changes monothetically, using only faunal 

data. The polythetic approach of Pequegnat versus the monothetic approach of others is 

important to bear in mind when contrasting various proposed depth patterns. 

Pequegnat set the beginning of the deep sea by two criteria. The first was physical and 

consisted of the depth of the 18° C. isotherm. Typically found between 125 and 150 m this was 

the depth at which physical oceanographers thought seasonal variation became minimal (± 3° ). 

The second criteria was faunal and consisted of that depth at which the fauna had no estuarydependent species. On the basis of shrimp, this end of the shallow ocean could be set at about 

250 m. 
Table 3 .1 . Faunal Criteria for Establishment of Pequegnat Depth Zones. 

ZONE FAUNAL CRITERIA 

Shelf/Slope Abundant and species rich fish fauna, paucity of holothuroids, and 

Transition abundance of burrowing urchins 

150 - 450 m 

Archibenthal Horizon A - Fish still abundant, holothuroids increasing, 

475 - 950 m 

replacement of burrowing urchins by regular urchins, and 

replacement of shelf galatheid species by slope species. 

Horizon B - Fish still numerous but past the center of abundance, 

marked reduction of bracyuran crabs. 

Upper Abyssal Encounter fewer fish with deeper centered populations, 

975 - 2250 m 

holothuroids increasing, upper species fewer but still present. 

Mesoabyssal Horizon C - Marked reduction in species for all taxa. 

2275 - 3200 m Horizon D - Additional reduction of species with a few deeper 

species reaching their population maximum here . 

Lower Abyssal Reduced fauna, but distinctive species of holothuroids and fish . 

3225 - 3850 m 

Overlapping this upper boundary and extending to the maximum depth of the 

Gulf, Pequegnat envisioned five progressively wider major zones, the Shelf-Slope 

Transition (150-450 m), the Archibenthal (475-950), Upper Abyssal (975-2250 m), 

Mesoabyssal (2275-3200 m), and Lower Abyssal (3225-3850 m) . Within these zones, 

the Archibental is divided into two horizons, A (475-750 m) and B (775-950 m), and the 

Mesoabyssal divided into a Horizon C (2275-2700 m) and D (2725-3200 m). These 

subdivisions were not uniformly obvious in the entire Gulf of Mexico. 

A review of the faunal criteria used by Pequegnat for the recognition of these 

zones (Table 3 .1) shows that taxa were given very selective weights. Fish, holothuroids, 

urchins, bracyuran crabs, and galathaid crabs were the primary determinants . 

Recognizing the subjective choice of criteria, Pequegnat's zones can serve as a useful 

nomenclature. Overlying the basic pattern of depth zonation Pequegnat detected two 

larger-scale geographic divisions. Drawing a line somewhat arbitrarily at 90° W, the 

eastern region was considered a physically active (dominated by deep currents), and the 

western was tranquil. These physical differences were viewed as giving rise to habitat 

and faunal distinctions . There was no attempt to explain the differences in terms of 

84 
trophic relationships, since no studies of surface productivity or detritus influx were 

attempted. 

Beyond these major distribution patterns, Pequegnat offered some interesting 

speculation about trophic relationships. It was suspected that organic detritus influx 

through the water column might be insufficient to meet the demands of the benthic 

population . Dissolved organic carbon was dismissed as a possible food source, and large 

plant and animal falls considered minor factors . Food input via mass sediment transport 

was considered highly probable. The question can now be resolved through application 

of carbon influx studies and metabolic demand of the fauna . 

3.2 .2 NGMCS Study 

The Northern Gulf of Mexico Continental Slope study was carried out by LGL 

Ecological Research Associates Inc . of Bryan, Texas . The principle investigators 

included Dr. Pequegnat, then an emeritus professor of oceanography at Texas A&M. 

LGL had prior experience in benthic studies on the Gulf continental slope, and sought to 

add deepwater expertise through an advisory panel which included Dr. Robert Hessler of 

Scripps Institute of Oceanography (SIO), Dr. Fred Grassle of Woods Hole 

Oceanographic Institution(WHOI) (now Rutgers), Dr. Richard Rosenblatt of SIO, and Dr. 

Robert Ballard of WHOI (now the Jason Foundation). In the last year of the project Dr. 

Ballard was replaced by the author, Robert Carney then at Moss Landing Marine Lab 

(now Louisiana State University). 

NGMCS Objectives 

The NGMCS study in its approved form was quite ambitious and had a list of 

eleven objectives . 

" To determine the hydrographic structure of the'water column and bottom 

conditions at selected sites within the study area. 

" To determine and compare sedimentary characteristics at selected sites within the 

study area. 

" To determine the abundance, structure and distribution of animal communities in 

the deep-sea in the Gulf of Mexico 

" To relate differences in biological communities to hydrographic, sedimentary, and 

geographic variables .' 

" To assess seasonal changes in deep-sea biological communities in terms of 

abundance, structure, animal size, and reproductive state. 

" To measure present levels of hydrocarbon contamination in the deep-sea 

sediments and selected animals prior to, and in anticipation of, petroleum 

resource development beyond the shelf break. 

" To assemble together and synthesize appropriate published and unpublished data 

with the results of this study, summarizing on a seasonal and spatial basis all 

biological, habitat, and environmental observations and parameters. 

" To compare the biological and non-biological characteristics of the deep Gulf of 

Mexico with that of other temperate and subtropical deep-sea regions. 

" To assess the need for, and determine the type of studies to be conducted in future 

program efforts. 

85 
To conduct an effective quality assurance and quality control program which 

insures that all data acquired are accurate and repeatable within standards 

normally required for each type of observation, measurement, or 

determination. 

" To critically review, interpret, and analyze all observations and data acquired to 

redefine, as necessary, the research program in such a way as to avoid or 

minimize redundancy and to optimize the efficiency of all field, laboratory, 

and data management operations for future deep-sea studies sponsored by 

MMS in the Gulf of Mexico 

NGMCS Design 

Superficially, the NGMCS study looks much like a typical benthic survey with 3 

transects containing 5 stations each. If consistently sampled over a series, of cruises a 

factorial analysis of variance could be used to test the importance of differences among 

transects (geographic position), differences among depths (bathymetric position), and 

differences among times. In execution, the NGMCS study executed a very different 

design that sought to ask a series of independent questions with a changing strategy of 

sample placements. Sampling effort within the 3 by 5 design was varied cruise to cruise, 

and auxiliary samples were added as new questions arose. In order to understand the 

intention of the final design, it is useful to first consider the original proposal. 

Originally Proposed Design 

In 1983, well in advance of the current industrial interest in deepwater 

development, MMS issued Request for Proposal (RFP) 3046 calling for investigations of 

the Gulf of Mexico beyond the shelf edge. Ultimately, the winning proposal was that of 

LGL Ecological Associates of Bryan Texas. LGL pulled together a research team with 

elements from Texas A&M in a research capacity and consultants from WHOI and SIO. 

Willis Pequegnat served in a senior advisory capacity . 

As initially proposed by LGL, the study would not be the repeated sampling of 

fixed transects through time that typified previous shelf-depth studies supported by MMS 

in the Gulf of Mexico (Carney 1993). Rather, it would be a three phase effort beginning 

with two descriptive survey cruises followed by an "experimental survey", "natural 

experiments", and "short-term field experiments". Since these departures from traditional 

surveying would be developed from the initial descriptive efforts, they were not specified 

in advance. Somewhat prophetically (chemosynthetic communities were not discovered 

until 1984) it was anticipated that oil seeps might be studied in a "natural experiment" 

mode. 

When the somewhat vague proposal was modified to a more traditional transect 

sampling, a western, central, and eastern transect were selected to coincide with MMS 

planning regions. The five stations of each transect were centered in the middle of a 

Pequegnat bathymetric zone. The descriptive value of the stations sought to take 

advantage of previous studies and topographic features of interest . There would be a core 

of three transects, Eastern, Central, and Western. The Eastern would stretch from 27° 

40'N 85° 15'W to 27° 30'N 85.40'W across the Florida Escarpment in a region of 

moderate to strong bottom currents (scour obvious) and limited terrigenous input. The 

86 
Central would stretch from 28° 20'N 89° 40'W to 26° 40'N 89° 20'W near the 

Mississippi Trough in a region of high sediment and temgenous input. The Western 

transect would lie from 27° 25'N 93° 40'W to 25° 50'N 93° 30'W . and be a seaward 

extension of the well studied Flower Garden Banks area. This Western transect would 

cross a topographically complex region . 

In addition to the three core transects, five other possibilities were proposed but 

never sampled. Pequegnat (1983a) had viewed the Desoto Canyon as being both a 

distinct ecosystem and a zoogeographic boundary. Therefore, it would be sampled by 

two transects, one each on its eastern and western flanks . Oil seep effects and brine 

habitats would be studied by an additional western transect crossing both an active 

seeping area and the Orca Basin brine lake. As a final transect, two alternatives were 

proposed. There could be a westward-most transect forming a seaward extension of the 

South Texas Baseline Study or a southeastward most transect off the Southwest Florida 

coast. The western-most transect might also allow detection of IXTOC spill effects, 

while the Florida transect would be considered pristine. 

NGMCS Actual Design 

Whenever a sampling design is modified during execution of a project, some 

elements of the original design inevitably remain, sometimes at cross purposes with the 

final design . This effect can be seen in the NGMCS study. A conditional sampling 

mode, basing each subsequent step on each previous result was carried out. The great 

advantage of this approach is a high degree of flexibility that allows changes if the initial 

design proves pointless early in a study . Its great weakness, however, is that changes of 

purpose usually limit the strength of the conclusions that can be drawn during final 

analysis . In the NGMCS study, geographic and bathymetric range was improved, but the 

validity of hypothesis testing weakened by the changes that took place. 

The NGMCS study had to accommodate two major changes during its course. 

The most obvious change, discovery of chemosynthetic communities, was not the major 

cause of design problems, as might be thought . Rather, design modification to 

accommodate basic questions about deep-sea ecology not anticipated in the proposal 

were most detrimental. At the time the NGMCS study was proposed, the academic deepsea community was actively questioning the nature of faunal depth change, high species 

diversity, and detritus-based trophic structures. The ideas arising from this debate were 

collected in review papers that same year (Rowe 1983) and were not incorporated into the 

NGMCS design. As the project progressed, the scientific advisors saw this as a serious 

deficiency in the project, and major shifts in design were made in an effort to address the 

omissions. Most of the changes were made concerning the depth placement of samples 

and, the need to test the validity of the Pequegnat zonation schemes upon which the 

design was based . Unsuccessful pursuit of such a test drove sampling in the three final 

cruises at the cost of useful time series and consistency across transects. Cruise III was 

devoted to filling in depth gaps and completing a time series only at the Central Transect, 

while Cruises IV and V undertook sampling along isobaths at the Eastern and Western 

Transects . 

Failure to successfully test the zonation scheme was due primarily to a 

misunderstanding . This misunderstanding can be found throughout the documentation of 

87 
the NGMCS study where the debate about zones is incorrectly characterized as a matter 

of scale, Pequegnat's (1983a) fine scale versus Carney et al . (1983) coarse scale . While 

Carney et al .(1983) does suggest use of some simple terms for faunal zones that can be 

used when zone naming is convenient, the main point of that review was to call into 

question whether such zones were anymore than a subjective and technique-biased 

cutting of continuous gradients . Appropriate testing required higher sampling density 

across isobaths and sample placement independent of any prior zonation scheme. 

Sampling IflEe:r;Slty with Depffi 

Box Gems Only n=326 

151 . 

O ~ P 4 0 O 8 

O s ~ 

N

0 

s 

. .[' . ~~'1 O D 

i 

NGWICS St.atian Location.:p 

0 ?0 ?0 33' 

--------------------------------J 

Figure 3 .2 . Locations of the NGMCS Study Transects and Supplemental Stations 

with Depth Effort of Boxcoring. 

Regional Transects and Ancillary Stations 

The three main transects are shown in figure 2.2 . The Western Transect extended 

from near the Flower Gardens at 27° 25'N 93° 40'W to 25° 50'N 93° 30'W. This was 

viewed as a region of low currents and high topographic complexity. The Central 

Transect lay near the Mississippi Trough, beginning at 28° 20'N 89° 40'W and ending at 

26° 40'N 89° 20'W. It was seen as a region occasionally impacted by the Loop Current, 

typified by high sediment movement and minimal topographic variation. The Eastern 

Transect crosses the Florida escarpment, beginning at 27° 40'N 85° 15'W and ending at 

27° 30'N 85° 40'W. This region was seen as under the influence of strong currents and 

having limited terrigenous input. Since there was no replication of transects within each 

region, inter-transect differences could be confidently ascribed to the regional factors 

noted. 

88 
Consistent sampling of the fifteen primary stations (3 transects x 5 depths) was 

dropped after the second cruise . Ancillary stations were added for mixed purposes. On 

the third cruise, 11 stations (356, 492, 633, 881, 1017, 1191, 1428, 1465, 2100, 2518 and, 

2945m) were occupied on the Central transect to increase depth resolutions and sampling 

within isobaths increased. Rather than repeat this increased depth resolution on the other 

transects, cruise IV added 12 stations at the same depths as the primary stations 

effectively replicating within three depth zones (625, 850, and 2900m). Again changing 

design, on the fifth cruise, a series of 12 stations lying between the Western and Central 

Transect were added . These W-C stations started at 150 m and ended at 2250 m. In 

effect, they were a diagonal depth transect. In the end, none of the transects or depths 

had been sampled with sufficient consistency to allow for strong statistical testing of the 

intended three factors, transect, depth, and time. 

Primary Depth Series 

Prior to alteration of sample design, the NGMCS study sought to compare 

transects in the Eastern, Central and Western Planning regions. Sampling would span 

three years, 1983-85, allowing a minimal time-series study. Fiscal constraints limited 

sampling to only two seasons, spring and fall, for a minimal seasonal study. Pequegnat's 

(1983a) depth zones were used to partition the transects by depth. The depths of stations 

is shown in table 3 .2 . Pequegnat's Lower Abyssal Zone did not exist in the study area. 

Since there was no replication of stations within depth zones, inter-zone differences could 

not be confidently ascribed to scheme of zonation. 

Table 3 .2 . Main Depth Series Stations Based on Pequegnat Zones . 

Depth Series Pe ue nat Zone Station Depth 

1 Series Stations Shelf-Slope Transition Approx. 300 m 

150-450 m 

2 Series Stations Archibental Horizon A Approx. 600 m 

475-750 m 

3 Series Stations Archibental Horizon B Approx. 800 m 

775-950 m 

4 Series Stations Upper Abyssal Approx. 1250 m 

975-2250 m 

5 Series Stations Mesoabyssal Horizon C Approx. 2500 m 

2275-2700 m 

Time Series 

It is common for offshore surveys to encounter difficulties in maintaining a 

consistent time series of samples due to vessel and weather related problems. This 

problem is obvious in the NGMCS Study (Table 3.3). Only the Central Transect was 

repeatedly sampled on three occasions, fall 83 (Cruise I), fall 84 (Cruise II), and spring 

89 
84 (III). Subsequently in the final analysis only these fall 83 and 84 samples were 

compared to test inter-annual variation and the spring contrasted to the fall as seasonal 

variation. Both must be considered extremely weak tests which grossly under replicate 

season and years. 

The Eastern and Western Transects were sampled twice to a certain extent, but the 

objectives and station placement were different on the separate cruises. When initially 

sampled in the spring of 84 during Cruise II, the Eastern and Western Transects consisted 

of the same 5 Pequegnat depth zone stations used at the Central transect during Cruise I 

and Cruise II . However, following the second cruise, the program objective began to 

drift. Western and Eastern transects were not re-sampled until the spring of 85 (Cruise 

IV Eastern only) and one month later (Cruise V Western-Central only) . By that time, 

additional design-biased reexamination of the Pequegnat depth zones was no longer 

viewed as appropriate and along isobath sampling was preferred. 

Table 3 .3 . Timing of Sampling of Primary and Auxiliary Stations 

Western Central Eastern 

Primary Stations Cruise I Fall 83 

Cruise II Spring 84 Cruise II Spring 84 Cruise 11 Sprin g 84 

Cruise III Fall 84 

Cruise IV Spring 85 

Cruise V 

Ancillary Stations Cruise III Fall 84 

Cruise IV Spring 85 

Cruise V Spring 

85 

Cruise V 

NGMCS Methodology 

The basic field methods are presented here. Sample processing methods are 

discussed in conjunction with each if the faunal size groups . The NGMCS study 

employed a Neil-Brown Mark II CTD with a 12 bottle rosette sampler for water and a 

25 cm beam path Sea Tech transmissometer. A pair of yoked box corers were used. 

These were described as Gray-O'Hara modification J&O box corers with a 24.5 cm x 

24.5 cm bite in the NGMCS report (Gallaway 1989). Subsequently (Boland and Rowe 

1991) applied the name Gulf of Mexico (GOMEX) corer, giving the dimensions as 25 cm 

x 25 cm The core samples were partitioned by the use of cylindrical core tubes (Figure 

3.3). During Cruise I only six 3 .5 cm diameter tubes were fixed in the central portion of 

the box. On subsequent cruises the tubes were moved to an edge . Four of tubes were 

allocated to meiofauna analysis with a 63 ~tm sieve. The contents of the box cores, 

exclusive of the core tubes, was sieved at 300 [tm for macrofauna . After counting, 

biomass was estimated from counts using conversion factors in Faubel (1982) and Rowe 

90 
et al .(1974). Megafauna were collected with a 9-m semiballoon otter trawl equipped with 

60 cm doors and a 3 .8 cm stretch mesh net and 1 .3 cm mesh cod end liner. Photography 

was carried out with a Edgerton-design 35 mm camera drifted above bottom. 

General NGMCS Results 

The specific results of the NGMCS study will be considered in the following 

sections as the results of reexaminations are presented. As a very brief review, the 

primary conclusions were. 

" Macrofauna diversity is high but lower than in the Atlantic . This conclusion was 

not supported by reanalysis . 

" Macrofauna diversity lacks a deep maximum. This conclusion was supported by 

reanalysis. 

" Macrofauna biomass is lower than the Atlantic and is supportive of the Rowe and 

Menzel (1971) designation of the Gulf as an oligotrophic region . This 

conclusion was not supported by reanalysis . 

" Meiofauna biomass is very high. This conclusion could not be reanalyzed . 

" ANOVA at the species level reveal few differences transect to transect and even 

depth to depth. Reanalysis confirmed this conclusion . 

" The Pequegnat zonation scheme was considered valid . This conclusion was 

inconsistent with ANOVA results and to be subjective on reanalysis. 

" Unique systems exist in the form of chemosynthetic communities. This discovery 

can be considered the major contribution of the project. 

3 .2 .3 Atlantic Continental Slope and Rise : a Comparative Study. 

The primary studies upon which to base comparisons of the Pequegnat and 

NGMCS results are the parallel studies supported on the US Atlantic coast by MMS, 

ACSAR). The most extensive summary of results are given by Maciolek et al . (1987) . 

The Atlantic Studies considered for comparison consist of three separate efforts carried 

out by the same organizations and people . These consist of a Northern, Middle, and 

Southern cross coast series . The Northern and Southern were traditional descriptive 

surveys. The Middle Series were carried out in this same mode, but specifically 

anticipated deepwater development at a specific site on the 2000 m isobath. Therefore, 

the Middle series sampled bracketed a specific location. 

Inter-study comparisons are always problematic, and there are four primary 

differences between the NGMCS study and the Atlantic series which will cast doubt upon 

results. 

" Different Sampling Device - The Atlantic Studies employed a partitioned 0 .25 m2 

box core similar to the NELS Hessler design and devoted 0.09 in z of sample 

to macrofauna. The NGMCS Study used 0.06 m2 GOM cores with two 

replicates taken in tandem. From that, 0 .0569 m2 (Cruise I) and 0 .0475 mZ 

(Cruises II-IV) were devoted to macrofauna from each replicate. 

" Different Experience/Expertise - The Atlantic studies benefited from long history 

of macrofauna studies centered at Woods Hole, especially experience in 

sorting and identification. The primary deep experience in the NGMCS 

Study resided w/ Willis Pequegnat whose experience lay in megafuana. 

91 
" Different Depths of Sampling - The Atlantic design did not draw upon prior 

zonation schemes, and samples were generally collected at 500 m depth 

intervals (500, 1000, 1500, 2000, 2500, 3000, and 3500 m). The NGMCS 

study based sample placement upon a prior zonation scheme and sampled in 

the center of these zones (350, 600, 850, 1400, and 2500 m) . 

" Longer-term Context. The Atlantic studies have been well reported in the peer 

reviewed literature while the comparable data from the NGMCS Study 

results have not. As a result, the data base for the Atlantic studies has been 

progressively refined during the production of publications, while the 

NGMCS data base remained little used. 

C;ursel Subcora Garfigira=ion 

s :,ter-,.-i s 

'd 

CrLI I :Je.:r 11-V Box a-i1 C lJL7nffy`uC(1S Ills 

:ic ~rrcsrt 8 lhnul~cia 

St~ctix r. 

9.6 CIFi2 t lCb 

1+8aouly-jim S:urr:lr 

Area - 47.E ar[1 

--- } 

24.E an 

Figure 3 .3 . Box Corer and Arrangement of Subcores Employed in NGMCS 

Study. 

92 
3 .2 .4 Problems of Sampling Effort 

Patterns of diversity and distribution seen in samples from the deep sea are 

extremely subject to distortions imposed by sampling. Such distortions are especially 

prevalent when there are faunal gradients and sampling effort along those gradients is 

unequal . Sampling gaps and unevenness can produce false indications of boundaries . 

Therefore, it is important to review the actual bathymetric sampling effort . 

Neither Pequegnat or the NGMCS Study sampled equally along the depth 

gradient . Pequegnat's sampling (Figure 3 .1) was most concentrated above 1500 m. 

Below that, most depths (in 100 m intervals) were sampled once, twice, or not at all. The 

3 000 m to 3 100 m interval was sampled with the same intensity as the upper zones. 

Initially, the NGMCS study (Figure 3 .2) accepted a pattern of zonation proposed by 

Pequegnat and selected sample depth accordingly . During the course of that study an 

effort was made to modify the sampling design so that Pequegnat's zones could be tested . 

In spite of these changes, in the end sampling was focused above 1500 m with unequal 

sampling within zones, and the region between 1500 and 1800 m left un-sampled . 

Several artifacts can be expected from the decrease in sampling with depth and 

the gap in intensity between 1500-2000 m First, species richness below 1000 m will be 

underestimated relative to the upper region when depth patterns are observed. Second, 

faunal dissimilarity between the upper and lower slope will be exaggerated since more 

rare species will be collected in the upper region . Third, the homogeneity of fauna in the 

deeper region will be exaggerated. Fourth, gradients will appear to be split with one set of 

values above 1000 m and another below 2500 m. 

3.3 Physical Environment of Northern Gulf of Mexico 

The purpose of this chapter is to present a general picture of thermohaline density 

and dissolved oxygen in the Gulf I of Mexico. Both of these are important in division of 

the legally defined deep sea (200 m and deeper) into an upper zone which experiences 

fluctuations (200 to 1000 m) and a deeper more consistent zone. The Pequegnat studies 

included only cursory physical sampling, depending on the physical oceanography 

program at Texas A&M to provide a general oceanographic context. Consistent with 

MMS research stipulations, the NGMCS study included hydrocasts, but those data 

provide only a narrow time frame . Therefore, the profile database of the National 

Oceanographic Data Center was accessed using the trial data search system GOODBASE 

under development at Scripps Oceanographic Institution . 

When hydrocasts were taken by the Pequegnat program they employed the 

methods recommended by the Naval Hydrographic Office at that time. Water was 

collected in reversing nisken bottles set at fixed sampling intervals most appropriate for 

upper ocean studies. Temperature and depth were determined from protected and 

unprotected reversing thermometers. Salinity and oxygen were determined by 

appropriate wet chemistry titration. Consistent with the techniques of that time, the 

NGMCS took hydrocasts with a Neil-Brown Mark III CTD equipped with a twelve bottle 

rosette sampler and a twenty five centimeter beam Sea Tech transmissometer. Oxygen 

was measured by wet chemistry titration. The data reported in the GOODBASE searches 

are limited to bottle samples. 

93 
Thermohaline Density 

The density structure of the ocean is of fundamental importance in separating the 

deep sea from the shallower environment. The division into a low density upper and high 

density lower environment is due to solar heating and downward momentum transfer. As 

the result of these physical causes of the two layers, the deep environment contrasts with 

the upper in several important ways. Its is extremely low light, almost uniformly cold, 

almost uniformly of high salinity, relatively isolated from wind driven water movement, 

and dependent upon long-distance slow transport for oxygen. Many oceanographers 

would probably put the start of this deep zone, marked by isolation from the upper ocean, 

at about 1000 m. This is the approximate depth at which the permanent pycnocline (or 

the associated thermocline and halocline) become relatively constant . Since the legally 

defined deep sea begins at 200 m, it seems physically appropriate to treat the 200-1000 m 

range as a separate region . 

The important point arising from examination of the temperature and salinity 

plots of the Gulf of Mexico (Figures 2 .1 and 2.2) is that the depth of the permanent 

thermocline and halocline are quite variable through time . The "text book" notion that 

the permanent thermocline is a fixed feature is a product of limited sampling and too 

much simplification . It is now understood that mesoscale events such as eddies and 

storms cause temporary fluctuations of a few hundred meters . These displacements are 

of such a magnitude that the bottom at 500 m may experience a temperature change of 

more than 5°C . independent of seasonal heating and cooling. It is not known if such a 

shift has direct biological consequences, but it must alter the stability of gas hydrates and 

thereby place some role in the distribution of hydrate-based systems. 

A characteristic feature of the thermohaline profile of the Gulf of Mexico is the 

stability below 1600 m. The deep Gulf is filled through the straits of Yucatan . The sill 

depth effectively isolates the Gulf from the colder bottom waters of the Atlantic and 

Caribbean. This homogeneity may have major effects on water movement. In the open 

ocean water density usually decreases all the way to the deepest part of the bottom. This 

vertical stratification, although slight, is sufficient to oppose vertical transport of water, 

solutes, and momentum. Without such deep stratification in the Gulf, vertical transport is 

not opposed. One basic consequence is that the deep Gulf water is well mixed with an 

estimated residency time of only about 100 years (Chan and Welsh, per. comm.) . From 

the perspective of management, plumes and bottom water movement may be different in 

the Gulf than in more typical deep regions. 

Pequegnat (1983a) felt that the Gulf Loop and associated eddies must play some 

role in regional deep ecology, even though this physical system was poorly understood at 

that time. Accordingly, he proposed that a gradient of physical energy existed with a low 

energy "Tranquil" bottom in the west and a high energy "Active" bottom in the east. The 

primary cause was the presence of deep currents underlying the more easterly Gulf Loop. 

Oxygen 

Although the juncture of the upper ocean and lower ocean is usually marked by an 

oxygen minimum, more pronounced in the Pacific than the Atlantic (Figure 2.3), it is 

usually not considered a physiologically important feature. It should, however, be 

94 
important in a management context where discharges are an operational or accidental 

possibility. Any discharge released into the oxygen minimum might contribute to local 

hypoxia or anoxia . As a partial product of the physics that create the permanent 

thermocline, the oxygen minimum shows some of the same features as the thermohaline 

profile (Figure 3 .4). From the scatter of archived data it is seen that the Gulf has an 

oxygen minimum lying between 300 and 520 m. Below this minimum oxygen 

concentrations are high with some statistical suggestions of an east to west decrease. 

A detailed examination of oxygen in the top 1500 m shows indication of regional 

differences within the minimum zone. This can be seen in simple averages ignoring the 

structure of the curve (Figure 3 .4) and in polynomial fits to the scatter (Figure 3 .5). For 

averages, data above 100 m was compared with data between 100-600 m. The nearsurface values ranged from an average of 4.623 to 4.499 ml/L with no significant 

differences. The lowest values were in the west and may be due to warmer temperature. 

The averages within the minimum zone ranged from 3 .122 to 2 .604 ml/L with a 

consistent trend away from the SE quadrant. The use of a polynomial fit helped illustrate 

depth differences as well as confirm the concentration patterns seen in the averages. On 

average, the SE quadrant lying under the Gulf Loop has a deeper (508 m) minimum with 

a low concentration of 2 .970 ml/L. In the NE, where the Gulf Loop is only an 

intermittent feature, oxygen is slightly less well mixed downward resulting in a shallower 

minimum (417m) and a lower concentration (2.767 ml/L) . Possibly due to a slightly 

longer residence time, the water in the western Gulf has an almost identical depth of the 

minimum (405 m), but an even lower concentration (2.517 ml/L). 

3.4 General Observations About Fauna 

By far the most important result of previous studies of the deep Gulf of Mexico is 

the compilation of a faunal inventory and the slow gaining of natural history information 

at the species-level. This review has made no effort to add new information, and 

repeating of the excellent descriptions in Pequegnat (1983a) or the detailed sizefrequency data of NGMCS (Gallawayl989, Gallaway et a1 .1988) is beyond the projects' 

scope . As an introduction to that work, this section briefly reports the species-level 

information in the third annual report of NGMCS, then addresses through a reanalysis 

how many megafauna species there may be . This question arises from the observation 

that the NGMCS study produced different results than reported by Pequegnat. 

A list of Pequegnat megafauna ordered by abundance is given in appendix A. It 

was derived from tables in Pequegnat (1983a) . Appendix B gives a similar list of 

macrofauna found in the NGMCS study archives . Appendix C gives the macrofauna taxa 

lists of NGMCS. These lists are intended as a quick reference for persons designing 

species-level studies in the future . 

95 
Surface 4 .4 99 4. 62 3 

?- ~?-. ~i 

"+4 

HpqY,:~ 

" 1. 

D 

P - - - '~ 

H . =.w 

.ti . 

'°~ y 

~"r~t3'" 

f).? ci~ ; 

1 `?iy 

"YI1 . 

A~eY~+r 

. ~ .'p". 

'._C . . .cV. 

()'?70 Zone 

ib , _ 286 ~~j3 5 t.a Ls 

_ ._ ..~_. . . . . . . _ . . - -- 

. _ . . ._L_ . . . 

6 6 

Oxygen tnlA with Statistics at Surface (0-10m) and 

MInimum zone (300-5o0m) 

Figure 3 .4 . Upper Gulf Oxygen Values Obtained from NODC. 

96 
N1'. 

\ E ?.76i' 

/mi n - 417m 

D 

~\Ir 

-Mill : :: 

ZM1111-

11 :: :: 653-5 

2.970 

Z1111 n = 5-08111 

1 I=- 692, i 

E 

P 

T 

H 

Dissolved Oxygen m]A- Described by 

Polynomial (4th degree) Curves,0-1500m 

Figure 3 .5 . Upper Gulf Oxygen Polynomial Curves Based on Fourth Degree Fits 

3.4 .1 NGMCS Natural History Studies 

Gallaway et al .(1988) provides excellent information on the size frequency of 

trawled fauna and the stomach contents of selected fish . Eleven crustaceans and eight 

fish were analyzed for size frequency: the crabs Bathyplax typhla, Benthochascon 

97 
schmitti, Rochina crassa ; the shrimp Benthesicymys bartletti, Glyphocrangon aculeata, 

Nematocarcinus rotundus, Penaeopsis serrata, Plesionika holtuisi, Stereomastis sculpta; 

the squat lobsters Munida valida, Mundopsis robusta ; The fish Dibranchus atlanticus, 

Nezumia aequa, Bembrops gobiodies, Coelorinchus caribbaeus, Coelorinchus 

coelorhyncus, Poecilopsetta beani, Gadomus lomgifilis, Chaunax pictus, Chloroptalmus 

agassizi, Synaphobranchus oregoni, Uropphysis cirratus,and Peristedon grayae. It was 

concluded and confirmed in reanalysis that no age cohorts could be definitely identified . 

This was originally attributed to a lack a adequate sampling frequency. Examination of 

compiled size data, however, showed that most species had size truncation below 1 or 2 

cm in length . It seems more likely that that newly recruited sizes were not retained by 

the mesh of the trawls . A shift in sampling gear is needed to extend these studies. It was 

also concluded that a tight correlation between size and weight was evidence against 

variation between seasons, years, depths, etc . This conclusion should be viewed as 

tentative, since size at a given age is the appropriate parameter . 

3 .4 .2 Megafauna: How Well Known ? 

Since the Pequegnat samples were taken through out the entire Gulf of Mexico 

over an extended period, that species inventory for megafuana should be the most 

complete. If the NGMCS megafauna inventory is a subset of the Pequegnat inventory, 

then it can be concluded that the megafauna is relatively well known. A comparison of 

the two inventories suggest that many more species may remain to be discovered. 

The comparison was based upon simple matching of the species names in one 

study against the other. The reconstructed Pequegnat database contained 713 invertebrate 

megafauna taxa and the NGMCS database 544. Fish were excluded due to greater 

concern over sampling artifacts. Wherever possible changes in genus and species 

nomenclature were corrected for. When the taxonomic resolution of the studies differed, 

an informed decision was made as to whether there was an actual match. Generally, if a 

species-level identification and a genus-level identification had the same genus, similar 

ranges and somewhat similar abundance, they were considered a match. Identifications 

to species in both lists were considered valid. All in all, species-level identification 

predominated, and the subjective judgements had only a minor effect upon the results. 

3 .4 .3 Different Lists of Rare Species 

The matching of the two inventories is most informatively considered by rank of 

abundance. Since the NGMCS study was most consistent in reporting abundance, it was 

used as the primary study. The results are shown in table 3.4 . Abundance was split into 

five ranges on a somewhat logarithmic basis, species taken in NGMCS more than 1000 

times, 100-999 times, 10-99 times, 2 - 9 times, and once. Treating singletons separately 

placed special emphasis upon the rarest species . 

The megafauna inventories of the NGMCS study and Pequegnat overlap to some 

degree, but NGMCS is not simply a subset of the larger inventory. Of the 544 NGMCS 

taxa, only 208 were previously reported by Pequegnat. This suggests that the species 

richness for deep Gulf of Mexico megafauna invertebrates exceeds 1049 species, the sum 

of the species unique to Pequegnat (SOS species), plus the species unique to NGMCS 

(336 species), plus the species in common (208). The contention that the species 

98 
inventory is under sampled is reinforced by the abundance-level comparison . For very 

abundant (1000+ count) species the studies agree closely (89%). Even at abundance 

down to a count of 100, overlap is still pretty high (73%). However, when rarer species 

are considered (9 and fewer), the studies report very different inventories . 

Table 3 .4 . Taxa Overlap by Abundance Level in NGMCS and Pequegnat Studies. 

ABUNDANCE GROUP 

Specimen Count 

NGMCS TAXA ALSO IN Pequegnat 

1000+ 9 8 89% 

100-999 48 35 73% 

10-99 116 56 48% 

2-9 206 67 33% 

1 165 42 33% 

While it is easy to explain the low percent of inventory overlap for rarer species 

as arising from sampling differences, the limited overlap at mid-level (10-99) warrants 

more attention. It could be caused by a combination of five causes . 

" Temporal Variability - There were major changes in faunal composition. 

" Regional-Scale Zoogeography - While the most abundant animals are widespread 

through the whole Gulf, there may be regional subdominant taxa. 

" Local-Scale Zoogeography - The two studies may have unknowingly sampled 

different unique deep habitats. 

" Sample Gear Biases - Pequegnat employed a variety of gear, using the epibenthic 

skimmer the most. The NGMCS study made consistent use of an otter trawl . 

" Taxonomic Inconsistency - Identification of species spanned more than twenty 

years and utilized different experts. 

Long-term (decadal) trends in deep-sea faunal composition have not been studied 

in the western Atlantic or Gulf of Mexico, and changes in methodology would make any 

attempt to identify such changes from archival data highly dubious. However, major 

changes in megafauna dominance have been found using similar methods over a period 

of 10 years (Billet et al . in press) . The possible causes of a dramatic shift in holothuroid 

dominance are now under investigation . 

Unfortunately, large-scale zoogeography can not be examined with the data at 

hand. Pequegnat (1983a) does not report station-level quantitative data, and quantitative 

summaries do not include geographic data. Given the marked change in bottom 

geomorphology around the Gulf, some degree of regionalism is to be expected. 

Similarly, local-scale zoogeography is not easily addressed with the data. There are, 

however, suggestions that unique habitats were sampled. The NGMCS study seems to 

have encountered chemosynthetic and sponge-bank communities that Pequegnat did not. 

The high incidence of sponges (Polymastia (Radiella) sol, Thenea spp., and Desmacella 

sp .) in only the former study represents evidence of sponge banks . Pequegnat seems to 

have sampled more often in urchin aggregations that the NGMCS study missed . This is 

99 
evidenced by the unequal abundance of the epifaunal regular urchins Plesiodiadema 

antillarum and Phormasoma placenta, and the usually infaunal irregular urchin 

Brissopsis atlanticus . 

The third possible cause of inventory differences, sampling biases, is hard to 

evaluate without direct gear comparison. The two studies did produce very different 

ranks of abundance (Table 3.5). When the twenty most abundant species in each study 

are compared only four have roughly equal rank in both. Three of these are relatively 

mobile crustaceans, Penaeopsis serrata, Nematocarcinus rotundus, Stereomastis sculpta, 

and the fourth a relatively seditary ophiuroid, Ophiernus adspersus. If the gear used were 

grossly dissimilar in collecting bias, the agreement for these species would not be 

expected. As noted above, the mismatch for sponges and urchins suggests that 

differences reflect habitats sampled more than gear usage. 

Taxonomic inconsistency is a very difficult issue to address. While taxonomists 

go to great lengths to publish revisions as they are made, this is an arcane literature to the 

ecologist. Even more complex than application of the correct name, is changing 

expertise. Not only are different experts used, but the same expert has changes in opinion 

over many years of experience . In general, the megafauna of the NGMCS study should 

have been fairly consistently identified by the same experts or criteria used in the 

Pequegnat studies . This is especially the case for the crustaceans, molluscs, and some 

echinoderms. In other taxa there is certainly reason to expect taxonomic inconsistency. 

The ophiuroids are a prime example. During the Pequegnat studies the abundant 

ophiuroids were identified ad hoc by various people and never made the focused study of 

one expert . In the NGMCS study, Dr. Gordon Hendler of the Los Angeles County 

Museum examined voucher specimens. Pequegnat reported a dominant species 

Ophiomusium planum, but NGMCS did not report such a species at all among its many 

ophiuroids . 

Table 3 .5 . Rank Comparison of Dominant Megafauna in NGMCS and Pequegnat. Bold 

face indicates roughly similar ranks; ? indicates unresolved taxonomic 

confusion, and > indicates only a possible genus-level match. 

DOMINANT SPECIES RANK Pequegnat 

Study 

RANK in NGMCS Study 

Aeas . ? 1 

Desmacella s p. ? 15 

Plesiodiadema antillarum 1 67 

Brisso sis atlanticus 2 332 

Penaeo sis serrata 3 3 

Phormasoma placenta 4 139 

Para a rus s p. 5 >55 

Nematocarcinus rotundus 6 2 

Sytellaspsis pellucida ~ 7 ~ 122 

100 
Stereomastis scul to 8 12 

Gemmula eriscelida 9 349 

O hiomusium lanum 10 >91 

Benthod tes t ica 12 55 

GI hocran on nobilis 15 18 

O hiernus ads ersus 16 9 

Benthesic mus bartletti 17 39 

Pasi aea merriami 18 ? 

Mesothuria lactea 20 34 

Bath lex ha 21 4 

Gl hocran on aculeata 31 21 

Plesionika holthuisi 44 44 

Benthochascon schmitti 61 7 

Munida valida 63 6 

Pol mastia sol 124 13 

Uro thus nitidus 146 19 

O hiocamax asciculata 172 11 

Ch so or is a assizii 287 8 

Thenea s p. 290 14 

Trilasmis kaemferi 

inae uilaterale 

306 17 

Am hile is in of i >316 10 

3 .4 .4 Specific Taxa Considered 

The Enigmatic Holothuroid Peniagone 

In the photosurveys of the NGMCS study, the holothuroid genus Peniagone was 

the most abundant animal encountered. Oddly, no specimens at all were collected by 

trawling . In order to explain this dramatic difference in results, the literature on the 

genus and museum records were consulted. Peniagone (the name meaning spawn of 

poverty) is frequently dominant in trawl samples and photosurveys at the base of the 

continental slope (below 2500 m) in the Atlantic and Pacific. Pequegnat (1983a) did 

sample a few badly damaged specimens of this genus during his earlier sampling, and 

they were variously identified as P. islanticus, P. azorica, and Scotoanassa sp. (a closely 

related genus). 

101 
Peniagone is the most species rich genus in the deep-sea holothuroid order 

Elasipoda. Like other elasipods, it can be considered an indicator of deep-sea conditions. 

The Gulf of Mexico specimens are best identified as P. islandica on the basis of body 

morphology and spicules. However, species identification in this group is problematic, at 

best . Whatever the exact species, the Gulf Peniagone fits into the Vitrea Group . This 

group includes at least ten species from all over the ocean that are intermediate in 

morphology between animals that are known to be primarily pelagic (such as P. 

diaphana) or benthic (such as P. azorica) . Whether swimming near bottom with highly 

modified podia or crawling on bottom with more traditional tube feet 

Linked with the interesting range of foraging behaviors for this sediment feeding 

genus is the peculiar habit of forming dense aggregates, mounds of several hundred 

specimens per square meter (Menzies et a1 .1973) . Such extreme aggregation was not 

noted from NGMCS sampling, rather there appeared to be larger patches. Actual tests of 

aggregation were not presented, but at Central Transect station 4 aggregates persisting for 

a distance of over 200 m. Some Peniagone appear to be highly mobile and capable of 

finding and exploiting regions of high detritus influx . Such influx may reflect localized 

redeposition of material suspended by bottom currents. This adds to the suggestion that 

special topographic habitats may be common at mid depths in the northern Gulf of 

Mexico. 

3 .5 Zonation 

This reanalysis seeks to make a point about the management utility of zones and 

then determine the nature of change most appropriate to management. A substantial 

amount of discussion in the reports of the NGMCS study addresses the issue of the 

validity of the "zone concept" . Actually, delineating faunal zones is not a concept, it is a 

convenient means of summarizing complex distribution data. Its very real management 

value lies in that convenience, not an unproven list of causes . 

3 .5 .1 The Zonation Controversy 

The basic points are straight forward. Many deep benthic species do show 

distinct depth ranges, and it was popular during the early years of oceanography to define 

particular depth zones based on subjective use of scant biological data and better-known 

physical patterns. As more biological data were obtained and multivariate analysis 

became popular questions of the validity, homogeneity, and cause of apparent zones 

arose. Unfortunately, the added objectivity of the analyses was often outweighed by 

unrecognized biases, making some of the debate unproductive. 

In the 1970's the discussion about depth zones, which was largely unpublished, 

had centered on three different opinions. The most traditional view was that faunistically 

homogenous zones were present with sharp breaks (much like the tree line on mountains) 

associated with certain oceanographic conditions . Pequegnat held this view . A much 

more complex view was that homogenous and sharply delineated zones were the 

geographic manifestation of integrated ecological communities. Boundaries did not have 

to coincide with oceanographic features in this scheme. The third view, as represented by 

the review of Carney et al .(1983), was that homogenous zones and distinct boundaries 

may exist in places, but that subjectivity and analytical biases play too great a role in the 

102 
recognition of such zones. Many analyses, especially cluster analysis, break continuous 

gradients into artificial zones. Rather than constantly seeking refinement of sampling and 

analysis, the more productive course of research would be to study and understand 

distributions at the species level . 

The NGMCS study was designed to test the repeatability of Pequegnat's zones 

rather than the possibility that they were sampling artifacts. This criticism was voiced by 

the scientific advisor board of the project and efforts made to remedy the situation. 

Sampling density was increased on the central transect, but not in a zonation neutral 

manner. The sampling repeated the Pequegnat zonation scheme at a finer depth 

resolution. Then stations were added along isobaths. However, the finding of faunal 

homogeneity along isobaths was not a definitive proof of the validity of the zonation 

scheme. 

3.5 .2 NGMCS Analyses of Zones 

The NGMCS study examined faunal zones by a variety of methods: cluster 

analysis of similarity, coincidence of range limits, and by analyses of variance. All 

results were interpreted to be supportive of the Pequegnat zonation scheme. However, as 

stressed throughout this report, that conclusion was built into the design . In actuality, the 

only thing proven was that fauna was not homogeneous with depth. 

3.5 .3 Consideration of a Null Model for Restricted Depth Zones 

If fauna is distributed within homogenous zones that subdivide the continental 

slope, then species should show restricted depth ranges . A standard part of the education 

of ecologists is development of an appreciation for non-random patterns of distribution . 

Implicitly, we test all observed patterns against randomness, which is now often called a 

null model . Pineda (1993) is now exploring the null models of depth zonation. When his 

work is complete, there will be a much better basis by which to judge the natural of 

faunal change with dept. 

3.6 Geographic Differences Tested by NGMCS ANOVA 

The most extensive analysis of pattern undertaken in the NGMCS study was a 

series of four analyses of variance, ANOVA. Species-by-species, using 61 most 

abundant animals, 244 analyses (61 spp . X 4 ANOVA) were conducted. Together, these 

ANOVA tested 60 contrasts for a total of 3660 tests. (61spp . X 60 tests) . A careful 

consideration of these analyses is appropriate since they were the primary basis for five 

out of seven primary conclusions of the NGMCS study (see Section 11). 

l . There were significant east to west variations . 

2 . There were no significant inter year variations . 

3 . There were significant seasonal variations . 

4. There were significant depth variations . 

5. There were no significant differences within depth zones (note conflict with 1 

above) . 

103 
On reevaluation it was found that the inconsistency of sampling caused many of 

these tests to have uneven samples and a resulting low power. In this section these 

multiple tests are briefly reviewed. In reviewing and discussing the very extensive use of 

analyses of variance in the NGMCS study it is most informative to consider something of 

an ideal usage 

3 .6 .1 Consideration of an Ideal Case of ANOVA Use 

Analyses of Variance (ANOVA) have a special high standing as a means of 

designing studies, carrying out sampling, and testing hypothesis . While they may not be 

the best way in which to study the natural environment and are often misused in ecology. 

Green (1979) strongly endorsed their use for reasons amplified by Carney (1987) . The 

formality of ANOVA forces the user to be specific about intent and consistency in 

sampling. 

The failure to maintain a consistent sampling program through time resulted in an 

inability to carry out a simple balanced analysis using all samples to assess the apparent 

influence of transect (3 levels), depth (5 level), season(2 levels), year (3 levels), 

replication (3 to 6 levels) and the interaction terms. The four ANOVA actually carried 

out were piecemeal unbalanced comparisons. The approach used was that of examining 

all possible linear independent effects (orthogonal contrasts) . 

Transect studies of ocean fauna typically have hypotheses testing the apparent 

importance of three factors : transect location, depth along transect, and time. It is 

recognized that many factors may be at play in creating location , depth, and time effects. 

However, these are usually too poorly known to be used a priori to select sample sites 

suitable to specifically test them. When sampling is undertaken, a series of transect 

locations is selected, then stations marked at fixed depths . These stations are then 

sampled with some fixed level of replication at seasonal intervals to create a time series . 

This fixed station approach may not offer the statistical advantages of randomization 

within quadrats employed terrestrially. However, its logistic simplicity has made it a 

traditional offshore approach. 

The appropriate null hypotheses would be: 

Hi Faunal parameters are homogenous across transects at different locations. 

H2 Faunal parameters are homogenous across different depths. 

H3 Faunal parameters are homogenous across the time of sampling. 

H4 There are no interactions of transect, depth, and time (actually multiple 

hypotheses) . 

3.6 .2 ANOVA of Macrofauna in the NGMCS Study 

Macrofauna data were culled of nematodes, harpaticoids, and species-level groups 

with fewer than 90 specimens . This produced 60 taxa to which Vesicomya sp. was added 

as a sixty first due to an interest in the distribution of this apparent chemosynthetic form. 

Four main ANOVA were run separately for each species for a total of 244 main analyses . 

Within these main analyses a total of 60 contrasts were tested on each species for a total 

104 
of 3660 tests. Each test had an explicit null hypotheses. In effect, there were 

approximately ten times more hypotheses than there were grab samples. There may be 

nothing wrong with this extreme degree of "data fishing", and it could have lead to 

unexpected insight. However, in the case of the NGMCS Study it did not produce such 

insight, and the design used did not allow simple and powerful testing of the simple 

hypotheses about location, depth, and time. 

ANOVA # 1 Location and Time Differences 

Only the Central Transect had a time series of samples and was suitable for 

seeking seasonal or cruise effects. The primary regional hypothesis (Hl) was a null 

statement of no difference in faunal abundance between all three transects. Logically, 

this primary regional hypothesis gives rise to three pair-wise comparisons, W vs C, C vs 

E, and W vs E, but only one can be independent. The contrast of C and W was taken as 

the second regional hypothesis . 

The list of ANOVA # 1 hypotheses is quite complex (Table 3 .6). Within the five 

depth stations of each transect, the primary regional hypothesis can logically be divided 

into a series of depth and depth group versus depth and depth group comparisons. 

Regional differences were tested twice, seasonal differences once, and depth differences 

twenty times. Again, only four comparisons among the 5 depths meet the requirement of 

independence. These are the shallowest versus all the deeper in each transect (H2,H7, 

and H 12); the two shallowest versus the three deeper (H3,H8, and H 13) ; the second 

compared to the third (H4,H9, and H14), and finally, the deepest compared to the next 

shallower (HS,H l 0,H 15). 

The results of ANOVA#1 showed only a modest number of significant 

differences. Of the sixty one species analyzed separately only twelve species showed 

significant regional variation among transects. Therefore, within the limitations of this 

analysis, there were few strong regional differences demonstrated . The conclusion that 

regional differences exist may be correct, but it is only weakly supported by this series of 

tests. The time-series design for yearly and seasonal sampling was extremely weak and 

limited only to the Central transect. Of the sixty one species sampled, only five showed 

significant spring-fall variation. The conclusion that seasonality exists may be correct, 

but it is ill-supported by this testing. Two showed significant inter-annual variation The 

weakness of the design makes any statement of dubious value. Even though two species 

did show significant effects, the study concluded that inter-annual variation was not 

significant. 

It is difficult to see the utility of the depth contrasts undertaken in the first 

ANOVA due to the confusion of the orthogonal contrasts method and the very 

inconsistent level of replication. In the Western transect which had only 3 replicates per 

station in Cruise I, the results of 61 separate species ANOVA could not reject a 

hypothesis of faunal homogeneity (no depth restriction) except for the two polychaetes 

Litocorsa antenna and Phole sp. C. It is to be suspected that the results are due to 

limited sampling. At the better sampled Eastern and Central transects, there were more 

definitive results, but again, the meaning is obscure. When the shallowest stations (series 

1) were compared to all the deeper (series 2,3,4 and 5 combined) only 10 of 61 species 

show significant differences across these dramatic depth boundaries. Are the boundaries 

105 
not distinct or was the comparison too unbalanced to be informative? The latter is 

suspected. The largest number of species showing significance differences were found 

when the most samples and most balance number of contrasts are compared. 

Table 3 .6 . Hypotheses and Applicable Samples for ANOVA #l . 

Hypothesis Applicable 

Transects 

Type of 

Question 

Statement of Hypothesis 

H, : E & W Regional Abundance Eastern = Western+Central 

H6: C & W Regional Abundance Central = Western 

Hii C Seasonal Abundance fall 83 = fall 84. 

Hz : E Depth Abundance E 1 = E2 through ES combined 

H3 : E Depth Abundance E 1 & E2 = E3 through E5 

H4 E Depth Abundance E2 = E3 

HS E Depth Abundance E4 = ES 

H7 W Depth Abundance W 1 = W2 throu hW5 combined 

H8 W Depth Abundance W1 & W2 = W3 throu hW5 

H9 W Depth Abundance W2 = W3 

H,o W Depth Abundance W4 = WS 

H,2 Cruise II C Depth Abundance C1 = C2 through CS combined 

H,3 Cruise II C Depth Abundance C1 & C2 = C3 through C5 

H,4 Cruise II C ' 

- 

Depth Abundance C2 = C3 

H,5 Cruise II C Depth Abundance C4 = CS 

H16 Cruise III C Depth Abundance C 1 = C2 through CS combined 

H17 Cruise III C Depth Abundance C1 & C2 = C3 through C5 

H,g Cruise III C Depth Abundance C2 = C3 

H19 Cruise III C Depth Abundance C4 = CS 

HZO Cruise IV C Depth Abundance C 1 = C2 through CS combined 

H21 Cruise IV C Depth Abundance C1 & C2 = C3 through C5 

H22 Cruise IV C Depth Abundance C2 = C3 

H23 ~ Cruise IV C ~ Depth ~ Abundance C4 = CS 

Of the 12 out of 61 species that showed significant inter-transect differences, the 

species in each of the two regional contrasts were different (Table 3 .7), making it unclear 

what it means. There may be a hint of higher populations on the Eastern Transect, When 

East is contrasted to the West, only 5 of 61 species show significant differences, with 

four more abundant in the East. However, an East to West gradient is less obvious when 

106 
C is contrasted to W. The 7 of 61 significantly different species are split four more 

abundant Central and three more abundant Western. 

Table 3 .7 . Twelve Species Showing Regional Differences and Direction of Abundance 

Differences Within Transects of ANOVA#1 ( ns= not significant) . 

Species Western Central Eastern 

Phole s C ns Less More 

Ceratoce halls oculata ns Less More 

Malletia s p. B ns Less More 

An ulorostrum s p . A ns Less More 

A seudidae ns More Less 

Tacht apes s .A Less More ns 

Maladne s p. A Less More ns 

Prionos io ehlersi Less More ns 

Prochelator s p.202 Less More ns 

Litocorsa antennata More Less ns 

Lumbrinerides da i More Less ns 

Ischnomesus sp.208 I More ~ Less ~ ns 

ANOVA#2 Depth Again 

ANOVA two was intended as a statistically rigorous examination of the 

Pequegnat (1983a) scheme of five faunal zones which determined the depth placement of 

the primary stations . In fall of 1984, 11 stations were sampled on the Central Transect, 

the original five plus an additional six to fill in the gaps. Unfortunately, the resulting gap 

filling did not correct for the progressively wider intervals of the original five stations . 

The stations still had greatly varying intervals, 200 m or less above 1200 m and about 

500 m below that depth. 

The hypotheses of ANOVA #2 dealt only with abundance on the Central Transect 

where finer scale sampling took place on Cruise III. There were ten variations of the 

same hypothesis of no difference in abundance. The variants of the hypothesis treated 

different depth comparisons . First, a shallower group of stations were contrasted to a 

deeper, and then those two groups teased apart in various combinations of ones, twos, 

and fours . These versions of the same hypotheses are presented along with the results and 

the stations combined in the contrasts are shown in table 3 .8 . 

Only 10 out of 61 species were significant across the major faunal transition, 

shallower versus deeper contrast As with the other ANOVA, interpretation is difficult 

and the final report avoided conclusions drawn on the results. However, the intent of 

testing the original zonation scheme was not carried out, and it is unclear what the finer 

scale sampling accomplished. The one suggestive finding was that there may be a greater 

107 
change in species between 1021 and 1192m than elsewhere. This might mean that 

Pequegnat's Archibenthal to Abyssal boundary does mark a depth of greater fauna 

change. 

The possibility of greater faunal change between 1021 and 1192m can be seen in 

pair-wise contrasts. When the five pair-wise contrasts are sorted out and ordered by 

depth and interesting pattern is exposed. Most notably, few of the 61 species show any 

significant difference, from none to six, depending on the particular contrast. The 

maximum number of six is found at two contrasts , the comparatively narrow depth range 

between C7 and C8 ( 1021, 1192m) and the wider range between C2 and C3 ( 633, 

881 m) . This can be cautiously taken as evidence that the species replacement rate is 

highest in this 1000 to 1200 m range . The results seem to point to rather uniform change 

otherwise. This is especially noted for contrasts between four shallower and four deeper, 

where each had 8 of 61 species being significantly different. 

Table 3 .8 . Ten ANOVA#2 Depth Contrast Hypotheses Tested on Central Transect and 

Results 

Hypothesis Taxa of 61 

with 

Significant 

Differences 

Stations Compared In Depth Order 

parentheses Indicate Groupings for Testing 

H, 10/61 1, 6, 2, 3 vs 7 ,8 ,9 ,4 ,11 ,5 ,12 

HZ 8/61 1,6 vs 2,3 

H3 2/61 1 vs 6 

H4 6/61 2 vs 3 

H5 4/61 7,8,9,4,11 vs 5,12 

H6 0/61 5 vs 12 

H7 4/61 7,8,9,4 vs 11 

Hg 7/61 7, 8 vs 9,4 

H9 6/61 7 vs 8 

o ~ 1/61 ~ (9) vS (4) 

ANOVA#3 Variation Across Isobaths in Eastern Gulf 

The third set of analyses was similar to the second in that there was a single 

hypothesis repeated in fifteen variants. The hypothesis tested on each of the sixty one 

species was of no significant difference in abundance between various parings of stations 

taken on the Eastern Transect. The hypotheses, the pairings, and the results are presented 

in Table 3 .9 . The NGMCS study attempted to phrase some of the fifteen hypotheses as 

addressing differences in substrate. Since these post hoc hypotheses were not anticipated 

in the original design, their results were ambiguous. 

108 
The results of the third set of ANOVA are as expected. When large numbers of 

stations at different depths were compared, relatively large numbers of significantly 

different species (19,15, and 11) were found. The fewer the stations contrasted and the 

more within isobath the contrast, the fewer significant species. Unfortunately, within 

isobath is confounded with fewer stations . It should be noted, however, that if the 

Pequegnat zones were very pronounced, many more of the dominant 61 species should 

have been significantly different. It appears on the basis of the limited design that few 

species reflect the zonation scheme . 

Table 3 .9 . Hypotheses, Number of Significant Results, and Stations Contrasted in 

ANOVA # 3 . 

Hypothesis Taxa of 61 

with 

Significant 

Differences 

Eastern Transect Stations Ordered by Depth 

Parentheses Indicate Groupings for Testing 

H, 19 la, 1, lb, lc vs 2, 2b, 2c, 2a, 2d, 2e, 3,3a,3b,3c,3d, 5 

HZ 3 la vs l,lb,lc 

H3 1 1 vs lb,lc 

H4 2 lb vs lc 

HS 11 2,2b,2c,2a,2d,2e, 3,3a,3b,3c,3d vs 5 

H6 15 2,2b,2c,2a,2d,2e vs 3,3a,3b,3c,3d 

H7 2 2,2b,2c vs 2a,2d,2e 

Hg 3 2, 2b vs 2c 

H9 1 2 vs 2b 

H,o 6 2a vs 2d,2e 

H 5 2d vs 2e 

H1Z 0 3,3b vs 3a,3c,3d 

H13 0 3 vs 3b 

H,4 1 3a vs 3c,3d 

3c vs (ML 

ANOVA#4 Variation Along Isobaths Between the Central and Western Transects 

Directed at the ancillary sampling between the Western and Central Transect, 

these analyses tested 11 orthogonal contrasts and the associated hypotheses. Here again 

the factors considered in the sampling design, depth and position in isobath were used. 

However, post hoc factors were also tested . These were sediment type, topography, and 

presence of seeps. As with ANOVA #3, these post hoc factors had not be sampled for in 

the design, and the results are ambiguous. An additional problem lay in the fact that the 

W-C series crosses both depth and position diagonally . The deepest stations lie near the 

109 
Central transect, while the shallowest lie near the Western. Depth and position are, thus, 

confounded . Hypotheses, station contrasts and results are shown in table 3 .10. 

The results were as expected for depth contrasts . The farther apart stations are, 

the more the abundance of fauna differs. This would be true for Pequegnat zonation or 

gradual change. That so few dominant species show this effect suggests that dramatic 

zonation does not exist. The other contrasts are hard to interpret. Within isobath 

comparisons and contrasts assumed to test topography, sediments, and seeps, there were 

from 1 to 8 significantly different taxa. Without proper replication the cause can not be 

identified . 

Table 3 .10. Hypotheses, Type of Question Asked, Number of Significant Species, and 

Samples Contrasted for ANOVA #4 . 

Hyp. Nature of 

uestion 

Significant 

Taxa of 61 

W-C Stations Ordered by W-E Position & Depth 

H, Depth 16 5,1,7,6,8,2,4 vs 9,10,3,11,12 

H3 Depth 14 5,1,7,6 vs 8,2, 4 

HS Depth 11 5,1 vs 7,6 

H6 Isobath-750 

m 

3 (9,10) vs (3) 

H7 Isobath-750 

m 

1 (9) vs (10) 

H,o Isobath-550 

m 

8 (8) vs (2,4) 

Hi, Isobath-550 

m 

5 (2) vs (4) 

HZ Sediments 6 5 vs 1 

H4 Topography 2 11 vs 12 

Hg See 7 7, 6 vs 5,1,4,8,2,3,9,11,12 

H9 Within See 6 7 vs 6 

3.7 Meiofauna 

3.7 .1 Introduction 

The meiofauna results of the NGMCS study are quite interesting and have 

management relevance if substantiated. Unfortunately, the archived data are reported 

only on a per station per cruise basis, and not at the sample level. The study reported 

more than 230,000 specimens in 43 major taxa with 98% consisting of nematodes, 

harpacticoid copepods, polychaetes, ostracods, kinoryncha, and naupliar crustacean 

larvae . Mean density was 700 org/10 cm2 ranging from a low of 200 to a high of 1,100. 

These values are among the highest reported (Thiel 1983). Initially proposed by Dr. R. 

110 
Titgen, the meiofuana component did not address specific hypothesis . Dr. Titgen left the 

project prior to completion. 

3 .7 .2 Methods 

Meiofauna samples were the top 5 cm of sediment in 4 core tubes mounted inside 

a GOMEX box corer. The tubes were 43.5 cm long and 3 .5 cm (also reported as 2 cm) in 

internal diameter. During the II through IV cruise, these cores were mounted against the 

wall of the core box, a location subject to washing. During Cruise I they were mounted 

centrally. The samples were narcotized in isotonic manganese sulfate for 30 min. then 

fixed with buffered formalin and stained with rose Bengal . Sampling effort is shown in 

table 3 .11 . 

The stations were as for the overall box coring programs. Western, Central, and 

Eastern regions each had main stations that consisted of a 5 station down-slope transect . 

Supplemental stations consisted of isobathyal transects of 12 stations each in the Western 

and Eastern Region. The supplemental stations at the Central region consisted of 7 

stations added to the cross slope transect. Biomass was not actually measured, but was 

based upon published values for similar taxonomic groups . This dependency upon 

published values was not tested and will not be considered in this reexamination. 

Table 3 .11 . Meiofauna Sampling Effort . 

Cruise WESTERN CENTRAL EASTERN 

Main 

Stations 

Suppl. 

Stations 

Main 

Stations 

Suppl. 

Stations 

Main Stations Suppl. 

Stations 

I 12at5 

II 6at5 12at5 6at5 

III 12at5 12at7 12at4 12at12 

IV 

V 12 at12 

Stations 5 12 5 7 5 12 

Pooled 

Tubes 

30 144 180 84 78 144 

3 .8 Megafauna Trawl and Photo 

3 .8 .1 Introduction 

Megafauna have already been discussed with respect to an estimation of how 

species rich the group might be (section 6), and how some species contribute to the 

scheme of bathymetric zonation proposed by Pequegnat (1983a). This section focuses on 

the remaining topic of density estimates based upon trawling versus those based on 

photography. 

111 
The megafauna data summarized by Pequegnat (1983a) are probably the most 

extensive study of that size class for any deep ocean region . The Gulf samples are unique 

with respect to the ninety four skimmer samples that preserved fragile specimens in 

excellent condition. The taxonomic detail devoted to the material was also excellent . 

This same care was expended upon the megafauna of the NGMCS. Sampling of 

megafauna by trawl in the NGMCS study followed essentially the same design as box 

core sampling, but did not replicate within stations . As a result there was a total of 58 

samples (Table 3 .12) . 

Table 3.12. Executed Trawl Sampling Design 

Cruise WESTERN CENTRAL EASTERN 

Main 

Stations 

Suppl . 

Stations 

Main 

Stations 

Suppl. 

Stations 

Main Stations Suppl. 

Stations 

I 1 at 5 

11 1 at 5 1 at 5 1 at 5 

III 1 at 5 1 at 6 

IV lat3 1at12 

V 1 at 12 

Stations 5 12 5 6 5 12 

Trawls 5 12 15 6 8 12 

3.8 .2 Photosurvey 

During the first cruise of the NGMCS Study, bottom photography was conducted 

by the Deep Submergence Engineering Group at WHOI under direction of C.M. Young. 

These initial and subsequent bottom surveys were conducted with a 800 frame Edgertontype pressure housed 35mm camera and strobe system purchased from Benthos Inc. 

Initially configured as a "mini Angus System", the camera package was suspended on a 

hydrowire and kept near a depth 2m above bottom. During Cruise I depth above bottom 

was determined acoustically on the surface. The pinger on the camera package produced 

a double ping with the time lag between pings being controlled by an acoustic altimeter 

on the frame. The "mini Angus" had not previously been used for quantitative biological 

sampling, and the lack of reference between height and actual photo image proved to be 

inadequate for the task. For cruises II-V, LGL obtained its own Benthos system modified 

such that the height information was both telemetered and recorded on the film data 

recorder . Analysis of the images was conducted by G. Boland with data processing and 

management by J. Baker. 

Sixty surveys were conducted producing a total of 48,000 images. The length of 

survey was determined by drift rate, ranging from 1500 to 5000 m long. Excluding 

Cruise I results due to poor altitude control, Each 800 exposure film roll was subsampled 

employing the method of Cochran(1977). For Cruise II, 100 subsamples were used. This 

was increased to 200 on subsequent cruises. Images were then projected onto a Houston 

Instruments DT- 11VA digitizer. In addition to general information about the image, six 

112 
data categories were considered : (1) invertebrates, (2) fishes, (3) man-made items, (4) 

terrigenous and nearshore material, (5) consolidated material, and (6) lebenspurren . The 

examination of lebenspurren ( tracks, trails, etc.) was conducted only on cruise II and III 

images. This special analysis employed 2321 images representing about 6569 mz of 

bottom Of the 44,000 images (45 stations) taken after Cruise I, 9,147 (24,590 mz of 

bottom) were analyzed for fauna. Data has been derived for about 20% of the images. 

The films are archived at LGL Ecological Associates Inc . 

3 .8 .3 Megafaunal Biomass: Two Estimates and Possible Special Habitats 

Two means of estimating megafauna biomass exist from the NGMCS Study, 

bottom photography and trawling . A simple comparison of the two (figure 3 .6) produces 

different results . Trawl sampling reveals a wide range in faunal density estimates . With 

only eight samples taken below 1000 m, there is not a good basis for establishing depth 

trends, however there is some indication of a decrease with depth. Distinctly different are 

the photograph-based data. Total fauna density estimated from photographs tends to be a 

full order of magnitude greater than trawl estimates. There is also an indication of a very 

wide biomass range at mid depths (1000-2000 m). 

D 

t 1CCY3 

i 

n 

M 

t 2000 

z 

r 

s 

A ~n ~~or~ ~ ~ Extreme Da.^.sisies 

m ~ o o~~,,:~ 

a~A 14 o pt C_7 

0 

A ~,7 

6.A 0 0 C-4 

to 

C1 C-1C 

A O 

e D I 

A -Tr~rrl Steles 

0 ----- Phr0tcsusvsY 

2 3 4 5 f 

Log -%, 0{anink~ls-11h ac tara} 

_ ._ ._

._------------------------------------------- -- - - - - ------- ._ . .__ . . ._ . . ._ .---- ._ .. . . . . . . . . . . . . . ._ . . . . ._ . . . . . . . .---------------- . . . . .. ._. . ._ . . .. . . .--------- . . .. .i 

Figure 3 .6. Megafauna Density Estimates Based on Photosurvey and Trawling. 

On examination, it is found that only four camera stations contribute to the 

appearance of a mid-depth abundance increase . All in the central transect, each of these 

four represents a special case: 

113 
C-9 Of a reported 156,344 animals hectare, 154,800 were the patch forming 

holothuroid Peniagone. 

C-7 Of a reported 57,151 animals hectare, 51,566 were bivalves identified as 

dead and possibly living vesicomyidae at a seep site . 

C-4 Of a reported 41,011 animals hectare 40,212 were again Peniagone. 

C-10 Of a reported 22,697 animals/ hectare 16,514 were sponges . 

In each of these four cases, the high densities were due to unusually high values 

of a single species or restricted taxa. At C-7 it is clearly associated with proximity to a 

chemosynthetic system . Although it is suggested in the NGMCS reports that the 

Peniagone stations might be related to seeps as well, this now seems unlikely since 

Peniagone has never been encountered during any of the subsequent manned seep dives. 

Rather than attempting to explain everything in terms of seeps, it seems more reasonable 

to consider the possibility of additional unique habitats. For instance, sponge 

aggregations have been observed during Alvin dives in the Gulf of Mexico below 2000 

m. The tremendous topographic complexity of the continental slope in the area of the 

Central transect could easily give rise to such habitats . The camera survey may have 

sampled special topographically controlled biota. Possible mechanisms for control might 

be topographically enhanced and steered bottom currents, recent slumping events, or 

sediment instability on the slope . In these same proposed special habitats, the trawl may 

have failed to sample, or have successfully sampled, but then obscured the discrete nature 

of the habitat as it trawled over a much larger area. 

3 .9 Macrofauna 

Macrofauna have become the primary source of faunal data for soft bottom 

systems. This is due to the fact that they can be sampled quantitatively, they are sampled 

coincidentally with the sediment they live in, and they produce sample sizes more 

appropriate for statistical analysis. Pequegnat (1983a) devoted little attention to this size 

class. Therefore, the NGMCS constitutes the primary study of deep Gulf of Mexico 

macrofauna . In the reanalysis undertaken, greatest emphasis was placed on diversity and 

density estimates since the conclusions of the NGMCS report seem to be in error. There 

will be no additional discussion of zonation. As stated earlier, the depth of samples was 

poorly suited to zonation analysis, the ANOVA suggest few macrofauna species show 

distinct zones, and reanalysis of zonation has shown the limited degree to which 

macrofauna participate in bathymetric zonation. 

3 .9 .1 Macrofauna Diversity 

The NGMCS study concluded that macrofauna diversity in the Gulf of Mexico 

was less than that of the ASCAR studies of the Atlantic. Additionally, the Gulf shows no 

depth maximum. The reanalysis of the restructured data archive reported herein, finds 

that the deep Gulf is markedly more species rich than the western Atlantic, but confirms 

the lack of a depth maximum. 

The reanalysis of species diversity differed from the NGMCS study in three 

important ways. First, macrofauna-sized nematodes and harpacticoid copepods were 

114 
included in the reanalysis . This can be expected to add many specimens to a sample 

count but only two taxa, lowering computed diversity. Second, counts of taxa identified 

only to genus were also included, increasing computed diversity. Third, the basis of 

comparison was Hurlbert's (1971) method of rarefaction (Hayek and Buzas 1997). By 

contrast, the NGMCS calculated information-based diversity (H), excluding nematodes, 

harpacticoids, and unresolved species. 

When the macrofauna sampled on the north eastern Gulf continental slope is 

compared with previous shelf studies using the data archives of those studies (Carney 

1993), the expected pattern of higher diversity with depth is found (Figure 3 .7). Even 

though shelf surveys have typically produced twice to three times the 69,161 specimens 

of the NGMCS program, they produce only 50% to 60% of the species number. It is 

reasonable to conclude that diversity maintaining processes in the deep environment are 

different in some manner from those in shallow water. By extension, the effect of 

impacting agents in deepwater may not be the same as has been experienced in shallow 

water. In drawing this conclusion, it must be assumed that diversity differences are not 

simply an artifact of sieve size, 300 micrometer for deep samples versus the 500 

micrometer for shallow. 

Two of the shelf studies used for comparison surveyed relatively monotonous soft 

sediment bottoms and produced remarkably similar results of 700 to 800 macrofauna 

species. The best documented shelf study in the Gulf of Mexico is the South Texas 

Baseline Study (STBS), also called the South Texas Outer Continental Slope (STOCS) 

study in some references. Samples were taken 1976-77 with a 0 .1 m2 Smith-McIntyre 

grab and samples sieved at 500 micrometers. An open literature publication provides the 

main findings (Flint and Rabalais 1981), but the final technical report (Flint and Rabalais 

1980) provides the most informative detail . Complementing the STBS study and 

employing the same basic techniques was the Central Gulf Platform (CGP) Study in 

1978-79. CGP samples were taken on the continental shelf off Louisiana in a region of 

oil and gas activity . The final technical report (Bedinger 1981), is the primary reference. 

It is interesting to note that on the southwest Florida shelf, which is a patchwork of hard 

and soft substrates, that higher diversities were encountered. Overall species richness 

was, however, lower than found on the continental slope. These data came from the 

Southwest Florida (SWFL) study which began in 1980 . A 0.057 m2 box corer was used 

augmented by diver-collected samples, and a 500 micrometer sieve employed. 

There has been a great deal of discussion focused upon the fact that the slope and 

rise macrofauna sampling of Sanders and Hessler found a deep diversity maximum (Rex 

1983). This modal pattern is now considered one of several large scale marine and 

terrestrial diversity gradients where there is a maximum, parabolic diversity patterns . 

The NGMCS study did not report a diversity maximum. This apparent finding that the 

Gulf differs from the adjacent Atlantic is quite important. If valid, it would indicate that 

diversity maintenance in the Gulf may be unique. 

115 
. 

NGMCS 

J 

I .ag Shelf 

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Figure 3 .7 . Rarefaction Curves Contrasting the Deep Macrofauna with Regional 

Gulf of Mexico Continental Shelf 

Contrasting the NGMCS data archives with those of the ACSAR archives 

provided a means of checking the apparent absence of parabolic diversity in the Gulf. 

Since the NGMCS Study employed a 0.06 m2 sampler rather than the more standard 0.09 

m2 sampler used in the ACSAR program there is an obvious problem of comparisons 

between unequal sample sizes. Conceptually and computationally complex methods of 

adjusting for such inequalities are rarefaction and abundification (Hayek and Buzas 

1997). For our purposes however, a simpler approach is taken using the ratio 

taxa:specimens. This value provides a simple appreciation for how species rich a sample 

is (Figure 3 .8). 

A regionally complex parabolic diversity pattern is present. In the Southern series 

species: specimens increase progressively with depth and are maximum at 3000 m. The 

Middle series has a smaller depth range, but species: specimens increases with depth and 

appears to be maximum at 2000 m. The Northern series has high values with a maximum 

at about 2500 m. However at the 1000 m level in that series, there are also some high 

values which depart from the parabolic pattern. 

When the NGMCS archives are considered there is no conspicuous depth trend 

(Figure 3 .9). The apparent uniformity with depth is underscored by the fact that these 

326 values have a very well defined mean of 63.57f 23 .48 species per sample in spite of 

the fact that they spanned almost 3000 m of depth. The finding of the NGMCS study of 

no parabolic depth pattern seems valid. The significance of this is very hard to assess, 

116 
since we do not know what causes the parabolic pattern. It may be due to an underlying 

pattern of unusual species depth ranges . Unfortunately, the spacing of samples does not 

allow for the assessment of this . 

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Figure 3 .8 . Sample-level Diversity Trends in the Western Atlantic . 

Highly Diverse Deep Gulf? 

A comparison of the total fauna inventory developed during the NGMCS Study 

with that of the ACSAR study reveals an intriguing pattern (Figure 3 .10) . The northern 

Gulf seems to have a more diverse macrofauna than the Atlantic . This is first suggested 

by the length of the inventories. The three regional components, North, Middle, and 

South, of the ACSAR Study yielded 1,233, 1,056, and 1,430 taxa respectively . NGMCS 

study produced 1,613 . That these species richness reflect real differences is supported by 

the total number of specimens collected. Due to its small core size, the NGMCS Study 

yielded the smallest overall collection of 69,161 specimens. The components of ACSAR 

yielded appreciably higher values of 108,275, 99,067, and 103,719 . 

This result suggests that diversity control on the Gulf continental slope may be in 

some way different than off the East Coast. It is highly management relevant and requires 

careful evaluation . There are five factors which might cast doubt on the finding. 

However, when the consequence of each is considered only taxonomic resolution poses a 

serious problem. 

1 . Different Sampling Devices and Methods - Even though the ACSAR study 

used 0 .09 mz from a 0.25 m2 box cores and the NGMCS study used smaller 

117 
yoked 0.06 m2 cores, this difference should not bias results in the direction 

observed. There is no obvious means by which a larger core would capture 

fewer species, and a smaller core capture more. 

2. Different Processing Methods - Both projects reported similar processing 

methods, and any biases arising at the execution level would be biased 

against the observed pattern. 

3 . Taxonomic Resolution - The two studies utilized different taxonomic experts, 

and no standards exist for assessing taxonomic error. 

4. Insensitivity of H' Diversity Index - The NGMCS elected to compare diversity 

using the information-based statistic H' . This index is most influenced by 

species comprising about 33% of a sample and is insensitive to rare species. 

It is an inappropriate choice for deep-sea samples where numerous rare 

species can be found in a sample. 

5 . Data Culling - The NGMCS study limited diversity index calculation to only 

those taxa fully identified to species and eliminated macrofauna-sized nematodes and 

harpacticoid copepods. This effectively eliminated 25% of all taxa. 

-- 

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Figure 3 .9 . Sample-Level Diversity Trends in NGMCS Study. 

118 
Cix . . . . . . . . . . . . . . . . . . . . . . . . . . . . ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .,. . . . . .,. . .. . . .. ...,.. .. .,.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. ... .. 

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Figure 3 .10. Rarefaction Curves for Gulf and Atlantic Macrofuana. 

Until the issue of taxonomic resolution is resolved, the finding of higher diversity 

in the Gulf must be considered tentative. The best confirmation of the pattern would be 

to undertake comparative Gulf and Atlantic sampling using the same techniques and 

personnel. The extent of sampling needed, however, may be fiscally prohibitive . An 

adequate alternative would be resume sampling in the Gulf with the entire collection of 

targeted taxa, not just vouchers, sent to experts who participated in the ACSAR study. 

The decade that has passed since completion of ACSAR may make this difficult. 

3 .9 .2 Macofaunal Density Comparison 

It was stated by Rowe and Menzel (1971) on the basis of a few samples that the 

Gulf of Mexico has low standing stock macrofauna biomass when compared to other 

oceans . The NGMCS considered this statement and failed to reject it, but no formal 

comparison with other data were undertaken. If true, it could mean that the deep Gulf of 

Mexico experiences greater-than-usual food limitation and is especially susceptible to 

impact by activities which alter the detritus influx and distribution processes. Due to this 

potential for management relevance, a reanalysis was undertaken here . 

119 
120 

The method of comparison is primarily graphical with statistics used for description 

rather than testing. Such a cautious approach is appropriate given the methodological differences 

in the studies compared. A comparison of the depth pattern of total faunal counts in the 326 box 

cores in the NGMCS data archives versus those of the 558 box cores in the ACSAR archives 

produces results that are difficult to interpret (Figure 3.11). 

Macrofauna Sample Density, log10(counts/m2)

D

e

p

t

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i

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M

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Gulf 

Samples

Atlantic

Samples

GULF ATLANTIC

Figure 3.11. Comparative Depth Decrease of Macrofauna Densities. 

The macrofauna counts for the box cores of the Atlantic Continental Slope and Rise study 

(ACSAR) provide a basis comparison of faunal density between the Atlantic slope and that of 

the Northern Gulf of Mexico Continental Slope study in the Gulf of Mexico. Expressed in the 

common form of counts m-2, the Gulf appears to have dramatically lower faunal abundance. 

Atlantic samples were obtained from the Battelle data archive. The Gulf of Mexico data 

were obtained from the restructured NGMCS data archives. Linear regression was carried out on 

log transformed densities, taking depth as the independent and density as the dependent value. 

In the oceanographic tradition, depth is plotted on the y axis. The scatter of the data overlaps, 

but there is an indication of different trends that can be illustrated with regression lines. The 

resulting lines were produced: 

W. Atlantic Macrofauna Density = 4.159 - 0.00026z ± 0.256, n= 558 

N. Gulf of Mexico Macrofauna Density = 3.712 - 0.00013z ± 0.279, n= 326 
In the NGMCS Final Report, a similar regression was reported based on 

composite stations . The value of that function, which gave no variation term, was: 

Station Level Macrofauna Density = 3 .52 - 0.00019z 

The differences are easily attributed to inclusion of macrofauna-sized nematodes and 

harpacticoids in the reanalysis . 

Being cautious not to over-interpret the results, an interesting contrast can be 

seen. Above 2000 m the Gulf appears to have lower macrofauna density. The rate at 

which density declines with depth in the Gulf is apparently less than in the Atlantic . 

Below 2000 m densities become more similar. Food input rates and types may differ 

between the Gulf and the NW Atlantic. It is a possibility that should be specifically 

addressed. 

3 .10 Conclusions and Recommendations 

In this final chapter the conclusions based on the reexamination and synthesis will 

be presented along with recommendations that come from them. Prior to presenting these 

new points, the recommendations presented by Pequegnat (1983a) and the NGMCS 

Study (Gallaway 1989) will be considered. Many of those are still quite valid. 

3.10.1 Recommendations of Pequegnat 

The Pequegnat report concluded with a list of recommendations for action that 

would minimize deep-sea impacts due to oil and gas development. He also provided a 

list of investigations to fill information gaps. 

Pequegnat's (1983a) report concluded with a list of actions that could be 

voluntarily undertaken by industry or imposed by MMS. These are still worth 

considering, although technology development have made some outdated . Below they 

are classified by type, paraphrased, and commented on. The list has be reordered to give 

it a sense of contemporary priority . Only three of the recommended actions deal directly 

with ecology. Four are related to hazard reduction. 

1 . Ecology - Ecological monitoring should be initiated before and during specific deep 

development projects to provide information about effects. 

This remains an excellent recommendation made more than a 

decade before any development was started. 

2 . Ecology - Undertake surveys of the slope environment including fauna, currents, 

water mass properties, and studies of turbidity tolerance. 

The NGMCS study met some of these needs. Studies of the 

turbidity tolerance of deep animals is a good idea but poses 

technological challenges . 

3 . Ecology - Buffer zones should be provided between major areas of development to 

provide refuges which can be the sources for repopulation of 

impacted areas. 

121 
A similar provision for refuges was mandated for manganese 

nodule development. It is difficult to envision that deep 

development will be more dense than on the continental shelf, 

where there is no evidence of large-scale impact . 

4. Geohazard - Limit leasing to areas of more stable bottom until technology of drilling 

is more advanced. 

Concerns about accidents associated with drilling on unstable 

slopes are still valid . However, there is so much technological 

development that a leasing prohibition is not called for at this time. 

5 . Geohazard - Limit drilling on unstable bottom to seasons of better weather 

conditions so as to minimize risks. 

Highly effective dynamic position and use of seafloor templates 

have effectively eliminated this concern. 

6. Safety - The safest known technologies should be used. 

This is how both industry and MMS operate; no new policies are 

needed unless new hazards are found. 

7 . Blowout Control - Technology should be developed to minimize damage. 

This is still a valid suggestion . There has been substantial 

development in these areas. 

As a framework for studies, Pequegnat felt that there should be interdisciplinary 

study of the Gulf stressing biological and physical data. Of particular interest to him 

were determination of standing stocks and secondary production using his zonation 

scheme as a basis for sampling. Physically, the residence time of deep water should be 

determined ("flushing rate") . Specifically related to oil pollution, chemical finger prints 

in animals and sediment should be examined. Following this general framework, specific 

information voids were identified . These gaps have been shortened, rephrased, and 

reconsidered below . Basically, all the information gaps identified in 1983 still exist. 

l . Chemical - Organic detritus flux through the water and in the sediments should be 

measured. Measurements should included studies of benthic 

consumption. This information is still needed. 

2. Physical - A synoptic picture of at and above bottom currents must be obtained. This 

would include topographic steering. This information is still 

needed. 

3. Geological - A more extensive and geographically broader understanding of the 

frequency and magnitude of mass transport is needed. This 

geological work also needs to address natural effects on fauna. 

4. Ecological - a . It was felt that megafauna had been adequately surveyed. Future 

surveys should focus upon macroinfauna and meiofauna but not 

exclude other groups . In addition the benthopelagic fauna should 

be considered . This is essentially how the NGMCS study was 

structured . 

122 
b. Surveys should focus upon specific topographic features such as 

DeSoto Canyon between 2250 and 2700 m, Mississippi Trough at 

all depths, and Alaminos Canyon . Feature-specific sampling 

seems highly appropriate due to the complexity of the Gulf of 

Mexico. Increased use of submersibles, and controlled towed 

instrument packages now make this more feasible. 

c . Sampling in all areas should help fill the 2200-2750 m gap. This is 

a good recommendation, however the gap actually begins much 

shallower at about 1500 m. 

3 .10.2 Conclusions and Recommendations of the NGMCS Study 

In the summary of the NGMCS study (Gallaway 1989) the conclusions were 

limited to the final testing of seven hypotheses . The primary evidence for a judgement of 

the first four hypotheses came from the multiple contrasts analyses of variance discussed 

in section seven of this report . 

1 . It was rejected that the Gulf lacked geographic regions. The eastern Gulf was thought 

to have greater endemism and higher biomass. The western region was 

distinguished by chemosynthetic communities . Physical conditions were thought 

to cause some of these differences. 

This reevaluation found these to be poorly supported conclusions. While east-towest differences may occur, fewer than 1/5th of the dominant species showed any 

suggestion of such a pattern in the ANOVA run. The issue of endemism is 

greatly complicated by uneven sample designs. 

2 . It was concluded that there was no annual variation. 

Reevaluation found this to be an acceptable conclusion . The time-series sampled 

was very short. 

3 . It was concluded that there were seasonal fluctuations in populations. 

Reevaluation found this to be a weak conclusion found in only a few species in 

the ANOVA. The fall - spring contrast over just two years was too short of a 

sampling period . 

4. It was concluded that there was significant difference in faunal composition with 

depth. 

This conclusion was supported by many of the multiple comparisons rather than a 

single strong analysis. It was consistent with what we already known about the 

deep sea and is most certainly correct. 

5 . It was concluded that there were no significant differences within faunal zones . 

Reevaluation found that the tests were unbalanced as poorly suited to detect 

within zone variations . 

6. Is was concluded that the Gulf slope was less productive than other slopes in the 

ocean. 

123 
Reevaluation of macrofauna densities supports this contention above 2000 m. 

Below that, inter-basin densities become similar. For meiofauna, the Gulf may 

have very high densities. 

7. It was concluded that there were atypical slope habitats, as evidenced by the 

chemosynthetic communities . 

Confirmation of this finding is obvious. In addition there was indication of deep 

sponge banks and large patches (100's m2) of the holothuroid Peniagone in the 

NGMCS study. The Pequegnat studies found patches of unknown size where sea 

urchins predominated . 

The primary recommendations of the NGMCS study addresses inadequacies of 

sampling rather than addressing more general gaps in environmental information. All the 

recommendations are still valid. 

1 . Sample sizes should be increased to improve the power of the analyses . This means 

larger samplers and replication. 

On reevaluation it has to be generally agreed that more replicates are better than a 

few. However, deep populations have so many rare species that there will never 

be an end to demands for more replicates . A better use of resources would be to 

increase size ; employ a 0.25m2 box core, and keep replication at about five cores . 

Increasing trawl size is impractical, making increased replication preferred in 

megafuana studies. Over the range sampled, a fixed depth interval should be used 

that do not presume a particular zonation scheme. 

2 . Photosurveys of tracks and traces were concluded to be marginally useful, but imagebased surveys of special habitats were seen as essential. 

On reevaluation this is still a valid consideration. Rather than abandon surveying 

of lebenspurren, it would be preferable to undertake development of more 

informative techniques . 

3 . Future studies should anticipate the considerable workload associated with sorting and 

identification of species-level samples from the deep sea. 

This is still a valid concern. It has been over ten years since MMS supported an 

extensive deep-sea survey, and the pool of taxonomic experts is now less than 

before . Either robust methods which do not require species-level work must be 

developed or the increasing costs of deep studies accommodated. 

3 .10.3 Conclusions and Recommendations of this Review 

1 . Megafauna - Pequegnat's conclusion that the larger fauna was well known and 

adequately surveyed is challenged by the fact that the NGMCS study collected 

many different species and produced major differences in the estimation of 

relative abundance . The large number of rare species in the Pequegnat and 

NGMCS megafuana inventories indicate that the fauna remains under sampled. 

This gives rise to two management concerns. First, there may be additional 

special habitats discovered such as chemosynthetic communities and sponge 

124 
banks. Second, there may be species encountered which attract public interest 

and raise environmental concerns. 

2. Macrofauna - The NGMCS is the only comprehensive survey of this size group in the 

Gulf of Mexico . The possibility of very high species richness requires that much 

basic taxonomic work needs to be done in this region . The primary management 

concern lies in the fact that macrofauna have become the primary data source for 

monitoring and impact studies. Therefore a high degree of understanding of the 

natural variation of this group is needed. 

3 . Meiofauna - The meiofauna component of the NGMCS study was well designed, but 

only executed at a low level of taxonomic resolution and archived only at the 

station level. The very high densities of meiofauna, mostly nematodes and 

harpacticoids, warrant additional study. 

4. Zonation - There is no doubt that fauna changes with depth much more than it changes 

along isobaths . This was well confirmed by Pequegnat, the NGMCS study, and is 

quite obvious from a reexamination of the data. The emphasis on a specific 

scheme of zonation is misdirected. Zones are very useful to management because 

they define regions which require specialized plans. The use of zones in 

understanding ecology is less well established, and efforts to carefully delineate 

zones by sampling quickly run into confusion as to what are meaningful and what 

are random patterns. Physically, there is good reason to treat the legally defined 

deep sea (deeper than 200 m) as having at least two major divisions . An upper 

zone from 200 m to 1000 m experiences physical variation and lies in the region 

of low oxygen. A deeper zone is physically distinct and contains a fauna that 

shifts progressively to deeper-dwelling species. 

5 . Diversity - The Gulf deep macrofauna are more diverse than the shelf environments. 

Based upon rarefaction, the Gulf slope has a greater species richness than the 

coast of the Atlantic states . This conclusion must be qualified by the fact that the 

compared studies differed in many important ways. 

6 . Abundance - The reexamination found a depth-density relationship similar to that 

reported in the NGMCS study. Two differences were quite important. First, Gulf 

macrofauna densities above 2000 m are lower than found in the ACSAR study, 

but become similar below that . Second, the rate of density decline with depth in 

the Gulf appeared to be slower, suggesting a greater influx of food to deep water. 

As with the diversity conclusion, it must be cautioned that this comparison looks 

at data from studies that differed in important ways . 

7. Special Habitats - In addition to the conspicuous chemosynthetic communities there 

appear to be other distinct deep habitats. Megafauna show dense patches of 

sponges, echinoids, and holothuroids . Being sessile, it can be assumed that the 

sponge banks are long-term features. The persistence of the echinoderm patches 

is more problematic in that both echinoids and some holothuroids are capable of 

short-term aggregation. The view that deep fauna is homogenous is not 

supported. 

125 
3 .10.4 Recommendations of This Review 

Since this review was begun, deep oil and gas leasing has increased substantially. 

In response, MMS has worked with industry and the research community to identify 

needs and concerns. Some of these needs have been formally identified (Carney 1998) 

and already acted upon. The list of recommendations given here are not intended to 

replace those developed through other processes. They are limited to the information 

gaps found upon reexamination of the ecological data. 

1 . Maximization of Data Quality - For both the NGMCS and ACSAR studies, the 

required filing of NODC databases did not produce a useful and accessible 

archive. 

MMS should review this requirement in conjunction with NODC and adopt new 

procedures that accomplish that need. The archives of both studies should be 

recreated and updated. 

2. Standardization of sampling gear - The Gulf of Mexico may emerge as the primary 

region of the world ocean where human impacts on deep systems are studied. It is 

imperative that data collected in the Gulf be comparable to the best collected 

elsewhere . 

The main area in deep-sea ecology where there has been some degree of 

standardization is macrofauna. Future sampling must make use of a 0.25 m2 box 

corer. The 300 gm sieve should still be used to process the macrofauna. Any 

departure from this standard carries the obligation to convincingly demonstrate 

the value of the technology and provide a means of comparison with older data. 

The conclusions in this report that the Gulf is more species rich than the Atlantic 

and of similar biomass should be tested with appropriate gear. 

Geographic Range of Study - MMS has a mandate only to study US waters, while the 

Gulf is so small that the ecology in one region may be impacted by processes in 

Mexican , Cuban, or even Caribbean waters . 

A means needs to be found to study basin-wide processes. The east-to-west 

differences proposed by Pequegnat were not adequately examined by the NGMCS 

study. The region east of the Mississippi should be carefully compared to the 

western slope of the Gulf off Texas and Mexico. 

4. Bathymetric Range of Study - Deep sampling in the Gulf has been concentrated in 

shallower than 1500 m with most above 1000 m. Deeper than 1500 m sampling 

effort has been unequal. 

This lack of equal effort distorts results and leaves the recognition of faunal 

change at greater depths open to subjective interpretation. Future sampling 

should focus deeper than 1500 m. The depth sequencing of samples must not 

presume a given depth zonation scheme. Fixed depth intervals or randomization 

with bands of fixed width are preferred. 

5 . Special Habitats - It is obvious that the deep Gulf is a topographically, physically, and 

chemically complex environment with distinct habitats ranging from the obvious 

to the subtle . 

126 
The faunal changes associated with these features may confuse impact studies, 

and some habitats may warrant protection. High resolution topographic data for 

the northern Gulf is now being made available by the National Oceanographic 

Data Center, making feature specific studies feasible. Future studies should be 

designed to compare canyon walls and floor, topographic highs and lows, slopeprone regions and stable regions. Efforts should be made to relocate the sponge 

banks, holothuroid aggregations, and echinoid aggregations to determine longterm persistence. 

6. Optimization of Design - Studies that frequently change the intent of sampling often 

end up unable to undertake convincing identification of patterns. 

The alteration of sampling to pursue arising questions result in a data set that 

allows few of the main questions to be answered effectively . Future sampling 

should target known features. Sampling should be stratified within the structure 

of such features testing explicit hypotheses about faunal pattern. Once a feature 

or series of features has been identified, and the hypotheses stated, then 

replication can be designed accordingly. Unfortunately, species-level analyses 

may require a prohibitive level of replication. In such a case, a general ecological 

parameter such as biomass or a process such as secondary production may be 

used. 

127 

4 Extension of Chemosynthetic Fauna Disturbance Monitoring 

4.1 Introduction 

As introduced in Chapter One, the first question facing oil and gas environmental 

management is how appropriate established management strategies for the continental 

shelf are for the deep ocean? To answer this question, we start by determining how much 

alike and dissimilar the environments are, and we find that in certain respects the faunae 

differ only by degree . There are, however, few parallels between deep-water 

chemosynthetic communities (VanDover 2000) and any shelf-depth assemblage. 

Appropriate management of these systems is a unique challenge to MMS. This chapter is 

different than the previous two in that it is intended to make a modest contribution of new 

information about chemosynthetic (more widely termed chemoautotrophic) communities, 

rather than review and critique previous studies. The time for a comprehensive critique 

from a management perspective is drawing near, but all initial results are not yet in. 

The chemoautotrophic communities associated with hydrocarbon seeps of the 

Louisiana continental slope have been under almost continuous study since their 

discovery (Kennicutt et al . 1985, Rossman et al. 1987). Recognizing the "reef-like" 

status of these systems, MMS has sought to gain management-relevant information 

through a series of field studies . Initial investigations were begun as a supplemental task 

of the NGMCS and then expanded into the Chemosynthetic Ecosystems Study 

(MacDonald et al. 1995) followed by the Stability and Change in Gulf of Mexico 

Chemosynthetic Communities (MacDonald submitted). These studies, usually referred to 

as Chemo-I and Chemo-II, have been completed . A more modest effort is still ongoing 

under the Coastal Marine Institute Program, Improved Geohazards and Benthic Habitat 

Evaluations . 

In terms of new information, this chapter does three things . It was the objective of 

this task to extend the geographic range of hydrocarbon seep sites considered by 

MacDonald et al . (1995) and extend the time of observation of markers left at seep 

community sites. Accordingly, dive tapes have been reviewed for 42 dives in 24 bottom 

areas studied by Roberts and Carney (1997) and collections from 13 dives sorted and 

identified . The status of markers left to aid recognition of long-term change was also 

updated to 1997. 

4.1 .1 The Contrast of Two Projects 

In 1989, five years after the initial discovery of vent-type fauna off the Louisiana 

coast (Kennicutt et a1 .1985, Rossman et al . 1987) two largely separate groups of 

researchers began a decade long series of studies at hydrocarbon seep sites. The first of 

these, employing a strongly geochemical and ecological approach, was a multi-university 

project lead by the Geochemical and Environmental Research Group (GERG) of Texas 

A&M University . The second, lead by the Coastal Studies Institute (CSI) of Louisiana 

State University (LSU), took a strongly geological approach. The CSI effort examined 

seeps in the larger context of long-standing questions about slope dynamics and 

authigenic carbonate precipitation. Due to the different orientations the two programs 

129 
have selected dive sites by different criteria. GERG's ecological studies required sites 

that could sustain repeated scientific collecting and long-term experimentation. The CSI 

studies had minimal biology components, and selected sites so as to sample a wide range 

of geological structures with few returns to the same site . 

Critically examined, neither focus (largely ecology versus largely geology) by 

itself can provide a full picture either in terms of management or basic ecology. The 

needs of the GERG group have lead them to repeatedly sample systems that have been 

persistent enough through time to build up high population densities. These studies 

provide an unequalled understanding of the biology of such stable communities, but they 

contribute less to a broader understanding of persistence and stability. The needs of the 

CSI group have lead them to explore a greater variety of geological features. These 

explorations allow for a broader synthesis to be developed, but they lack sufficient detail 

to be certain that the ecological aspects of the syntheses are valid. It is the purpose of this 

small study to improve the ecological value of the CSI seep investigations so those results 

may be combined with the ecological studies of the GERG group. 

4 .1 .2 Characterization of the Assemblage Across Sites 

Previous Work and Expectations of Faunal Difference 

The primary work on northern Gulf chemosynthetic communities is summarized 

in MacDonald et al . (1995) and MacDonald (submitted). Extensive diver observation, 

opportunistic sampling, and 61ANOVA-designed faunal samples (submersible scoop) 

determined the basic faunal patterns at four primary sites: Green Canyon 185, Bush Hill ; 

Green Canyon 234; Green Canyon 233, Brine Pool; and Green Canyon 272. Two 

additional sites were sampled less extensively: Vioska Knoll 826 and Garden Banks 386. 

All except the Brine Pool were mixed communities of tube worms and mussels on 

exposed and superficially buried carbonates . During Chemo-I only mussel beds were 

effectively sampled. The taxonomic status of the mussels is relatively well known 

(Gustafson et al . 1999). Mat-forming mussels were a mono-species populations of the 

methane-utilizing Bathymodiolus childressi . Two other species were encountered in 

isolated clumps, Tamu fisheri and Idas macdonaldi. T. fisheri has since been found to be 

sulfide-utilizing and associated with tubeworm clumps. The rare I. macdonaldi is more 

problematic, its associations are not clear, and it lacks the hypertrophied gills of other 

seep and vent-associated mussels. While no major shifts in the species composition of 

mat-forming mussels were encountered on the slope above 1000 m. Deeper sites in 

Alaminos canyon and the west Florida escarpment were dominated by combinations of 

Bathymodiolus brooksi and B. heckeri. Where and why the species transition takes place 

is unknown. 

Effective sampling of tubeworms was developed by Harbor Branch 

Oceanographic Institute (HBOI) and C. Fisher during Chemo-II (Fisher et al . 1997). 

Taxonomic work and studies of associated fauna are still in progress. Preliminary results 

indicates that a Lamellibrachia-like species dominates, often in mixed populations with 

an Escarpia-like species. As with the mussels, species composition varies little between 

sites above 1000 m, but a species shift is found at deeper sites. 

130 
An unexpected result of Chemo-I was that the heterotrophic associates of seeps 

(largely mussel beds) were relatively homogenous site-to-site shallower than 1000 m. 

(Carney 1995). It had be incorrectly assumed that random events would play an 

important role in the colonization of each site by animals from the background . Such 

events would cause each site to have a distinctive suite of consumers. To the contrary the 

consumer component, all sites above 1000 m. was dominated by the same three endemic 

gastropod species and two endemic crustacean species . Non-endemic species were 

present in comparatively lower numbers, but the same non-endemics were at all sites. As 

with mussels and tubeworms, major differences in composition were found were 

compared to the deeper sites (Hecker 1985, Carney 1994). 

It can be easily appreciated that this depth dependence of results is quite 

management relevant . If all seep communities above 1000 m in the northern Gulf are 

fundamentally the same, then large populations with a high degree of dispersion are 

likely . Such a distributed but geneticially-linked population may be better able to recover 

from localized impact. However, these a resilient populations do not occupy the entire 

slope. At some depth on the slope there is species replacement. 

There are at least three possible explanations for the observed patterns. First, seep 

fauna could be much like typical deep-sea organisms and show some degree of species 

change (zonal restrictions) with depth. Second, the individual seep organisms themselves 

might be capable of distribution over the entire slope, but are incapable of successfully 

colonizing deeper seeps due to competitive disadvantages . Third, the depth dependency 

of the result could be an artifact of sampling. Of the many sites that may exist above 1000 

m. only a few have been sampled, and even fewer deeper sites . Therefore, limited 

sampling should be seriously considered . 

Study Methods and Activities 

Since 1989, the CSI seep group has carried out dives of the Johnson Sea-Link 

submersible operated by Harbor Branch Oceanographic Institution. These programs have 

been supported by the National Ocean and Atmospheric Administration (NOAH) 

National Undersea Research Program (NURP), the offshore oil and gas industry, the 

Louisiana Board of Regents Industrial Partnership Program, and MMS. The dive sites 

were selected on the basis of industry-provided high-resolution seismic records giving 

indications of seep conditions . These indications included: 

" medium-to-high relief topography suggestive of massive carbonates aligned with 

fault systems, 

" acoustic transparency or "wipe out zones" indicating gas charged sediments, 

" apparent bubble plumes in the water column. 

Dives focused on 24 lease blocks roughly clustered into three groups . A central series 

spanned 70 m to 700 m (Ship Shoal 286, Green Canyon 18, 53, 140,143, 180, 185, 193, 

232, and 237). A western series spanned 300 to 800 m (Garden Banks 171, 189, 201, 215, 

304, 338, 382, and 427). An eastern-most series targeted a much narrower range, 600 to 

800 m (Mississippi Canyon 709, 843, 885, and 929). 

Review of 84 hours of bottom tape provided a means of assessing the gross 

composition of any chemosynthetic communities present. A serious limitation of such 

131 
tape cataloguing is that these were not intended as systematic surveys. The geometry of 

the area surveyed and the spatial relationships are unknown. It is likely that some fauna 

are counted more than once. There is also an inherent bias towards better image coverage 

of exposed rock surfaces, the primary target of the geological dives. For all these 

limitations, data were treated qualitatively in a manner similar to MacDonald (1995) . As 

seen in the results section, this proved adequate . In addition to tapes from twenty four 

lease blocks, faunal ground truth samples were collected on thirteen dives. These 

samples were collected in a manner similar to the faunal studies of the GERG group 

(Carney 1995) . The manipulator arm of the submersible was used to get one full scoop 

from a representative faunal patch . These scoops targeted only mussel clumps since they 

proved unsuitable for collecting worm clumps. This sample was stowed in the "critter 

gitter' on the sub. On deck, samples were sieved through a 500 ~im mesh and preserved 

in seawater buffered 10% formaldehyde. Back in the lab samples were sorted, counted, 

and archived in 80% ethanol. 

4.2 Markers and Recovery Experiments 

4.2 .1 Introduction 

A modest program of long-term observation of marker rods and recovery cages 

initiated in 1989 was included in the Northern Gulf of Mexico Chemosynthetic 

Ecosystem Study (Chemo I) and reported on through 1993 (Carney 1995) . This report 

provides an opportunity to extend the time line of these observations four additional years 

until 1997. This extension has resulted in four main results to be discussed in more detail 

below. First, recovery from disturbance (denuding the bottom of mussels) is not evident. 

Mussels neither migrate into the disturbed area as adults nor settle as larvae . Second, the 

response to new substrate (rods) was very mixed at a single site. Sometimes adult 

mussels became attached to a rod, but other rods remained bare. Recruitment of juveniles 

was extremely limited. Third, there may be major natural disruptions of the environment, 

a recovery cage at Green canyon 272 was first partially buried by faunal burrowing, and 

then completely displaced by massive hydrate movement. Fourth, (as a practical matter) 

long-term monitoring conflicts with investigations requiring large-scale specimen 

collecting. At all sites the extensive submersible activities of the past decade have 

dislodged and otherwise disrupted deployments . This disturbance casts some doubt upon 

the results of this study. 

The deployment of markers of various types, although an ancillary research task, 

is a first step in determining a high-priority management question about hydrocarbon 

seep communities. What happens when they are disturbed? Presumably research 

sampling is a minor impact compared to the damage that might be done by careless 

drilling operation, but community response to small scale perturbations should increase 

the understanding of these systems. Are the seep communities opportunists capable of 

rapidly colonizing a transient seeping feature, an ecology that would make them largely 

impervious to industrial impact? Or, are they specialists which require narrowly 

restricted combinations of geochemistry and substrate? Such specialization, if true, 

would suggest great sensitivity to perturbation . 

132 
4.22 Methods 

The methods have been previously reported (Carney 1995) but are repeated here 

for completeness. Small marker rods have been deployed since 1987 at all surveyed 

sites as a simple frame of reference. Each rod is 0.5 m long 3/4 inch PVC pipe sanded, 

deglazed, and painted with an epoxy based paint. Three primary color bands (red, blue 

and yellow) 10 cm wide were painted to provide scale in low resolution images and aid in 

determining correct color balance in video images. Rods are marked with the dive 

number upon deployment . The most extensive use was at the brine pool where 9 small 

markers were placed at roughly 2m intervals around the outer edge of the pool. 

Large Marker Rods were made of 3m lengths of 1 .0 inch PVC pipe prepared the 

same as the smaller rods, but painted black and white in 20 cm bands. Within the white 

bands, a coded series of rings were drawn to allow identification of location from a closeup image . There has been only one site marked by these large rods, the Brine Pool. 

Seven large rods were deployed across the long axis of the pool. Pole 2596 was laid 

horizontally across the mussel mat at the northern end of the pool on Sept. 13, 1989. On 

following dives, a rod was placed on the mat at the southern brine overflow end. The 

inner edge of the mat was marked near these horizontal rods by rods pushed into the 

bottom of the pool. These poles were within 20 cm of the inner edge of the mussel mat 

but not touching it . Three additional vertical rods were inserted across the length of the 

pool by placement in the bottom. A rod marked "B" was inserted approximately 2 meters 

from the northern end and "C" placed at the southern end. The third 3m long rod, "A", 

sank from sight when placed in the center of the pool. 

In 1991, "recovery cages" were placed in areas stripped bare by massive mussel 

collecting in order to observe and quantify any subsequent recolonization . These 

collections typically removed more than 100 animals from an area of approximately 0.25 

m2. Rectangular recovery cages were constructed of 1/2 inch PVC water pipe. Fifty 

centimeter lengths were used to make 0.25 m2 top and bottom sections, and the remaining 

sides constructed of 20 cm lengths. Corners were fastened with three-way right angle 

joints and commercial PVC pipe adhesive. The corners were drilled to allow for flooding 

of cavities . Half the interior of the cage was enclosed in 3 .5 cm stretch mesh plastic fruit 

tree bird netting. The string of the netting is less than l mm in diameter, is easy to see 

through, and its black color limits obscuring of a video image. Nylon line was stretched 

across the diagonal of the cage, and then netting was secured with tiewraps to these 

diagonal lines and adjacent sides. The 50 cm rods used had been sanded, chemically 

deglazed and painted white, blue, red and yellow with an epoxy based paint. The 10 cm 

long color bands provide visual scale, orientation, and color balance in subsequent image 

analysis . Cages were deployed in conjunction with massive mussel sampling during the 

1991 dive series . Two cages were deployed at Bush Hill on dives JSL-3129 (Sept. 5, 

1991), and JSL-3139 (Sept., 20, 1991) . Single cages were deployed at Green Canyon 

272 on dive JSL-3137 (Sept. 19, 1991), and Green Canyon 234 on dive JSL-3144 (Sept., 

24, 1991). 

133 
4.2 .3 Results to 1998 

The markers at the Brine Pool were last systematically surveyed in 1996 and 

cursorily examined in 1998. Only four of the 12 markers placed at the outer edge of the 

pool could be relocated . It is assumed that the others have been pressed all the way into 

the sediment by the submersible during the extensive sampling at this site . In 1989, seven 

of nine rods were resurveyed showed no growth or retreat of the outer edge of the mat. A 

similar conclusion can be drawn from the resurvey of 1996 and 1998 . All outer edge 

markers have been colonized by a short tubiculous growth, possibly hydroids. No 

colonization by mussels has been seen. 

The large marker rods in the pool had experienced the same knocking about 

which has disturbed the outer edge markers. Most critically, the end markers which were 

separated from the mussel mat by about 20 cm were found in 1994, 1996, and 1998 to be 

touching the mat and lying about 10 cm deeper in the brine. With no other evidence of 

pool rising, it appears that they had been knocked out of position during other 

submersible observations and that the mat edge has been relatively stable between 1989 

and 1996 . Faunistically, the rods retain some unidentified tubiculous organism first noted 

in 1991 . In the 1993 survey, two juvenile mussels, approximately 1 cm in maximum 

dimension were observed on the southern edge rod. This is the only evidence of 

recruitment found in any monitoring of a marker. These were attached at the brine pool 

interface, where a reddish precipitate appears to have formed on the rod. Now that the 

rod is touching the mussel mat, the effects of settlement and migration can no longer be 

separated. 

The rods placed on the mat surface at the southern and northern end continue very 

different courses of development. By 1991, adult mussels were moving on to the 

northern rod, covering about 25% of the surface. In 1993 only the inner 1/2 of the rod 

could be seen. That end was 75% covered with adult mussels, greatly obscuring the rod . 

The rod could not be found in 1996 and is assumed to be lying under the mat. The 

southern rod continues to be moved around by bottom currents. No mussels, either 

juveniles or adults were observed on the rod from 1991to 1996. The mussel cover at this 

end of the pool is limited to discrete clumps . 

Two cages had been deployed in on Bush Hill in 1991, 40 cm apart on a patch of 

flat bottom approximately 3 m. across ringed by exposed carbonates and musseltubeworm clumps. The cages were placed on sediments which had been stripped of 

mussels. One year later both cages had some clumping of adult mussels to the frames, 

but no evidence of juvenile settlement. In Cage One, approximately 15 large (greater 

than 7 cm) mussels occurred as a cluster in the open area of the frame. Approximately 

ten animals of similar size were attached to the frame of the cage on the open side. The 

netted side appeared to be devoid of mussels. The bottom in the open side was colored 

white, suggesting chemical and/or bacterial activity . The bottom on the netted side 

appeared to have no special coloration. The striking feature was that Cage Two had been 

colonized by white Beggiatoa The bacterial film had grown up and over the netted half. 

The sediment under and around it was covered with both white and red Beggiatoa mats. 

Two large mussels were attached to the outer edge of the frame, but none were in the 

open area. At both cages, the crustacean Munidopsis and Alvinocaris were near and/or 

under the cages . 

134 
The condition remained little changed up through 1998 when only a cursory 

survey was made. The Beggiatoa drape covering the second cage had become reduced 

by 1994 and remained restricted to a benthic mat in 1998 . No additional movement of 

mussels on to the frame was seen. The meaning of these observations must be somewhat 

suspect since this site has become a station for tubeworm growth studies. During the 

repeated visits by the submersible, both cages have been accidentally and intentionally 

moved. The site must be considered a chronically disturbed site . 

A single cage was deployed at GC-234 on an area of mud and exposed low relief 

carbonates . The site contained both dense mussel aggregations and mussel-tubeworm 

assemblages. The open section of the cage was whitish due to bacteria or chemical 

activity . Two mussels were attached to the frame in this section in 1991, and an 

additional five added by 1996. Again, there is no evidence of juvenile settlement. 

Alvinocaris, and Munidopsis have used the netted portion as a refuge since the original 

deployment . In 1991 and 1994 six or more of the gastropod Buccinium were found in the 

cage. This observation has not been repeated since. As with the Bush Hill site, the cage 

has been subject to disturbance since deployment . 

The cage deployment at GC-272 exhibited the greatest changes . They were, 

however, due to hydrate movement rather than community change. A single cage was 

originally deployed in denuded area surrounded by additional mussel clumps . Rocks and 

tubeworm bushes surrounded this patch . In 1993, a few adult mussels were noted on the 

frame, but more importantly a large crab burrow (30 cm across) lay within the cage. By 

1994, the cage was sitting atop a low mound approximately 1 m across . In 1996, the cage 

had been completely displaced by exposure of a gas hydrate. The surrounding mussel 

mat was buried under sediment. 

4.2 .4 Discussion 

The long-term observations of the Brine Pool produced two unexpected results 

about mussel beds: first, there appears to be scant new recruitment, and second, there is 

much repositioning of individuals in some parts of the mat. The absence of apparent 

recruitment is the most important result from a management standpoint . When the rods 

were deployed, it was suspected from the structure of the mussel bed that the brine-ocean 

interface provided ideal chemical conditions for mussel colonization . The mussels closest 

to the brine edge were tightly packed and had more small size classes . If true, any new 

surface placed in this environment would be quickly colonized. The meager settling 

observed challenges the prior assumption and raises three questions. First is the new 

substrate ideal (as anticipated) but that new recruitment extremely slow? Alternately, is 

that interface not the ideal environment? Lastly, do the results simply indicate that the 

plastic rod was a poor substitute of the natural substrate required by mussel larvae for 

settling . Due to the importance of determining recolonization rates by settlement, these 

questions warrant resolution in the future . 

The great difference in the horizontal rods at different ends of the pool is quite 

interesting. At the northern end, mussels quickly climbed up on the rod in such large 

numbers that the rod was effectively obscured. This dramatic effect might be due to 

mussels climbing up to escape competition, improve their position in the methane 

gradient, or to escape brine and toxic levels of sulfide. Whatever the reason, it has to be 

135 
assumed that the mussel mat is actually very active with much pushing and shoving as 

animals try to improve their position. Why the southern overflow end is so different is 

hard to explain. Perhaps there is no gradient-based reason to move amount, and the rod 

offers no extra benefit. Or, more simply, there may be less spatial competition in the 

relatively sparse population . 

It can be postulated that when mussels are stripped from an area using the grab of 

the Johnson Sea-Link, that the geochemical environment of the surficial sediments 

undergoes a permanent change. None of the recovery cages experienced a return to predisturbance conditions through adult movement or settlement. Although there was some 

adult migration into the disturbed sites, it was limited. The transitions noted were mussel 

(methane) to Beggiatoa (sulfide) at two locations, and mussel to hydrate mound at one. 

What normally prevents Beggiatoa from enveloping mussel beds as it did the cage at 

Bush Hill? Is it chemical, or can the mussels suppress the bacteria? Resolution of these 

questions is possible, but would require experimentation that measured rates of bacterial 

production and consumption rather than just standing stock. 

4.2 .5 Conclusions Limitations and Recommendation 

Within the limits of an un-replicated experiment employing artificial substrates 

that have been subjected to uncontrolled disturbance, the following can be suggested. 

Disturbed mussel sites do not return to their original conditions within seven 

years. Recruitment by settlement and adult movement appears to be very 

slow. 

The disturbance of denuding may irrevocably alter the geochemistry of the 

sediment-water interface changing the habitat value of that area. 

Mussel beds may be quite dynamic internally with the residents engaged in a 

struggle for a preferred position. If so, this may imply that the conditions 

optimal for community development may be quite narrow, and the animals 

have some ability to seek those optimal conditions . 

More than any other investigation of seep ecology, the long-term monitoring of 

correctly designed and executed experimental disturbances will provide information that 

is of immediate management relevance. In contrast to what should be done, the work 

reported here is just a cursory glance at the problem. It has, however, provided 

interesting starting points for future work and brought to light mundane practical matters. 

Development of a full design is beyond the scope of this study, but some key elements 

can be identified . Experimental manipulation, especially manipulation employing 

exclusion cages, have been an extremely informative approach to marine ecology. With 

their growing popularity, however, it soon became obvious that there were many 

artifacts, confounding effects, and poor control-treatment design (Hairston 1989). Seep 

manipulations must consider these problems even more because poorly understood 

chemical gradients are involved. The factors influenced by a manipulation must be 

known and may include, sensory trigger to settlement, water flow, and position in a 

chemical gradient . 

136 
The practical recommendations are easily arrived at and all relate to the problems 

of submersible-based investigations . 

" Priority - Experimental sites can not be "shared" with other tasks that disturb the 

site . Even when no samples are taken, the damage done by the submersible 

is unacceptable. 

" Innovative Design - It must be realized that the task of site monitoring by 

submersible will be an additional level of disturbance. This may be 

addressed through a design that includes such disturbance or methodology 

that reduces the consequences. 

" Deployed Systems - If detailed examination of an experiment site is seldom 

possible, it is inevitable that the effects of natural events between monitoring 

periods will be confounded with the experimental treatment effects. 

Therefore, it is preferred to maintain some form of continuous surveillance of 

the system. This might entail instrumented packages or moorings. 

4.3 Results of Faunal Study 

4.3 .1 Results of Site Cataloguing 

On the basis of the geological and geochemical studies undertaken by Roberts 

(Roberts and Carney 1997) a simple system of geological categories has been applied to 

all twenty four blocks. This categorization along with simple faunal description is shown 

in table 4.1 . 

Of 24 blocks containing seismic or topographic evidence of seepage, no 

chemosynthetic fauna was detected in five . Of the remaining 19, five had 

chemosynthetic fauna limited to Beggiatoa bacterial mats . The remaining 14 had some 

degree of metazoan community development beyond bacterial mats. In 11, mussels 

clearly predominated and in two tubeworms were clearly dominant. Tubeworm 

dominance (defined as the presence of numerous large bushes) seemed limited to the 

Green Canyon area. Limitations of the study, however, cast doubt on this finding. The 

mussels always appeared to be the common Bathymodiolus childressi. Unfortunately, 

there was insufficient image resolution to determine the species of tubeworms. 

There can be many reasons why seep communities were absent from five sites 

and only bacterial mats observed at five . Most obvious is inadequacy of survey . These 

lease blocks are 3 nautical miles on a side and the targeted geological features extended 

many 100's of meters . It is highly likely that even large clumps of seep organisms could 

have been missed. Discounting inadequate survey, depth seems to be the most obvious 

factor. The five sites with mats only occurred in less than 500 m of water and the five 

with no seep fauna were all shallower than 600 m. It must be stressed that all these sites 

had strong geological evidence of seepage( surface carbonates, subsurface faults, and 

areas of acoustic wipeout), and the presence of the bacterial mats directly confirms the 

presence of sulfide. 

137 
Table 4.1 Geological and Faunal Characteristics of Lease Blocks Studies by the Coastal 

Studies Group. Following MacDonald et al . (1995) fauna were determined 

from video tapes. Abbreviations: M=mussel, V=vestimentifera, B=Beggiatoa, 

and L=lucinid Initials are given in apparent rank of abundance. 

SERIES & BLOCK DEPTH 

Approx 

GEOLOGICAL EVIDENCE of 

SEEPAGE 

Seep Fauna 

CENTRAL 

Ship Shoal 286 70 m Mud Mound None 

Green Canyon 18 200 m Large Carbonate B only 

Green Canyon 53 200 m Complex Site, Mud Mounds, 

Collapse, and Carbonate Mounds 

B only 

Green Canyon 140 290 m Carbonate Mounds B only 

Green Canyon 143 400 m Mud Volcano B only 

Green Canyon 152 500 m Fluid Expulsion L only 

Green Canyon 180 600 m Soft Sediment Mounds None 

Green Canyon 185 600 m Exposed Hydrates V,M,B 

Green Canyon 193 600 m Exposed Hydrates V,M,B 

Green Canyon 237 700 m Ex osed Hydrates & Brines M,B,V 

Green Canyon 232 800 m Exposed Hydrates M,B,V 

Green Canyon 234 800 m Exposed Hydrates M,B,V 

WESTERN 

Garden Banks 171 300 m Carbonate Mounds None 

Garden Banks 189 300 m Massive Dia it None 

Garden Banks 201 400 m Soft Sediment Mounds B only 

Garden Banks 215 500 m Gas Char ed None 

Garden Banks 382 570 m Massive Dia it M,B,V 

Garden Banks 260 600 m Carbonate Mounds M,B,V 

Garden Banks 338 600 m Fluid Expulsion M,B,V 

Garden Banks 304 800 m Complex Site, Mud Volcano, Gas 

vent, Carbonate mounds 

M,B,V 

138 
Table 4 .1 Continued. 

EASTERN 

Mississippi Canyon 600 m Exposed Hydrates M,B,V 

709 

Mississippi Canyon 800 m Exposed Hydrates M,B,V 

843 

Mississippi Canyon 700 m Gas Charged M,B,V 

885 

Mississippi Canyon 600 m Mineral Prone M,B,V 

929 

Even when seep fauna was absent, authigenic carbonates were often present. 

These corresponded well with the deepest reef assemblage was recognized similar by 

Rezak (Rezak et al . 1985) for deep hardgrounds in the Gulf of Mexico. Most of the rock 

surface was bare, low cover was dominated by unidentified encrusting sponges. Large 

fauna was dominated by a gorgonian Callogorgia sp., a scleractinian coral Lophelia 

prolifera, and the antipatherian Leiopathes glaberrima. Cryptic surfaces (undersides of 

rock ledges) were colonized by an unidentified doriid polychaete, and brachiopods . 

When such rock samples were recovered they typically contained a rock-boring fauna 

dominated by cavity filling sponges and an unidentified sipunculid. 

4.3 .2 Results of Mussel Scoops 

The analysis of the 13 samples is presented in table 4.2 . The fauna is remarkably 

similar to that previously reported at the GERG-studied primary sites. There is no 

indication of depth or geographic trends . The sole chemosynthetic organism was the seep 

mussel Bathymodiolus childressi . The gastropod fraction of the assemblage was 

dominated by Bathynerita naticoidea, Provanna sculpta, and Cataegis meroglypta. The 

crustacean fraction was dominated by Alvinocaris stactophilia and Munidopsis sp. There 

were only two hints of any significant differences found. In a sample from Mississippi 

Canyon 709, the dominant gastropod was Cataegis meroglypta that is typically the third 

most abundant elsewhere. Also, a large worm, Methanoaricia dendrobraciata, common 

at Bush Hill and the Brine Pool was not sampled. 

Again, interpretation is limited by the fact that there was very scant sampling. 

The obvious conclusion is that mussel-mat species composition above 1000 m across the 

northern Gulf is monotonous. In this analysis there was no appreciable evidence of 

founder effects or localized species groupings. The dominance of C. meroglypta at one 

site is puzzling, but the seep snails have been observed to aggregate and disperse . Our 

sampling may have happened to sample an aggregation. The absence of the 

Methanoaricia dendrobraciata may simply reflect the fact that most samples were taken 

from exposed rocks. At the Brine Pool and Bush Hill the dense worm populations are 

associated with a highly organic ooze directly under the mussel beds. 

139 
4.3 .3 Dominant Species in the Upper Slope Seep Assemblage 

Having established that a common set of species dominate upper-slope seeps, this 

fauna can be more formally defined and the functionality of the component species 

considered . The better studied mussel assemblage is predominantly a methanotrophic, 

bathymodiolid, bed-forming species inhabited by a suite of three browsing gastropods . 

These radula grazers forage extensively and may play a major role in virtually 

eliminating encrusting epifauna. Of roughly equal abundance are two highly mobile 

crustaceans that may be sub-lethal predators. Such predators take small bites of exposed 

mantle tissue . The mussels, the three gastropods and two crustaceans comprise the 

dominant endemic seep species . While their population sizes vary, they are a consistent 

component of the communities showing no succession or founder effect stages . 

Beyond the six endemics, one habitat-forming producer and five habitatexploiting consumers, there is an additional suite of species drawn from the slope fauna. 

These have been termed colonists (Carney 1994). The colonists tend to be larger 

predators and scavengers . The consistent members of this group include a starfish, a 

predatory gastropod, along with several fishes and crustaceans . An additional faunal 

category, vagrant, was used by Carney (1994) following Tunnicliffe (1991,1992), . These 

are large predators and scavengers that seem to exploit the seep environment as transients 

but are not especially abundant in it . This category consists of large crustaceans and 

fishes . In the following sections, all these major associated fauna will be considered . 

Browsing Seep Endemic Gastropods 

There are several species of gastropods associated with the seeps . In approximate 

sequence of dominance the most common species present are Bathynerita naticoidea, 

Provanna sculpta, and Cataegis meroglypta . Together they comprise the endemic 

browsers. 

Bathynerita naticoidea Clark was the most abundant heterotrophic animal 

collected in association with mussel beds and sometimes exceeded even the mussels in 

abundance. It is a radula browser seldom larger than 1 cm in length . Considerable 

information on the natural history was developed by Zande (1994) . Clarke (1989) 

produced the original description based on Bush Hill material ; Waren and Bouchet 

(1993) extended the description based on additional material . The nerites are primarily 

shallow water species. Bathynerita naticoidea seems to be endemic to the upper slope 

seeps since it is only reported from the Gulf and off Barbados (Olu 1996). It has not been 

found at either the Alaminos canyon or the Florida Escarpment sites. A similar fossil 

nerite has been found at Miocene seep sites in Italy (Taviani 1994), but Waren and 

Bouchet point out that a lack of traits in the fossil form makes equating the two species 

problematic . Bathynerita lays small clutches of direct developing eggs in capsules 

attached to any suitable substrate. The shell has been found to support settlement of 

tubeworms and juvenile mussels. 

140 
Table 4.2 . Faunal Counts for Major Taxa Contrasted with Results at Other Sites 

a o 

i 

. ~ a~ 'Y ~, >, ~ ~o ~ 

v 

o 

U ~ ' 

~ 

> 

L 

C1. 

C 

s 

~ 

~ 

~ 

~ 

Y 

~ 

U 

U 

~ C 

~ ti 

~ -1 -) N ~ 

GB-338 JSL-II-2906 1715 7 9 1 0 2 0 0 0 

GB-193 JSL-II-2907 1810 18 37 2 2 2 0 0 0 

GB-426 JSL-I-3567 1850 28 30 2 1 1 1 1 0 

GB-237 JSL-II-2908 1870 45 103 22 5 0 3 1 0 

GB-382 JSL-I-3307 1978 27 30 3 5 0 5 2 0 

GB-383 JSL-I-3566 2000 6 0 0 1 0 0 1 0 

GB-427 JSL-I-3305 2010 37 63 17 4 0 1 0 0 

GB-427 JSL-II-2896 2010 2 1 0 0 0 0 0 0 

GB-152 JSL-I-3123 1476 19 5 0 0 1 0 0 

MC-709 JSL-I-3124 2280 5 I1 1 0 0 0 0 0 

MC-709 JSL-I-3561 2265 42 19 2 23 0 5 1 0 

MC-929 JSL-I-3309 2110 9 27 4 2 3 2 1 0 

MC-929 JSL-I-3311 2110 19 2 2 5 0 2 0 0 

Average 20.31 25.92 431 3,69 0.69 1 .46 0.62 0.0 

Std. Dev. 14 .58 2934 6.92 6.14 1 .03 1 .85 0.65 0.0 

N=13 

CHEMO 

-I Sites 

Average 26.42 37.23 8.38 1 .46 039 2 .54 0.84 11 .51 

Std . Dev. 35.70 62.78 15.83 3 .56 1 .55 3 .77 1 .31 31 .98 

N=61 

`The radula browser, Provanna sculpta Waren and Ponder, may sometimes 

exceed Bathynerita in number. It was new to science, with the type species coming from 

Bush Hill ( Waren and Ponder 1991). Although the genus Provanna has been collected 

away from chemosynthetic communities, its association with these systems has lead to 

the view that it is primarily a seep and vent endemic. Ten or more species exist 

associated with the chemosynthetic systems of the Pacific . P. sculpta seems to be the 

only member of the genus yet found in the Atlantic. The genus has been placed in the 

family Abyssochrysidae, a relict of a largely extinct group (Houbrick 1979). A 

comprehensive monograph of the genus Provanna has not yet been published, but Waren 

and associates have produced a series of papers describing new species from seep and 

141 
vent systems and refining the description of the genus (Waren and Ponder 1991). Being 

small and matching mussel periostricum in color, it is largely unobserved, but very 

numerous. Present at all sites sampled, it is notably rare at the Brine Pool site . The shell 

usually shows deep dissolution pits which are often the settlement site for juvenile 

mussels. Provanna lacks a planktotrophic form, but it is not known if it has a dispersive 

developmental stage or not. 

Cataegis meroglypta is a radular browser up to 2 cm across . It is similar to 

shallow water snails in that its shell is ornamented, retains color (light green) and is 

nacreous . Previously, Cataegis meroglypta McLean and Quinn has been the third most 

abundant gastropod found. It is now obvious that it sometimes becomes dominant. The 

genus was erected for two species of continental slope trochid, C. finkli and C. 

meroglypta that are apparently opportunistic non-seep grazers (McLean and Quinn, 

1989). The former species was found at slope depths associated with seagrass falls, and 

the latter in the upper slope seep systems. Waren and Bouchet (1993) have reviewed 

current information about the species. Since C. meroglypta has not been reported from 

outside of a seep environment, it may be endemic . Larval development is unknown. 

Endemic Sublethal Predatory Crustacea. 

On the whole, the grab sampler of the Johnson Sea-Link is poorly suited for 

collecting small crustaceans capable of quickly swimming away. Therefore, it is 

assumed that this group has been undersampled. Crustacea living in close association 

with mussel mat and tube worm bushes are a common galatheid, Munidopsis sp., a much 

rarer galatheid Eumunida pitta and the shrimp Alvinocaris stactophila. The first and last 

of these comprise the endemic crustaceans. 

Hydrothermal and hydrocarbon chemosynthetic communities often have high 

populations of three caridean shrimp genera, Alvinocaris, Rimicaris, and Chorocaris. 

Since these genera are new to science, the taxonomic position is not well established, 

However, they appear to represent a distinct group with common phylogenetic affinities . 

Originally placed in the family Bresiliidae (Williams and Chace 1982). Subsequently, the 

new family Alvinocarididae was proposed (Christoffersen 1989) to contain these forms. 

All Alvinocarids share a large chela with a finely serrated blade edge well suited for 

snipping small bits of tissue . Two species of Alvinocaris have been found in Gulf of 

Mexico chemosynthetic systems. The hydrocarbon seeps on the upper continental slope 

are populated by A. stactophilia and both known deeper systems are populated by A. 

muricola. A key to the three species of Alvinocaris has been developed by Williams 

(1988) and was the basis of identification of the specimens collected in this study. It is 

especially noteworthy that none of the 42 benthic shrimp reported on the typical Gulf of 

Mexico deep-sea floor are found in the seep community. Although Alvinocaris 

stactophilia appears to have the typical caridean feeding habit of predator/scavenger, one 

member of the Alvinocarididae, Rimicaris exoculata , is specially adapted to feed upon 

epibiotic chemosynthetic bacteria living on its cuticle. This symbiosis involves epibiotic 

bacteria on the mouth parts (Van Dover, et al, 1988) and in the prebranchial chamber 

(Gebruck et al . 1992 ; Segonzac et al . 1993). A general review and detailed examination 

of the feeding of three species of Alvinocarididae at a mid-Atlantic ridge site has been 

given by (Segonzac et al . 1993). 

142 
The abundant Munidopsis found associated with mussel beds remain undescribed. 

It is somewhat larger than the Alvinocaris, being up to 4 cm in body length (exclusive of 

the chelae) . The species has two large forceps-like chelae which can grasp small bits of 

tissue . The genus is widely distributed in the deep-sea and is often a commensal on 

gorgonians . Juvenile mussels less than O.lmm across have been found clinging to the 

hairs on the body . 

Predator and Scavenger Colonists and Vagrants 

The predatory and scavenging feeding group in the seep communities are not 

endemic, but are come from the background fauna. The distinction between colonist and 

vagrant is unavoidably vague. Colonists are found in the background, but reach 

relatively high population levels in the seep area. As such, they are more characteristic of 

the seep. Two species seem to fit this description well, the predatory snail Buccina 

canatae and the predatory seastar Sclerasterias. In order to say that a particular animal is 

a vagrant, it is necessary to know that their abundance on the typical slope is similar to 

that in the seep. In reality, we have little information about population densities in either 

habitat. Seep sites are visited by more than ten fish species and a similar number of large 

crustacea. Some of these may better fit in the colonist category than the vagrant. 

Sclerasterias sp. is a predatory seastar found on the upper continental slope in the 

Atlantic (Clark and Downey 1991). It can be considered a colonist at seep sites in the 

Gulf. Pequegnat did not report any specimens of Sclerasterias, but the NGMCS study 

(Gallaway et al. 1988) did trawl one in the vicinity of a seep site . The specimens 

collected at seep sites most closely resemble S. tanneri, however, the taxonomic traits 

used are complex and hard to distinguish. Sclerasterias is a prominent feature of seep 

communities, but often goes unobserved, being hidden between the mussel shells and in 

the center of tubeworm clumps. It is a stomach evening predator and has been observed 

preying on both mussels and tubeworms. A keystone species regulatory role may be 

suspected. 

Buccina canatae is a predatory neogastropod that can be considered a colonist. 

The genus Buccina is a cosmopolitan complex common on continental slopes . Both 

Pequegnat(1983) and NGMCS (Gallaway et a1 .1988) reported the genus from typical 

background samples . B. canatae has been collected from seep and non-seep 

environments in the Gulf of Mexico and Caribbean (Waren and Bouchet 1993) . Initially 

observed on the sediment surface of clam areas, it appears to forage widely and form 

aggregations . Aggregation may be related to mating . One aggregation collected from a 

clam bed contained 48 individuals. During the 1992 dive series B. canatae were 

conspicuous within mussel beds at Bush Hill . The species was found at all sites. 

Three crab species, Rochina crassa, Trichopeltarion sp. and Nibilia antilocarpa , 

have been found directly in mussel beds. Other large mobile crustacea are conspicuous in 

seep areas but less commonly in direct contact with vent communities. These include the 

decapods Paralomis cubensis, Chaceon quinquedens, C. fenneri, and the giant isopod 

Bathynomus giganteus. All of these are capable of shell crushing with jaws or chelae . 

As there is no reason to think that seep-area populations are especially high, they should 

be considered vagrants . The large fishes are much like the large crabs; it is hard to 

decide if they should be considered as colonists or vagrants . More than ten species of 

143 
fish have been sighted during dives, but only four seem to have a close affinity for the 

vent communities : Eptatretus sp. (hagfish), Synaphobranchus (cutthroat eels), 

Urophycis cirratus (hake), Hoplostethus sp. (orange roughy), and Chaunax suttkusi 

(previously C. pious). 

Conclusion 

While there is definite site-to-site variation in exact species composition, both the 

chemosynthetic species, the endemic consumers, the colonists, and vagrants are the same 

from Viosca Knoll in the east to Garden Banks in the west. Although there is Beggiatoacolonized methane and sulfide seepage shallower, mussel and tubeworm communities are 

not established shallower than 400 m. 

Recommendations on Future Faunal Studies 

There is limited management utility in continuing to survey fauna in the northern 

Gulf less than 1000 m depth. The uniformity of the species composition seems 

adequately established . It is, however, recommended that future studies focus upon the 

three major remaining questions. 

" Depth Patterns Deeper Than 1000 m. -In spite of the uniformity of upper slope 

community structure, deepest slope-base seep sites are faunally distinct. This 

implies that at some unsampled depth there is a transition in species 

composition. Finding that transition depth and describing the nature of the 

change may help define what conditions limit the distribution of these 

communities. Of direct management consequence is the possibility that seeps 

somewhere deeper than 1000 m may require different management strategies. 

" Population Studies I- While the very uniform species composition of the upper 

slope suggest a community capable of dispersion over large distances, this 

conclusion seems in contradiction to what we know about actual dispersive 

capabilities . For example, the very common snail Bathynerita seems to lack a 

dispersive stage. Any future seep studies should give high priority to well 

designed and expertly executed population studies that assess fecundity, 

dispersion, and actual gene flow. 

" Populations Studies II- Although the habitat-forming mussels and tubeworms are 

the most conspicuous component of seep communities, the vagrants and 

colonists comprise a group of special management relevance. As wide 

ranging organisms they are the component which links seeps to the 

background community. As large predators, these animals may be capable of 

regulating seep populations. Future studies should determine the actual 

degree of trophic transfer and the predation pressure exerted on the seep 

fauna by the vagrant species. 

4.4 Causes of Variation in Seep Communities 

In the preceding sections, it has been stressed that the species pool that contributes 

to seep communities remains remarkably similar across the northern Gulf between 400 to 

1000 m. Therefore, the management task of detecting impact is simplified. Two types of 

impact can be anticipated and recognized by simple faunal comparisons. First, gross 

144 
impacts may interrupt the methane/sulfide flow and cause the seep assemblage to go 

locally extinct . Second and more subtle, flow rates and biological interactions may cause 

a dominance shift in the chemosynthetic and heterotrophic components. The persistent 

shift from mussel to bacterial mat seen in the cage experiment might be reflective of such 

an impact . The natural site-to-site dominance shift of the three endemic browsing 

gastropods may also reflect local variation of the geochemical habitat. 

As with any impact study, management's greatest problem will be establishing the 

causal link between an obvious community change (extinction or dominance shift) and 

suspected impacting activity . This will be difficult because we do not know how often 

either type of shift takes place naturally. Determining these "transitions" will be quite 

difficult, with the only practical method being dependent upon the traditional ecological 

approach of trading place for time. In effect, variation among many places is interpreted 

as being due to a common underlying process at many different stages of development. 

In this section, two models of geological and chemical change at seeps are 

considered . Each helps to explain community difference place to place. Both are, 

however, still quite preliminary and conjectural. The first has appeared in the open 

literature (Roberts and Carney 1997) . They second is still under development. 

A Geological Model for Seep Development 

On the basis of evidence accumulated from a variety of sources, Roberts and 

Carney (1997) proposed a model that considers seepage of methane and sulfide as part of 

a larger system of complex slope processes. Ecologically, this model serves only to help 

explain fauna patterns at two extreme seep environments (new seeps without a 

community and old seeps with extensive communities). Most areas of seepage lie in a 

poorly resolved "intermediate group". It is, however, a starting point and warrants 

management attention . Stating the model from the perspective of the seafloor, a series of 

processes give rise to the creation of seepage conduits . These conduits, that allow for the 

persistence of seep communities, must come in many sizes, shapes, and flow rates. 

Accordingly, there are some long-lived seep communities associated with large persistent 

conduit systems, and others that survived only a brief time. Unless the natural range of 

seep community persistence is known, it may be confounded with oil and gas activities . 

Sediment deposition is a critically important habitat-shaping process on the Gulf 

of Mexico continental slope, since the region has received exceptionally high amounts of 

sediment over geological time from the Mississippi and proto-Mississippi River. These 

sources have been active since the Cenozoic (Winker 1982). At the same time that the 

exact points of deposition have been shifting, eustatic sea-level change shifted deposition 

between inner and outer shelf (Pacht et al . 1990). Salt tectonics is a much more recently 

developed field of geology. Its influence is obvious, but much less well understood. 

Ultimately salt migrates in response to compression and density differences with the 

overlying sediment layers . Given these relations with the accumulated sediment, it is not 

surprising that the growth, locations, and orientations location of salt bodies is 

influenced by variations in sedimentation rate (Talbot 1993, Vendeville and Jackson 

1993). 

145 
The regional topography of the northern Gulf is dominated by domes, canyons, 

and basins . This area has more than 100 basins with relief of more than 150 m, 28 

domes, and eight submarine canyons of various size (Bryant et al . 1990; Bouma and 

Bryant 1995). There is a transition on the slope in the effect of salt tectonics. Shallower 

than 2,000 m, basins lie between shallow salt masses, but deeper salt sheets or nappes 

underlie basins . Faults in this region range from deep growth faults thousands of meters 

deep to small compensating faults less than a hundred meters in depth. It is this spectrum 

of faults that provide the conduits for fluids, gases, and sediment slurries . Superimposed 

on regional fault-generated patterns is a broad spectrum of smaller scale topographic 

features probably created by mass movement (slumping, turbidity flows, etc.) . The 

seafloor manifestation of faults combined with mass-movements is a series of features 

associated with seepage ranging from rapid to slow. On the northern Gulf continental 

slope, seep features range from massive mud-flows and mud volcanoes (Neurauter and 

Bryant 1990; Kohl and Roberts 1994 ; Neurauter and Roberts 1994), through gas hydrate 

deposits (Kennicutt et al . 1985), to carbonate buildups (Roberts and Aharon 1994). 

4.4 .1 The Fault Conduit 

In spite of the complexity of the northern Gulf continental slope, the common trait 

of all seepage features is association with a fault that provides the necessary conduit 

(Behrens 1988; Roberts 1995). The slope province in the Gulf is marked by linear seep 

features lying along the surface of a fault (Roberts 1995). The actual mechanics of 

conduit formation and seepage are currently under investigation (Roberts and Nunn 

1995). Unfortunately, it is not yet possible to discuss the size and persistence spectrum 

of conduits and the ecological systems they support, since the controls on frequency of 

fault movements and flux rates are unknown. The consistent presence of natural oil slicks 

on the Gulf's surface suggests that seepage and venting of hydrocarbons is a widespread 

and ongoing process (MacDonald et al. 1993). 

Conduits carrying rapid, high volume discharges may expel fluid muds with or 

without liquid and gas hydrocarbon. Conduits carrying slow low volume discharges are 

the ones typically associated with chemosynthetic communities. In the setting of very 

slow seepage precipitation of carbonates and barite occurs (Roberts and Aharon 1994). 

Most important to the development and persistence of seep communities is the 

observation that some seep features seem to have undergone a geological succession . 

4.5 Classification of Seep Features 

The Roberts and Carney model classifies all seepage areas into one of three 

categories. 

Rapid Venting Mud-prone features 

Vertical migration of gas and fluids through unconsolidated sediments may 

create a slurry-like mixture of sediment, gas, and water that forms conical "mud 

volcanoes" (Hedberg 1974) . Such "volcanoes" and lower relief mud sheets have been 

observed in the Gulf of Mexico (Neurauter and Bryant 1990; Neurauter and Roberts, 

1992, 1994). Roberts and Carney (1997) cite Green Canyon, block 143 as an example of 

such a mud-prone feature. This 450 to 500 m in diameter cone lies in a water depth of 

146 
335 m, and rises to a height of 35m above the surrounding sea floor. Active mud 

volcanoes show no sign of cementation, but dormant ones may (Neurauter and Roberts 

1994) . The fact that these structures reflect conduits into the deep slope sediment has 

been confirmed from Pleistocene and even Miocene foraminifera in the cone's expelled 

sediments (Kohl and Roberts 1994) . 

In every mud volcano so far examined, living chemosynthetic fauna is limited to 

Beggiatoa mats lying on the surface of the mud slurries . Background fauna is also 

absent, and the surface of mud sheets show minimal amounts of lebenspurren . The rapid 

expulsion of liquid and sediment produces a substrate unsuitable to colonization by 

epifauna and infauna. There may be scattered development of vesicomyid and lucinid 

clams peripheral to the unstable sediments . 

Very Slow Venting Mineral Prone Features 

Mineral-prone features are associated with very slow seepage rates and can be 

considered the opposite of mud-prone systems. The flux of fluid mud and hydrocarbons 

to the sea floor at such features has decreased dramatically leaving mineral-rich fluids, 

small amounts of gas, and perhaps traces of crude oil to affect seafloor geology and 

biology . Barite chimneys and crusts precipitate at local discharge sites. These mineralprone systems are typically associated with large salt domes. The top of these domes 

have complex but shallow fault networks truncated by the underlying salt. Seepage is too 

slow to sustain a complex chemosynthetic community, but there is methane discharge 

and carbonate precipitation by methanotrophic bacteria . Faunal communities tend to be 

limited to methanotrophic mussels with only scattered tube worms and Beggiatoa mats 

suggesting low sulfide levels. Green Canyon 140 is cited (Roberts and Carney 1997) as 

an example of a mineral-prone system. Strong evidence that mineral-prone features have 

developed over a long time come from radiometric dating of barite chimneys which range 

from 194,500 to 133,000 years old (Roberts and Aharon 1994) . 

Slow seepage sites have a fauna similar to that of transitional areas but differ in 

spatial distribution (Roberts and Carney 1997). In such sites, hard substrate dominates the 

center and sediments are restricted to the flanks . Therefore, tube worm and mussel beds 

may dominate the centers. Since seepage conduits may be blocked over large areas by 

rock, community development is restricted to relatively small sites within the larger 

rocky region . Rock areas remote from seeps may be populated by typical deep reef 

species of sea fans, corals, and other non-chemosynthetic species. 

Transitional Features Between Rapid and Slow Venting 

According to the Roberts-Carney model, the most extensive development of seep 

communities takes place at conduits which are intermediate between the too extremes of 

mud-prone and mineral-prone. For these communities to thrive there seems to be three 

important needs, methane, sulfide, and hard substrate for attachment. Transitional flux 

rate sites are distinguished by a patchwork of interspersed soft and hard bottoms and can 

be expected to contain a relatively more diverse fauna, due to the heterogeneity of 

conditions . However, communities are divided into distinct patches . Bacterial mats may 

dot the surface of sediment areas which contain lucinids and vesycomiid clams, whereas 

mussels and tube worms share the same rocky areas as the more ubiquitous bacterial 

mats. The Bush Hill (GC 185) site falls into this category and has the most extensive 

147 
development of a chemosynthetic community so far found in the Gulf. Deep reef sea fans 

may be present with other nonseep species, but rock surfaces will tend to be populated by 

chemosynthetic forms. 

Hard substrate is characteristic of all slower venting systems. Sea-floor lithification at seep sites ranges from isolated nodules in sediment to massive structures that 

may take the form of pavement-like slabs or mound-like buildups (Roberts et al . 1992) . 

When methane and/or sulfide are present, these structures form the physical substrate to 

which fauna attach . These are considered authigenic carbonates composed primarily of 

13C-depleted calcite and aragonite produced by microbial oxidation of hydrocarbons 

(Ritger et al . 1987, Paull et al . 1992) . The 13C signature is considered the main evidence 

of the hydrocarbon origin . Slope carbonates from the Gulf display various amounts of 

13C depletion (8~3C = -23 to -SS%o PDB) (Roberts et al . 1992). This range of values is 

largely attributed to the parent source of carbonate carbon, which is interpreted as having 

been derived from microbial degradation of hydrocarbons ranging from crude oil to 

biogenic methane. 

When methane is present and seeping slowly, two special conditions can arise. 

First, the microbial system (Boetius et al . 2000) needed for production of hydrogen 

sulfide develops. Second, gas hydrates may form providing a relatively stable reservoir 

for methane that might mediate fluctuations in the conduit system (Carney 1994). 

Hydrate features may be mounds such as Bush Hill in GC 185, oblate flats (GC 180-181), 

or elongated along a fault line (GC 232-234). Abundant chemosynthetic communities are 

usually associated with combinations of hydrates, hardgrounds and massive authigenic 

carbonate rocks. It is suspected that development of a methane-driven hydrogen sulfide 

seep must require a narrow range of flow rates and duration . Seepage rate must be 

directly related to the delivery system, the complex of fault created conduits . In the GC 

140, GC 184, and GC 185 area. With respect to duration, major seepage may have only 

begun in the Pleistocene (Cook and D'Onfro 1991). At that time a major thrust fault was 

initiated by salt movement. With respect to rates, there are sites which seem to have 

evolved from rapid venting (mud-prone) to slow seepage (mineral-prone). Good 

examples of areas in this evolution are found within GB 338 and GB 382 which overlie a 

subsurface salt ridge. 

4.5 .1 Evidence of Episodic Seepage 

If seepage is episodic, then seep communities can be expected to arise and fail 

naturally. In order to prevent this natural process from being attributed to oil and gas 

operations it is important to understand the process. The Roberts-Carney model accepts 

that much seepage is episodic . The episodic release of fluids and gas from overpressured 

subsurface compartments has been recorded in mineral deposits in the Gulf Coast basin 

(Cathles and Smith 1983 ; Cathles 1990). Sulfide layers in the Winnfield salt dome 

(Ulrich et al . 1990) provide very good evidence. These were created by episodic release 

of reducing waters . Paleomagnetic dating of these sulfides indicates a frequency of 

around 300 yr. (Kyle et al . 1987). These results are compatible with recent numerical 

modeling solutions that suggest that fluid expulsion from geopressured sediments of the 

northern Gulf of Mexico occurs in short-lived events (Roberts and Nunn 1995). This and 

148 
other studies (Ranganathan and Hanor 1989; Roberts and Nunn 1995) suggest that 

expulsion events create local, transient anomalies in overlying sediments in short periods 

of time, perhaps less than 100 yr. A recent two-dimensional finite element model of a 

SEI (South Eugene Island) 330 area sedimentary basin (Roberts et al . 1996) suggests that 

excess fluid pressures in abnormally pressured sediments would drop to approximately 

half of their original value after about 10,000 yr. of expulsion. They also estimate by 

variable fault permeability simulations, where compaction of fault zone sediments closes 

the fracture network, that fault permeability decreases by one to two orders of magnitude 

within 200 yr. after fluid expulsion begins . 

4.5 .2 Has Faunal Succession Been Seen? 

If there is a geologically-controlled transition in seepage rates over time as 

reservoirs are exhausted and conduits opened and closed, is there a faunal succession? In 

terms of species composition and abundance the answer is a qualified yes. Rapidly 

seeping systems are only successfully colonized by Beggiatoa, indicating that hydrogen 

sulfide is already being produced in these early-state system. The sessile metazoans, 

however, require a stable substrate and can only be successful when lithifaction has had 

time to take place. Ultimately, as the system slows even more and becomes mineralprone, overall population decreases, but species composition remains the same. Since no 

one has actually witnessed the onset of hydrocarbon seeping, we do not know the colonization sequence of the metazoans. Two lines of evidence suggest that once the 

inhibitory nature of rapid venting ceases, colonization can be rapid and no subsequent 

succession takes place. 

Speed of colonization has been confirmed in direct observation of a new Pacific 

hydrothermal site over a 2-yr period . In the hydrothermal case, Lutz et al . (1994) dove in 

April 1991 on a recent eruption site in the east Pacific at about a 2,500 m depth. Thick 

bacterial mats were widespread but conspicuous chemosynthetic metazoans absent . 

Eleven months later (March 1992) the bacterial mats had retreated and one species of 

tube worm with tubes up to 30 cm. long had established colonies . Less than 2 yr. later 

(December 1993), a second tube worm species had colonized the site, reached tube 

lengths in excess of 1 .5m. and become reproductive . In the Gulf case absence of apparent 

succession has been noted for death assemblages at chemosynthetic sites (Powell 1995) 

where slumps had periodically killed communities. There was no sign of species 

succession during reestablishment. These results, however, only address soft bottom 

communities. 

4.5 .3 Limitations of the Model 

At its present level of development, the model's ecological utility is limited to the 

extreme cases . Mud vents lack seep communities since they create an unstable substrate . 

Mineral-prone systems still retain a full suite of seep species, but community 

development is sparse, since the conduit system has become heavily mineralized and 

ineffective. Presumably it can take 1000's of years to make the transition from one state 

to the other. Therefore, such a fluid-to-mineral transitions are unlikely to be confused 

with oil and gas impacts. With additional refinement, however, the model may help 

identify geological structures, isotopic signatures, or mineral suites which could be used 

149 
as shorter-term chronometers for assessing seep system on management-relevant time 

scales . 

Development of a Chemical Gradient Model 

On a finer scale (10's of meters) the species comprising seep communities can 

show dramatic, but inconsistent, segregation. Why don't the thiotrophs (tubeworms, 

Tamu fisheri, and Beggiatoa consistently co-occur in close proximity? Sometimes they 

do ; often they do not. The large-scale Roberts-Carney model provides no clues. 

A simple explanation for the inconsistent spatial segregation of thiotrophs may be 

that there is competitive displacement within the sulfide gradient . In order to examine 

this possibility it is necessary to carefully consider the nature of the gradient . Biogenic 

methane and sulfide are tightly linked by a the complex system of bacterial carbon 

diagenesis . The overall types and sequences of reactions generating these gases are 

considered to be ubiquitous but show great geographic and even greater bathymetric 

variation . In the typical ocean, methane-sulfide system is largely controlled by the influx 

of organic detritus (Janhke et a1 .1982) . Photosynthetic detritus sinks to the sea floor and 

is progressively reduced in route by consumer organisms. Biological demand can be so 

great that oxidizing agents are totally depleted . In the anaerobic sediment, seawaterderived sulfate serves as an electron acceptor and produces sulfides. Deeper, sulfate is 

exhausted, methane is produced by several pathways. This detritus-driven production of 

sulfides and methane is characteristic of shallow marine sediments where detritus input is 

high (Martens and val Klump 1984). Sulfide production in typical (without seepage) 

deep-sea sediments is meager, and methane even lower (Bender and Heggie 1984). 

Deep chemosynthetic communities are not supported directly by detritus-driven 

methane and sulfide production since the rates are too meager. Rather, they are 

dependent upon a system that may be thought of as upside down. Organics in the form of 

liquid petroleum and methane enter the zone for bacterial anaerobic metabolism from the 

bottom. As complex hydrocarbons pass through the zone of bacterial fermentation, some 

additional methane is produced. Above that layer, sulfate reducing bacteria are 

encountered that oxidize methane and other organics with sulfate coming from the 

overlying seawater (Boetius et al . 2000) . At this point both gases needed for thiotrophic 

and methanotrophic organisms become present. Sulfide having been produced from the 

flow of methane. Of the two gases, sulfide is far more reactive and can yield 

substantially more energy to the organisms. Just above the sulfate reducing layer, 

denitrifying bacterial consume the sulfide, and at near the sediment-water interface 

surface aerobic bacteria consume what is left . The less reactive methane diffuses from the 

sediments. 

The feature that distinguishes the Gulf of Mexico's methane driven system is that 

it has so many sources of carbon (biogenic methane, thermogenic methane, and liquid 

hydrocarbons). Of special interest today are the solid hydrates of methane. Hyndman and 

Davis (1992) have proposed that hydrates do not require the supersaturated solutions 

predicted from physical chemistry. Thus, even meager biogenic methane in upward 

migrating pore fluids may "freeze" into concentrated hydrates at the lower boundary of a 

pressure/temperature stability zone for the solid phase. Methane dissolving from the 

layer of hydrate at local points of instability could vent through the sea floor at high 

150 
concentrations . Once in contact with seawater sulfate and a bacterial flora, sulfide would 

be generated by methane oxidation-sulfate reduction and added to the concentrated 

upward flow. 

The manner in which bacteria, tubeworms, and mussels take up hydrogen sulfide 

are quite different. These differences combine with the distinctive morphology of the 

animals to give each a very distinctive geometry of sulfide exploitation . This geometry 

of exploitation may explain the exclusion of some of the biota by the others . It is known 

that the Gulf seep tubeworms, both Lamellibrachia and the Escarpia-like genus, have a 

large portion of their total length in the form of a buried narrow tube. This "root" is 

thinner and much more flexible than the exposed section. Increasingly, it is suspected 

that the "root" is the primary sulfide uptake organ (Julian et al 1999). If there is a dense 

clump of tubeworms, there "roots" can be buried in sulfide-rich sediment layers . Closer 

to the sediment-water interface, oxidation might consume upward migrating sulfide. This 

deep consumption and upper oxidation would preclude both bacteria and mussels from 

obtaining any sulfide. A bacterial mat could, similarly preclude mussels from obtaining 

any sulfide. Methane, however, being relatively non reactive would escape to fuel 

organisms at the surface. 

In effect the model says that the gradients of methane and sulfide are linked in the 

sediment layer where they are created, but then are influenced by different biological 

processes. The particular species composition of the community is controlled by the final 

form of the gradients . Some organisms, notably the tubeworms, have a morphology that 

suggests that they can exploit the gradients to their benefit and to the detriment of 

potential competitors. If this is the case, communities shape, rather than just exploit the 

geochemical gradients. An initial impact upon a community can lead to alteration of the 

gradients that feeds back to impact the community even more severely . 

In terms of the fauna, this competitive gradient utilization model is very well 

suited to testing. It simply requires a carefully designed mapping of the fine scale 

geometry of the community, describing the actual geometry of the regions of methane 

and sulfide uptake . Meaningful measurement of the gradients, however, will be the 

difficult part. Presently, the geochemical studies of the seep system are being conducted 

on the time and space scale convenient to the geochemist. Development of more 

appropriate scales and times will be a major undertaking. 

4.6 Conclusions 

Site-to-site and within-site variation of seep communities in the northern Gulf of 

Mexico between 400-1000 m involves a limited suite of species. This is true for the 

chemosynthetic organisms that contribute the biogenic structure of seep communities and 

to those consumer species that are endemics, colonists, and vagrants . The primary 

contribution of examining additional sites within that depth band has been: (1) 

confirmation of previous conclusions, and (2) refinement in our understanding of the 

upper depth limit of seep community occurrence . The uniformity of component species 

suggests the existence of large, genetically linked, populations that may be able to 

repopulate areas experiencing severe impact. 

151 
While the population structure of seep species may be such that repopulation is 

possible, the limited experiments reported herein detected little or no such recruitment 

over more than 5 years . That some species can disperse has been confirmed; the larvae of 

Lamellibrachia have been cultured (Young et al . 1996). Recruitment is either slow and 

sporadic, or the experiments altered the habitat to such a degree that they were no longer 

suitable for settlement. This latter possibility finds some support in the idea that the 

critical methane and sulfide gradients are shaped by the locally dominant species. 

Removal of one species might shift the gradients and support settlement of a different 

species . This would seem to imply a degree of frailty that may be of management 

concern. 

4.7 General Recommendations 

The seep systems in the Gulf of Mexico comprise one of the most extensively 

studied chemosynthetic communities in the ocean. As such, more is known about the 

distribution of the system and the biology of the component species than anywhere else. 

However, in the course of investigation a certain bias has crept into interpretations . The 

studies have gained considerable understanding of the organisms at four sites at the 

sacrifice of a broader understanding of place-to-place and time-to-time variation . It is the 

contention of this review that a good estimation of these time and place variations is of 

greatest management need. It is this natural variation that will set the limits of detection 

for man-induced impacts. 

It is recommended that future investigations employ a greater geographic range 

focusing narrowly at wide-spread sites on issues of population recruitment and response 

to change. The following studies should be considered . 

Confirmation of Genetic Continuity - Estimation of genetic similarity in the 

chemosynthetic, endemic consumers, colonists, and vagrants should be 

undertaken as a major research task. Such estimation should focus upon sites 

selected to test specific hypotheses about depth ( 500 to 3500 m) and regional 

variation. Due to the relatively few species (15 or fewer would suffice), and 

the large size of the animals, it is possible to do this at the zygote (egg) level. 

This would eliminate confounding effects of post-zygotic selection that often 

limit the utility of such studies . 

Testing of Competitive Gradient Use Model - Microprobe technology should be 

used to map methane and sulfide gradients in the root tangle of tubeworms 

and under bacterial mats. Special attention should be devoted to the 

possibility that organisms intercept sulfide in and below the nitrate reduction 

zone, thus controlling the form of the overlying thiotrophic community. 

Once a means of fine scale mapping has been devised, well-designed 

experimental manipulation may provide strong tests of the model . 

Response to Controlled Impact - A program of well designed and appropriately 

replicated experimental impacts should be initiated. If possible, these could 

be carried out in cooperation with industry activity. Annual response 

sampling by submersible must be augmented with deployed systems. 

Arriving at an appropriate design will be a major intellectual task. 

152 
Colonization of Artificial Seeps - The obverse of impacting a natural system and 

watching what happens is to create an artificial seep with appropriate 

conditions and then predicting what will happen. Such an experiment will 

require development of deployable methane and sulfide generators which 

provide suitable surfaces for settlement. Sulfide generators have been 

deployed and colonized by tubeworms (Carney, in preparation) . 

153 

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