OCS Study 

MMS 2005-038 

 

Coastal Marine Institute 

Characterization of Algal-Invertebrate Mats 

at Offshore Platforms and the Assessment 

of Methods for Artificial Substrate Studies 

Final Report 

Cooperative Agreement

Coastal Marine Institute 

Louisiana State University 

U.S. Department of the Interior

Minerals Management Service 

Gulf of Mexico OCS Region 
U.S. Department of the Interior Cooperative Agreement 

Minerals Management Service Coastal Marine Institute 

Gulf of Mexico OCS Region Louisiana State University 

OCS Study 

 MMS 2005-038 

 

Coastal Marine Institute 

Characterization of Algal-Invertebrate Mats 

at Offshore Platforms and the Assessment 

of Methods for Artificial Substrate Studies 

Final Report 

Author 

R.S. Carney 

June 2005 

Prepared under MMS Contract 

14-35-0001-30660-19932 

by 

Coastal Marine Institute 

Louisiana State University 

Baton Rouge, Louisiana 70803 

Published by 
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: (504) 736-2519 

1-800-200-GULF 

CITATION 

Suggested citation: 

Carney, R.S. 2005. Characterization of Algal-Invertebrate Mats at Offshore Platforms and the Assessment

of Methods for Artificial Substrate Studies: Final Report. U.S. Dept. of the Interior, Minerals 

Management Service, Gulf of Mexico OCS, New Orleans, La. OCS Study MMS 2005-038. 93 pp. 

iii
SUMMARY 

The composition of biofouling communities on three offshore platforms in the Gulf of Mexico was 

examined. A platform in South Timbalier block 54 lay in 22 m of water 40 km from shore. A platform in

Grand Isle block 94 lay in 60 m of water 86 km offshore. A platform in Green Canyon lease block 18 lay

in 219 m at 150 km offshore near the edge of the continental shelf. The three platforms had been the site 

of previous fisheries-related investigations and offered an offshore gradient. Research operations were

carried out from the platforms with Exxon and Mobil corporations hosting and providing logistical 

support. Field sampling was initiated in November 1995, and completed September 1997. 

Video surveying, high-resolution photography, surface scraping, and settling plates were employed to 

describe the biota and to evaluate the effectiveness of the methods. Combined, the methods showed that 

the inshore ST-54 platform biota conformed to a previously recognized inshore type dominated by

barnacles with overgrowths of algae and hydroids. The more seaward platforms conformed to a 

previously recognized offshore type dominated by a mix of bivalves and larger barnacles overgrown by

sponges, hydroids, and ectoprocts (bryozoans). No evidence could be found of a bluewater assemblage.

Settling plates showed that new crust was forming at a slower rate at the most offshore platform, GC-18. 

A scenario was developed which viewed the biofouling crust as a system in equilibrium between

accretionary growth and crust shedding. Loss of crust is a direct consequence of the vertical orientation 

of platform benthos and is an important factor distinguishing platforms from natural systems. Accretion

of the crust is dependent on the passing ocean water for food and new larval settlement. Biotic 

interactions such as predation, competition, and bioerosion all contribute to crust loss directly or in

concert with wave surge. The ecological scenario of an equilibrium system helps identify high priority

research questions. 

Of the methods applied, all provided data and some degree of understanding. Video survey, however, 

proved a poor tool for obtaining quantitative data on species composition, but was very useful for 

planning and site characterization. The higher resolution of photography was better for quantitative data,

the complexity of layered assemblages escaped documentation. Scrape samples were most informative

but lacked consistent quantification. Settling plates produced important rate information, but the demands 

on dive time proved unrealistic given constraints of weather and conflicting platform operations. 

v
ACKNOWLEDGMENTS 

This project required the cooperation and assistance of many people. The Coastal Marine Institute 

program of Minerals Management Service provided funding. Exxon-Mobil provided helicopter

transportation, vessel shipping, and platform accommodations. Drs. Chuck Wilson and David Stanley

arranged this industry cooperation. Dr. Stanley oversaw multiple platform projects. Dr. James Tolan

directed diving. The diving party included J. Tolan, D. Stanley, Mark Miller, Ann Bull, Alan Roy, Joel

Chaky, and Frank Shaughnessy. Dr. Shaughnessy initiated algal studies while in the laboratory of Dr. 

Russ Chapman. Elaine Evers, Debra Waters, and Floyd Demers provided technical support. Converting

images and samples to data was largely carried out by undergraduate student workers: Kevin Kasovitch, 

Hal Palmer, Robin Hawes, Amanda Appelbaum, Lisa Appelbaum, Jonathan Comish, and Dmetry

Chuenko. Dr. Mary Boatman of MMS contributed greatly to the improvement and completion of project 

reporting. 

vii
TABLE OF CONTENTS 

Page 

FIGURES.....................................................................................................................................................xi

TABLES ....................................................................................................................................................xiii

1 INTRODUCTION ..................................................................................................................................1

1.1 A Unique Place and Time ...........................................................................................................1

1.2 A History of Approaches to Marine Fouling Communities........................................................1

1.2.1 Starting with Drag and Deterioration Questions..........................................................1

1.2.2 Influenced by Community Ecology Theory.................................................................2

1.3 Gulf of Mexico Research History ...............................................................................................2

1.4 Gulf of Mexico Research Synthesis............................................................................................4

2 OBJECTIVES AND METHODS ..........................................................................................................5

2.1 Objectives ...................................................................................................................................5

2.2 Initial Design...............................................................................................................................5

2.3 Sites.............................................................................................................................................5

2.4 35-mm Photosurvey ....................................................................................................................7

2.4.1 Photosurvey Methods Background ..............................................................................7

2.4.2 Photographic Equipment and Study Design.................................................................8

2.5 Video Survey ..............................................................................................................................8

2.5.1 Background of Video Survey Methods........................................................................8

2.5.2 Video Equipment and Design.......................................................................................9

2.6 Scrape Sampling .........................................................................................................................9

2.6.1 Background of Scraping Survey Methods..................................................................10

2.6.2 Scraping Method and Design .....................................................................................10

2.7 Settling Plates............................................................................................................................10

2.7.1 Background of Settling Plate Methods.......................................................................10

2.7.2 Settling Plate Method and Design ..............................................................................11

3 SURVEY RESULTS ............................................................................................................................13

3.1 General Success of Field Efforts...............................................................................................13

3.2 Video Survey ............................................................................................................................13

3.3 35-mm Photographic Surveys...................................................................................................16

3.4 Scrape Samples.........................................................................................................................17

3.4.1 Substrate-Forming Fauna Results ..............................................................................20

3.4.2 General Patterns of Carbonate-Depositing Fauna within Platforms ..........................21

3.4.3 Intra-Platform Patterns of Carbonate Cementing Fauna ............................................21

3.4.4 Mobile Fauna Results.................................................................................................24

3.4.5 Results for Biotic Overgrowth ...................................................................................27

3.5 Plates.........................................................................................................................................27

3.6 Specimen Archiving..................................................................................................................30

4 DISCUSSION.......................................................................................................................................33

4.1 Scientific Findings....................................................................................................................33

4.1.1 Biogeography and Platform Biotic Inventory ............................................................33

4.1.2 Depth Relationships ...................................................................................................34

4.1.3 Duration Relationship.................................................................................................34

ix
4.1.4 Production of Epibiotoic Crusts.................................................................................35

4.1.5 Ecological Scenario: a Vertical Benthos....................................................................35

4.1.6 Items for Future Investigation ....................................................................................36

4.2 Utility of Methods.....................................................................................................................37

4.2.1 Image-Based Methodology ........................................................................................37

4.2.2 Biota Sampling Methods............................................................................................37

4.2.3 Settling Plate System..................................................................................................38

4.3 Logistics of Answering and Unanswered Questions ................................................................38

4.3.1 Design and Logistics for a Large-Scale Survey .........................................................39

5 CONCLUSION.....................................................................................................................................41

6 LITERATURE CITED .........................................................................................................................43

APPENDIX A—Checklist of Algae Species............................................................................................A-1 

APPENDIX B—Video Percent Cover Data .............................................................................................B-1

x
FIGURES 

Page 

Figure 2.1. Location of study sites. ...........................................................................................................6

Figure 2.2. Schematic of depth and distance from shore of study platforms. ...........................................7

Figure 3.1. Pie charts of average percent cover determined from digitized Hi-8 video surveys of 

platform legs. ........................................................................................................................16

Figure 3.2. Cluster analysis of all photographs at ST-54 and GI-94 platforms.......................................18

Figure 3.3. Cluster analysis GI-94 photos only.......................................................................................19

Figure 3.4. Cluster analysis of ST-54 photos only ..................................................................................20

Figure 3.5. Cluster analysis of carbonate-forming fauna in scrape samples. ..........................................22

Figure 3.6. Results of cluster analysis ST-54 alone substrate-forming samples. ...................................23

Figure 3.7. Results of cluster analysis GI-94 substrate-forming samples. .............................................23

Figure 3.8. Results of cluster analysis GC-18 substrate-forming samples. ............................................24

Figure 3.9. Correlations among mobile fauna presented as a cluster tree. .............................................25

Figure 3.10. Cluster analysis of mobile fauna...........................................................................................26

Figure 3.11. Cluster analysis for algal and invertebrate overgrowths. ......................................................28

Figure 3.12. Schematic of settling plate deployment and harvest at GI-94. Each bar represents the 

history of a group of 3 plates. ...............................................................................................29

Figure 3.13. Schematic of settling plate deployment and recovery at GC-18..........................................30

Figure 3.14. Settling plate dry weights regression against depth of deployment. .....................................31

xi
TABLES 

Page 

Table 3-1 Timing of Successful Operations at Platforms.....................................................................13

Table 3-2 Correlation Coefficients with Depth and Among Biofouling Categories at South 

Timbalier 54..........................................................................................................................14

Table 3-3 Correlation Coefficients with Depth and Among Biofouling Categories at Grand Isle 94 .15

Table 3-4 Correlation Coefficients with Depth and Among Biofouling Categories at Green 

Canyon 18 .............................................................................................................................15

Table 3-5 Correlation among substrate-forming taxa...........................................................................24

xiii
1 INTRODUCTION 

1.1 A UNIQUE PLACE AND TIME

The “oil patch” of the northwest Gulf of Mexico is a unique marine system in several regards;

possibly the most ecologically important aspect is the extent of introduced structure. From the late 1940’s 

to the present, oil and gas production has resulted in the installation of thousands of hard substrate islands 

from Mobile Bay westward and from coastal embayment to beyond the edge of the continental shelf. 

While it is possible to view this construction as an extension of natural hard bottom, it may be 

ecologically accurate to consider it a whole new habitat, a steel archipelago. It extends from bottom

through the euphotic, tidal, and wave splash zones. Unlike natural seafloor hardgrounds, which can 

accrete shells and tests into bioherms, the predominantly vertical surfaces of platforms shed these same

building components due to waves, predation, and gravity. As a result, the dynamics of platform biota are 

unlike natural systems. 

This manmade system is now at a unique time in its development. The number and area of bottomto-surface platform habitats in the Gulf of Mexico is probably near or at maximum right now (A. 

Pulsipher per. comm.). Many, if not most, new wells in deep water will employ subsea technologies, and 

inshore development will make more efficient use of smaller structures. Older structures will be 

removed, and even if large numbers are cut or toppled to create fish habitat, the most productive upper 

zone will be lost. From now on, the unique platform ecosystem is likely to be in decline. 

The study reported herein was undertaken with two purposes. First on a shorter term, the encrusting 

biota of three platforms west of the Mississippi River were surveyed to compliment extensive fish studies

at those same locations. Second with longer-term intent, the methods and logistics of platform surveying

were being tested with respect to additional investigation. Certain aspects of platform ecology have been 

examined in a series of studies; mostly for fish and least for smaller biota (Beaver et al. 2003; Bedinger 

and Kirby 1981; Bull and Kendall 1994; Bert and Humm 1979; Dokken et al 2000; Fotheringham 1981; 

Gallaway et al 1981a, 1981b; George and Thomas 1979; Gunter and Geyer 1955; Keenan et al. 2003;

Middleditch 1981; Stanley and Scarborough-Bull 2003; Stanley and Wilson 1997; Tolan 2001). Limited

observations have been generalized to characterize the larger region; most notably Gallaway and Lewbel 

(1982). Much fundamental information remains to be found, however, and the validity of previous 

generalizations requires examination. 

1.2 A HISTORY OF APPROACHES TO MARINE FOULING COMMUNITIES

This brief review traces the questions that have driven the larger study of biofouling research since

the 1950’s. Most work has been undertaken for practical reasons of vessel operation and structure 

deterioration. Although seemingly ideal systems for application of ecological theory, few such 

investigations can be found. Where ecological investigation has taken place, fundamental parameters 

such as primary and secondary production remain to be effectively measured due to difficulties of 

methodology.

1.2.1 Starting with Drag and Deterioration Questions 

As with many ocean phenomena that impacted wartime naval operations, biological fouling of ships, 

buoys, and other manmade structures in the marine environment underwent close scrutiny during World 

War II. Biological films thinner than a millimeter were known to increase drag, and fouling was 

implicated as an agent in destructive corrosion. Studies carried out during the war years by a multiinvestigator team at Woods Hole Oceanographic Institution produced a seminal monograph Marine 

Fouling and It’s Prevention (Woods Hole Oceanographic Institution, 1952). The research included biotic 

surveys in all US coastal waters and experimental fouling-plate studies at the University of Miami. 

Although the purpose of the Navy-funded work at Woods Hole/Miami was primarily engineering, 

those studies established an ecological perspective of fouling communities that is still prevalent. Notably,

fouling organisms should be studied as a community. Such fouling communities, lack strong internal 

controls, show little true succession beyond an initial microbial film stage, and are strongly influenced by 

seasonal larval availability. In more contemporary terms, the species structure of biofouling communities 

1
is less controlled by the dynamics of the community, and more controlled by the supply of competent 

larvae in the region. The studies considered the Gulf of Mexico as transitional between temperate and

tropical Atlantic regions. 

By the time of publication of the Woods Hole/Miami studies, the use of paints containing the biocide 

tributyltin was proving an effective means of fouling control. This ushered in two decades of biofouling 

research focusing almost exclusively on antifouling. Some researchers, like Pequegnat (Pequegnat and 

Pequegnat 1968) managed to incorporate ecological observations in antifoulant testing, but community 

studies were otherwise rare. By the 1970s, self-polishing tributyltin paints had been perfected as a 

controlled-release toxic means of reducing fouling for five or more years. Success of these paints caused 

a decline in biofouling studies until tributyltin usage was severely restricted in the 1980s due to pollution

concerns (Evans 1999). Efforts to find acceptable alternative antifouling agents presently support 

considerable biofouling research. Since microbial films play both promoter and inhibitor roles in fouling 

(Mitchell and Kirchman 1984, Maki et al. 1994), they have become the primary focus of research. This

research is heavily biochemical in nature with little community ecology relevance (e.g. Steinberg et al. 

2001). 

1.2.2 Influenced by Community Ecology Theory

The Woods Hole/Miami studies anticipated that biofouling should be studied from a community

perspective at a time when few community concepts had been formalized and quantified. There were few

models available to drive definitive research until the late 1960’s when MacArthur and Wilson (1967)

proposed a general model for island zoogeography and MacArthur (1972) proposed a conceptual basis for 

the general study of distributions. Connell’s work on competing barnacle populations (Connell 1961),

Paine’s work on regulation by predators (Paine 1974), and Dayton’s work on disturbance (Dayton 1971)

all showed the great utility of sessile benthic communities in experimental ecology, although none of that 

work examined artificial biofouling systems. 

Surprisingly, few ecologists in the 60’s and 70’s tried to take advantage of the easy manipulation of 

biofouling communities for experimental purposes. Two studies are noteworthy, Schoener’s use of

settling plates in Puget Sound (Schoener 1974) and Sutherland’s use of a similar system at Beaufort, N.C.

Sutherland was specifically examining the conjecture of the Woods Hole/Miami study that fouling 

communities lacked community control by strong inter-species interactions (Sutherland and Karlson 

1977). The well-designed experiment sought to determine the effect on final community structure exerted

by the presence of dominant sessile organisms by their selective removal. No strong inter-species

interactions were found. It was concluded that seasonal larval availability was a more important

determination of community structure than competition for space by settled forms. Unfortunately, these 

experiments were never repeated in other environments, for longer periods of time, and using larger 

substrates. 

In the past few years there has been resurgence in descriptive biofouling community studies for two 

reasons. First are the reef-like functions of platforms and artificial reefs (Bohnsack and Bannerot 1986, 

Pitcher and Seaman 2000) in the sense of supporting desirable fish populations. The second addresses the 

habitat function for invertebrate species of special interest in both positive and negative senses.

Positively, platforms may afford a refuge habitat for endangered corals (P. Sammarco, per com.).

Negatively, platforms may afford a stepping-stone habitat for invasive pests (Foster and Willan 1979). 

An important conjecture that has arisen recently is that platform communities do actually experience 

strong biotic control arising from species interaction (Bull and Kendall 1994). If this is the case, then

previous conclusions that strong interaction are missing arose incorrectly from: (1) short experimental 

duration, (2) use of small-scale settlement experiments, and (3) narrow taxonomic focus on sessile fauna 

(barnacles, mussels, bryozoa, etc.) rather than the mobile fauna (amphipods, ophiuroids, etc.) occupying

the sessile matrix. 

1.3 GULF OF MEXICO RESEARCH HISTORY

Early platform fouling work in the Gulf of Mexico through the late 1970’s has been reviewed and the 

collective findings combined into an ecological synthesis by Gallaway and Lewbel (1982). Rather than

repeat that work, the review presented here is intended as an update and a consideration of where Gulf

work fits into the larger research picture developed above. 

2
The Gulf of Mexico lies south of the range of shallow mytilid mussels with the important result that

drag on submerged structures caused by biofouling is not a major engineering problem. As such, there

has been relatively little engineering-based research undertaken and even less published. Gunter and

Geyer (1955) completed the first biotic inventory of platforms using deployed metal cylinders at a time 

when oil and gas development was accelerating but still restricted mainly to near-shore areas.

Development continued without much ecological monitoring until passage of the National Environmental

Policy Act in 1969. Three resulting studies in the Gulf of Mexico included fouling communities in multicomponent investigations (Ward et al. 1979; Middleditch 1981; Bedinger and Kirby 1981). 

The Offshore Ecology Investigations (OEI) in Timbalier Bay, Louisiana and adjacent offshore

regions overlapped the current study area (Ward et al. 1979). Most components were intended to test for 

effects in the environment around platforms (Carney 1987), but two addressed platform biota directly. 

Component studies produced a checklist of algal species (Bert and Humm 1979) and a biofouling

community dynamics study (George and Thomas 1979). The algal checklist has been updated in 

Appendix A. Seven platforms were sampled ranging from a coastal bay to outer shelf. Algal occurrence

was noted without respect to depth. The fouling community dynamics study assumed the sampled

communities to be in a stable climax condition rather than a dynamic state of change. 

Platform biofouling continued to be investigated in the context of pollution effects during the

Buccaneer Gas and Oil Field Study off the Texas coast (partially presented in Middleditch 1981). 

Biofouling was studied in a survey context (Fotheringham 1981), and as a subcomponent in a systemsecology approach (Gallaway et al. 1981a). A final whole-system model (Fucik and Show 1981) simulated 

biomass and carbon flux, but not community structure with the fouling component. 

The Central Gulf Platform Study (Bedinger and Kirby 1981) was a comprehensive effects study

conducted off Louisiana. It included a biofouling component (Gallaway et al. 1981b). The results from 

the Buccaneer Gas and Oil Field Study, the Central Gulf Study, and previous results were combined into

an overall synthesis (Gallaway and Lewbel 1982) that remains a definitive today. Of particular 

importance are the models produced by these studies, which provide a guide to future studies that move to

smaller scales to examine inner functions of the biofouling community and also move to larger scales to 

examine northern Gulf ecosystem functions. 

More recently, the systems ecology approach with an emphasis on fish populations has been 

continued in a series of investigations by Dokken’s group at Texas A&M Corpus Christi. A useful 

summary of results can be found in Dokken et al. (2000). Nine artificial and platform reefs lying from 11 

to 194 km offshore in water depths of 30 to 260 m were surveyed for biofouling and/or fish communities 

between 1994 and 1997. Encrusted faunal communities were nondestructively surveyed photographically

at fixed 1.5 m intervals along vertical transects. The imaged area was 0.47 m2

, and encrusted fauna was 

analyzed by classification and counting of 100 random points. Random scraping of 0.25 m2

 areas

provided ground-truth. Analysis and synthesis were considered consistent with Gallaway and Lewbel

(1982). Community structure changed inshore to offshore. As many as four vertical zones were 

recognized. The shallowest being influenced by wave energy and the deepest by the prevalent continental 

shelf turbid layer. 

While most Gulf of Mexico studies have been directed at platform effects or, more recently, reef-like

effects in the northwestern Gulf of Mexico, Pequegnat and Pequegnat (1968) carried out a distinctly

different study in the eastern Gulf. The primary purpose of the study was evaluation of organo-tin 

antifoulants. It did not examine platform biofouling, but looked at introduced substrates on deployments 

near three “Texas Towers” (instrumented structures) located 2, 11, and 25 miles off the coast of Panama 

City, FL. The experimental substrates were plastic floats. Four floats were suspended from cross rungs 

of a ladder-like frame. The frames were suspended on a line at 4, 10, and 17 m below the surface at each

of the 3 sites. The 11 and 25-mile stations had an additional array at 29 m, and the 25 mile station had an

array at 44 m. Floats were deployed and harvested at intervals ranging from two weeks to a year. An

especially interesting aspect of the methods used was harvesting in a manner assuring recovery of small 

mobile fauna. Bags were slipped over each substrate before it was cut loose, trapping all fauna. 

Approximately 680 substrates were analyzed yielding 187 species. The study produced three important 

results: (1) species settlement is closely linked to water-mass bathing the substrates, (2) hydroids and 

gammarid amphipods contribute to very large transient biomass pulses, (3) the fouling species are 

different than those found in the later studies to the west. 

3
1.4 GULF OF MEXICO RESEARCH SYNTHESIS

The most influential biofouling studies conducted in the Gulf of Mexico, in terms of providing an 

overview of community structure and function, have been the biofouling studies at Buccaneer Field

(Gallaway et al.1981a) and Central Gulf Platform Study (Gallaway et al 1981b) conducted by LGL 

Ecological Research Associates. Results were summarized in two readily available reports. These two 

studies along with previous work were developed into an overall synthesis (Gallaway and Lewbel 1982). 

An onshore-offshore change in the biota of 20 studied platforms was recognized as reflecting a

gradient of change (ecotonal) rather than internally homogenous distinct zones. Three general 

assemblage types were recognized on the basis of dominant fauna and indicator species. Especially

obvious was a shift from dominance by barnacles inshore to pelycepods offshore. 

1. Inshore—From shore to mid shelf (0-m to 30-m depth) encrusting fauna was 

dominated by smaller balanoid barnacles overgrown by algae (shallow) and hydroid

(deeper) mats. 

2. Offshore—At midshelf (30-m to 60-m depth) barnacles and pelycepods (primarily 

Isognomon bicolor) were co-dominants at the surface. Deeper, barnacles became

rare and large cemented pelycepods were common (Hyatissa thomasi and Chama

macerophylla). The octocoral Telesto sp. was considered a reliable indicator species

of this assemblage. 

3. Blue Water Platforms—This assemblage was considered characteristic of water 

depths greater than 60-m depths along the outer third of the continental shelf. It was 

not well characterized due to a lack of quantitative samples. Barnacles were reported 

as predominantly lepidaform (stalked), although balanoids were present. Pelycepods

were also dominant. Shelf edge hard bottom forms such as spiny lobster Palinurus

and urchin Euciaris tribuloides were common. 

The more recent surveys off Texas (Dokken et al. 2000) are somewhat difficult to compare with the 

Gallaway-Lewbel biogeographic scheme since the former established faunal patterns from cluster

analysis and the latter was a narrative assessment. In general the Texas platforms represented three biotic 

clusters. All three might fit within Gallaway-Lewbel offshore zone. There was not a simple offshore or 

depth ordering of the clusters. An obvious blue-water zone, in the sense of encountering stalked

barnacles, was not encountered in spite of the considerable distance from land. 

4
2 OBJECTIVES AND METHODS 

2.1 OBJECTIVES

Three well-studied platforms were examined to obtain information about the fouling organisms and to

determine optimal surveying approaches. The specific objectives of the proposed task were threefold. 

1. Describe the biofouling communities at three oil platforms previously investigated

during bioacoustic studies and compare with Gallaway and Lewbel’s (1982) scheme

of inshore-offshore gradient. 

2. Evaluate the effectiveness of surveying methods in order to identify those most 

suitable for wider-area, longer-time studies and be capable of supporting hypothesis

testing. 

3. Develop high quality voucher collections at LSU and the U.S. National Museum of 

Natural History to facilitate taxonomic QA/QC in the future. 

2.2 INITIAL DESIGN

The proposed approach was a modification of diver surveys of subtidal epibiota cover and 

composition (Andrew and Mapstone, 1987) involving fixed vertical /horizontal transects, stratified 

random scraping, and settling plate placement/recovery. Three aspects of biotic pattern were to be 

determined. 

1. Within Platform Variation—Since platforms are structurally complex with numerous 

vertical members and cross braces interacting with the current field, what is the 

variation of the fouling community spatially? 

2. Among Platform Variation—Since the location of a platform determines the 

oceanographic conditions experienced, what is the difference between the platforms 

and how does this difference compare with Gallaway and Lewbel's proposed

zonation? Since it is logistically infeasible to replicate platforms within zones,

platform effects will be confounded with location effects. 

3. Temporal Variation—platforms experience different currents and exposure to coastal 

or oceanic water masses during the year, what happens to the community structure

and to the composition of newly settled (with survival to collection) organisms 

during a year?

The original intent of the study was to visit three platforms as often as three to four times in a year. 

Biota would be surveyed at medium resolution by video, at high resolution with 35mm photography, 

ground truthed by scrape sampling, and settlement studied with settling plates. Within platform variation

would be determined by sampling at fixed depth intervals (1 m, 5 m, 10 m, 20 m, and 30 m) at two

separate legs on each platform. Suction sampling of mobile fauna from the biofouling crust was

attempted on a trial basis, but then pursued in a separate study of fish larvae (Tolan 2001). Unfortunately,

execution of the original design proved impossible due to weather cancellation of field trips, weather 

restrictions on diving once on platforms, and conflicts with platform operation schedules. 

2.3 SITES

Three offshore production platforms were surveyed, Grand Isle 94 (GI-94), South Timbalier 54 (ST54) and Green Canyon 18 (GC-18) (Figure 2.1). These sites were originally selected as an offshore 

transect for fish acoustic surveys (Stanley and Wilson 1996, 1997) and have been included in fish larval 

(Tolan 2001) and fish feeding studies (Keenan et al. 2003). 

5
GC-18

ST-54

GI-94

Figure 2.1. Location of study sites. 

ST-54 lies in only 22 m of water at 28o50.01′N and 90o22.40′W. It was installed in 1956 and is 

operated by Exxon USA. It is an eight-pile production platform 40 km from the nearest land. GI-94 lies 

in 60 m of water at 28o31.33′N and 90o05.52′W. It was installed in 1975 and was operated by Mobil USA

Inc. at the time of the study. It is an eight-pile production platform 86 km from land. GC-18 lies in 219 m 

at 27o56.48′N and 91o02.28′W. It was installed in 1988 and was operated by Mobil USA. It is a six-pile 

production platform near the edge of the continental shelf 150 km from land. 

According to distance offshore and water depth (Figure 2.2), the selected platforms should lie in each

of the three platform assemblage zones established by Gallaway and Lewbel (1982). ST-54 should lie in

coastal assemblage zone, GI-94 in the offshore zone and GC-18 in the blue water zone. The platforms 

are, however, relatively close to the mouth of the Mississippi River and experience a more complex set of

hydrographic conditions than anticipated by Gallaway and Lewbel zones that parallel the coast. The

region enclosing the three survey platforms is subject to considerable annual and shorter-term fluctuation 

in salinity and temperature. Winds and river discharge cause a general cross-shelf progression of a warm

lower-salinity coastal front during the spring and summer months. This front cools, retreats, breaks 

down, and submerges in the winter, allowing high-salinity, warmer oceanic water to encroach landward. 

Superimposed on this general pattern of moving coastal versus oceanic water, low-salinity threads and

lenses of Mississippi discharge transit the region at all times of year. 

Annual surface temperatures at all three platforms range from 20 to 30 degrees Celsius accompanied 

with a salinity variation of 25 to 35.5 ppt. ST-54 experiences this full range but oceanic salinities are 

relatively rare. GC-18 experiences the same range, but coastal salinities are much more rare. GI-94 is 

somewhat intermediate, but experiences conditions more similar to the seaward platform than the

nearshore ST-54. 

Seasonally reduced oxygen (hypoxia) and high turbidity are bottom-associated phenomena that can

be expected to effect biotic colonization. Hypoxia approaching anoxia is a seasonal bottom and nearbottom condition associated with elevated river-driven production in the poorly mixed water landward of

the summer coastal front (Rabalais et al. 1985). ST-54 lies in such shallow water that the platform legs 

below 15 m experience marked seasonal hypoxia. At 60m depth, the 0 to 30-m depth range of this study

for GI-94 lies above major oxygen reduction. Similarly, the 219-m water depth at GC-18 effectively

isolates the zone of study from any bottom hypoxia. High rates of fine sediment influx and bottom 

mixing processes give rise to a semi- permanent bottom boundary layer with a high suspended sediment

load (McGrail and Carnes 1983). It is generally agreed that this turbid or nephloid layer restricts biotic 

colonization within more than 10 m of bottom west of the Mississippi River mouth. East of the river, a 

similar ecologically important turbid layer is absent or more transient. As with hypoxia, the effect on

6
turbidity on biotic colonization is mediated by depth. The study depths at shallow ST-54 lie within the 

turbid layer. The study depths at GI-94 and GC-18 lie above the turbid layer. 

GC-18 GI-94 ST-54

50m

100m

150m

200m

Distance Offshore (Southward from Shore)

Figure 2.2. Schematic of depth and distance from shore of study platforms. 

2.4 35-MM PHOTOSURVEY

Photographic surveying has been a major component of previous platform biofouling studies in the 

Gulf of Mexico since the OEI study. Ideally, it provides a means of rapidly recording images of multiple 

surface areas on a platform from which presence and percent cover data can be obtained. Paired with 

some actual sampling of the biofouling crust to establish species identifications, photosurvey greatly 

increases the area over which distribution patterns can be determined. 

2.4.1 Photosurvey Methods Background 

Seafloor photography did not become a practical survey tool until the development of reliable,

battery-powered xenon flash in 1932 by Dr. Harold Edgerton of MIT (Edgerton 1983). Early seafloor 

surveys were largely qualitative (Vevers 1951, Laughton 1959). The methodology was not widely 

employed initially, since it was not considered adequate for assessing the soft bottom habitats. When

concerns about global reef status increased dramatically in the 1970’s, it was realized that reliable

quantification and rigorous survey designs were badly needed (Loya 1978). Photography was quickly

recognized as a quantitative tool, replacing time-consuming in situ diver assessment with more accurate

point counting of photographic images (Bohnsack 1979). Great concern about statistical rigor in 

hypothesis testing lead to careful consideration of photosurvey sampling design (Dodge et al. 1982). 

Fortunately, equipment was inexpensive since the popularity of SCUBA diving had driven commercial 

development of moderately priced underwater cameras (Nikonos I in 1963) and strobes such as the Ikelite 

brand. 

The primary methods of obtaining data from reef images is point counting, a means of estimating area 

with a long history in several image-based disciplines. Applied to reef studies, it has been strongly 

7
influenced by point counting in petrography (Chayes 1956). The method consists of classifying and 

counting a number of points on an image and then equating the proportion of points in each category 

(species) to image area covered. Determining the optimal (effort versus accuracy) number of points to

count is still an unresolved problem, although geological and ecological applications frequently make use 

of van der Plas and Tobi’s (1965) table to assess adequacy. There used to be a debate as to the best

placement of points. Randomly scattered points were statistically preferable, but time-consuming to

generate when many images needed to be analyzed. Fixed grids were easy to generate, but might impose

bias if the underlying patterns were linear. Today, with computer analysis, generating random point 

overlays is simple and is the primary method. 

2.4.2 Photographic Equipment and Study Design 

Surveys were conducted with Nikonos model V 35-mm cameras equipped with a 35-mm lens, an

Ikelite Ai/n strobe light. Close-up (macro) images were obtained using extension rings and framing

guides. Initially Ikelite 1:3 macro-rings and frames were used, but the system was very susceptible to

leakage. Subsequently, Sea and Sea macro-ring and framing guide was employed with better results. The 

area photographed was 10.5 cm x 7.5 cm. This relatively small area was chosen for three main reasons: 

obtaining a high resolution image, minimizing turbid-water effects, and being roughly the same scale as 

scrape samples and artificial substrate plates. 

The intended survey design was for four photographs to be taken at 5 depth intervals (1 m, 5 m, 10 m, 

20 m, and 30 m) at 2 legs of each of the three study platforms. The four photographs would be taken at 

haphazard positions, two facing outward from the platform, and two facing the interior. Camera flooding, 

and general diving operation problems prevented the full design from being completed. 

2.5 VIDEO SURVEY

Video surveying was incorporated into the study due to the effectiveness of the technique when

employed by the TAMU-CC group submerged structure biotic surveys (Dokken et al. 2000). The appeal 

of the technique lies in the fact that the video record serves two purposes. The imagery provides 

information on platform biota that can be used to provide quantitative data and serves as a highly useful

means of recording general aspects of the surveyed environment. As with photography, it frees the diver

from tedious documentation and allows data production to be carried out once diving is finished. The 

primary limitation of the method arises from the medium to low resolution of video images. 

2.5.1 Background of Video Survey Methods 

Video surveying of the seafloor lagged behind photographic surveying until development of a 

practical recording technology. Commercial recorders were first developed by Ampex in 1956, but were 

far too expensive and fragile for use in field ecology. Cassette systems were not introduced until the 

1970’s. By the early 1980’s, the video home system (VHS) developed and widely licensed by JVC had

become predominant. Electronic miniaturization facilitated development of small consumer-grade

cameras that could be easily housed for underwater use by SCUBA divers. 

The introduction of Hi-8 camcorders in the late 1980’s offered diving scientists a moderate-cost 

means of recording at very good horizontal resolution. Standard protocols for transect video survey have 

been adopted for reef studies by US workers (Rogers et al. 1994). The reef surveys of Aronson (Aronson

et al. 1994) and Carlton and Done (1995) were instrumental in establishing these standards. 

The utility of video camera’s and recorders has, however, always suffered from problems of 

resolution. Video resolution is a confusing topic due to inconsistent use of “horizontal and vertical” and 

intentional misrepresentation in advertising. The National Television Standards Committee (NTSC)

strictly limits vertical resolution, the number of lines counted vertically on a video monitor. That standard

consists of 525 lines scanned in 1/30 of a second. However, only 480 scan lines are actually displayed.

The undisplayed lines contain non-image information. An added degree of complexity arises from fact

that the lines are not displayed in a simple progression (progressive scan). The over-the-air radio 

broadcast bandwidth adopted early in television’s history, and the fading rate of early TV-tube phosphors 

resulted in a flickering image when progressive scan was used. To overcome this limitation, TV images

are interlaced, meaning that odd lines are shown first followed by even lines. In order to be compatible

8
with US video monitors and TV’s all videotape formats have the same NTSC vertical resolution (480 

lines displayed out of 525) and the display is interleaved. 

Horizontal resolution in video refers to the number of vertical lines that can be counted horizontally

using the NTSC standard. Alternately, it can be thought of as the number of distinct dots that can be seen

along each scan line. The number of these dots is much more variable than the NTSC mandated scan

lines. The shadow mask or aperture grate in the display monitor sets the upper limit of horizontal

resolution. 

Interlacing of two fields to create a single frame imposes limits on the crispness of an image if there is

any motion of the object or the camera. At a normal shutter speed of 1/60 of a second (exposure for a 

single field), NTSC video cameras take 2/60 of a second to record a single full frame. The part of the 

image displayed in adjacent scan lines is 1/60 of a second apart in time. Thus, if there is movement, even

relatively slow movement, the displayed object will show shifts between the lines. This appears as a 

blurred margin to the viewer. This interlacing blur due to movement is much less noticeable when 

viewing video than in digitized still images since the eye and brain clean up motion blur very effectively.

Methods of working around interlace blur to create images that are easier to analyze all have 

shortcomings. Most depend upon digitizing only one field (240 scan lines) of the NTSC scan then 

building the missing lines from the information in digitized lines. Depending on the nature of the image 

recorded, these algorithms can induce substantial blur and jaggedness. 

At the time of writing of this report, consumer-grade video equipment is undergoing a transition from 

analog to digital. Most video cameras are now fully digital in the sense of producing a tape of digital

image data. Unfortunately, playback and display are still restrained by the NTSC standards in order to be

compatible with american television sets. The Moving Picture Coding Experts Group (MPEG) has 

defined the digital equivalent of the NTSC image as a 704 x 480 pixel array (MPEG-2). The 704 pixels 

along each scan line, however, are a much higher resolution than analog camera’s are capable of

producing. MPEG-2 is supported by most computer editing and playback software and equipment. High

definition digital video is available with a dramatically improved resolution of 1440 x 1080 pixels, but

equipment that can handle the required data transfer rates without unacceptable levels of image 

compression will not be available at reasonable costs until analog television has been more fully replaced

by digital. 

2.5.2 Video Equipment and Design 

Surveys were to be conducted on the same two legs at each platform where photographs and other

samples were taken. The equipment was a Sony TR-700 Hi8 Video camera housed in a Stingray

underwater housing employing Sunray halogen lights for illumination. SCUBA divers would attempt to 

maintain a fairly constant 0.5 m distance from the leg, surveying vertically between depths of 1, 5, 10, 20, 

and 30 m except at ST-54 where 20 m would be the deepest. At these fixed depths, the diver would video 

around the circumference of the leg. 

Video analysis consisted of playing the tapes on a Sony EVO-9700 video editor. Frames were 

captured for computer analysis using a Data Translation video capture board. Captured images were 

displayed on a DEC alpha workstation. The graphic capabilities of PV-WAVE software were used to

superimpose 100 random points for classification. During the vertical surveying, an image was captured 

approximately every 1 second. During the horizontal survey, 5 adjacent images were captured. The area 

of the image varied from 0.5 to 0.25 m2

, estimated from the images of known objects. Lacking a fixed 

frame of reference, no area correction was applied. 

2.6 SCRAPE SAMPLING

Scraping of biota from platform legs has been an integral part of Gulf of Mexico surveys either as a

primary method or as a ground truth for image-based surveys. Unlike image sampling, it provides 

specimens for identification and has the potential to sample the entire fouling crust rather than just the 

visible surface. 

9
2.6.1 Background of Scraping Survey Methods 

Scraping biota from a platform with a metal tool is a simple process, but one that is very difficult to 

quantify and to assure consistency. Quantification was attempted by George and Thomas (1979) and 

Fotheringham (1981) by sampling a pre-bagged area. The former employed a strapped on grab-like

device, and the latter, hammer and chisel. The consistency problem arises from considerable differences 

in substrate rugosity and strength. 

2.6.2 Scraping Method and Design 

This study employed heavy metal paint scrapers used by hand to chip and pry the biofouling mat from 

platform legs. An attempt was made to scrape a 20 cm x 20 cm area. All freed material was quickly

transferred into 0.5 mm nytex mesh bag. The bags were then clipped to a guideline for surface retrieval. 

Bagged samples were bulk preserved in buffered formalin and shipped ashore for hand sorting of 

specimens down to 1 mm. 

Identification of algae poses special problems associated with the delicate nature of most species and the 

necessity of preparing microscope slides for identification. In preparation for the identification task, 

snorkel surveys were conducted at all three platforms specifically for collection of algae. The collected

material was prepared for slide preparation at sea. The literature was reviewed and an updated species 

checklist prepared (Appendix A). An expert, Dr. Frank Shaunagessy, carried out this preparation. Actual

identification of algae from samples was carried out by general technicians and student workers. 

Identification was limited to genus in the final analysis. 

2.7 SETTLING PLATES

The intent of settling plates was to develop methodology applicable to larger-scale and longer-term 

studies for determination of the composition of the larval pool recruiting to the platforms. Conceptually, 

it may be possible to assess recruitment from the analysis of scraped samples by estimating age of the 

collected biota. This would, however, require extensive investigation of age-growth relationships for a 

great variety of species. When settling plates are used, it is a simple matter to monitor settlement. The 

primary drawback of artificial substrates is that settlement may be different than on the encrusted surfaces 

of fouling communities. For the study at hand, the advantages of plates were seen as outweighing the

disadvantages. 

2.7.1 Background of Settling Plate Methods 

American and European freshwater ecologist pioneered the use of algal settling plates in the 1960’s to

monitor water-quality in polluted waters. Since that time, various types and designs of plate deployment 

have become commonplace in lakes and streams. Settling plates are seeing increased usage for detection

of introduced species, especially the zebra mussel (Marsden and Lansky 2000). Whatever the exact

application, the great appeal of the methods is that they eliminate much of the uncontrolled variation in 

the natural environment and they make quantification simple. 

Marine use of artificial substrates has been highly varied and undertaken for a wide range of 

purposes. Settling plates or experimental modification of platform surfaces have been employed in all 

Gulf studies since Gunter and Geyer 1955. Most marine ecologists dismiss the method as being too far 

from natural systems (i.e. Smith and Rule 2002). Settling plates are, however, seen by some as a 

convenient means of studying settlement processes and larval availability, especially for barnacles (i.e.

Pineda 1994) without the complexity of natural systems. As in the freshwater environment, artificial 

substrates eliminate some of the uncontrolled complexity of the natural environment. They must, 

however, introduce new factors (effects of size, shape, flow, texture) that are poorly known (Butman et al. 

1988). 

The great appeal of settling plates in biofouling research lies in the fact that plates allow 

determination of active recruitment in a very simple manner. Therefore, the method can be easily applied

in large-scale studies. The criticism that plates are artificial systems is less of a concern since platforms 

themselves are artificial. Criticism that plates have unknown scale, hydrodynamic, and substratesettlement effects are all valid. However, these effects can be studied by controlled variation of

10
parameters, or could be kept constant in a large study through standardization. In spite of considerable 

usage in a variety of habitats and a range of taxa, there appears to be no comprehensive review of 

artificial substrate use. Therefore, each new investigation is based upon unpublished prior experience, 

materials availability, and deployment logistics. 

2.7.2 Settling Plate Method and Design 

Plates consisted of a 17 cm by 17 cm square cut from quarter inch gray polyvinyl chloride sheet 

plastic. The size was selected for handling needs and production yield from 4’ x 8’ stock sheets of PVC. 

The surface of the plates were deglazed with deglazing solution to remove manufacturing residues and 

then roughed with a rotary sander. Mounting holes were drilled in two opposing corners. Six plates were 

spaced along a 2” wide nylon cargo ratchet strap so as to be evenly spaced when placed around a platform 

leg. Attachment of plates to the strap was by means of heavy-duty plastic cable ties fed through the plate

holes and holes punched in the belt and reinforced with grommets. Two divers would carry the belt to the 

desired depth, circle the platform leg and tighten the belt in place with the ratchet mechanism. This 

arrangement allowed individual plates to be harvested and replaced. 

Two modifications of an initial plan were made due to practical considerations. First, PVC plates 

were used rather than ceramic. The appeal of ceramic tile is that they could be custom manufactured with

any desired surface texture and mounting holes preformed rather than drilled. During development of a 

deployment system, however, it was determined that breakage and weight during shipment and diver 

installation would be major problems. Comparably lightweight and unbreakable substrates could be made

from plastics. Second, the ratchet belt system proved vulnerable to dislodgement by strong swell. Belts

deployed at 1-m depth were routinely lost, but those deeper survived. Therefore, 1-m belts were replaced 

with one-inch chains. 

Plates were harvested by diver and placed into a bag made of 250-micrometer nylon netting and 

ballistic nylon cloth. The bagged plates were put into 5-gallon pails on the surface. The pail was filled

with 10% formalin solution and shipped by supply boat to the LSU campus. Within two weeks of 

arriving on campus, the formalin was poured off and replaced by 80% ethanol solution. In the lab, plates

were washed over a 250-micrometer screen to catch mobile fauna, photographed to provide a long-term 

record of condition, and the biota enumerated by point counting. Bulk preserved scraping samples will be 

washed over a 250-micrometer screen to remove formaldehyde and hand sorted at 10X magnification. 

Invertebrates and algae will be separated to the lowest possible taxonomic level based on morphology. 

The design followed the overall sampling plan of three platforms, two legs, and depths of 1, 5, 10, 20 m at 

all platforms and 30 m at the deeper two. 

11
3 SURVEY RESULTS 

3.1 GENERAL SUCCESS OF FIELD EFFORTS

A dive team lead by James Tolan visited platforms six times (GC-18), five times (GI-94), and only 

two times (ST-54) between Nov. 1995 and Sept. 1997. All planned components were completed with

some degree of success (Table 3-1). Dependence on diver teams working from three specific platforms,

however, proved far more restrictive than anticipated. Bad weather limited the access to platforms, and

once on platforms, weather limited diving. Conflicts with platform operations also severely limited

access and dive operations. The most important impact was the loss of time series sampling. For the

most part, video, and photography was used only once successfully at the platforms. No successful 

photographs of GC-18 were taken. Scraping was successful at all platforms, but without a time series.

Plates were deployed at all platforms. Interval harvesting and deployment of new plates was carried out 

at GC-18 and GI-94. Unfortunately, no plates were harvested from ST-54 due to platform operations that

would preclude safe diving for the duration of the project. 

Table 3-1 

 

Timing of Successful Operations at Platforms 

Platform Trip Successful activity

Nov. 95 Plates deployed

Plates redeployed 

Grand Isle 94

Apr. 96

Photography 

May 96 Plates redeployed 

Plates redeployed 

Scrapes 

Aug. 96

Video 

May 97 Plate harvest—final

Jan. 96 Plates deployed

Plates redeployed 

Green Canyon 18 

Apr. 96

Video 

May 96 Plates redeployed 

Sept. 96 Plates redeployed 

Scrapes 

Nov. 96 Plates redeployed 

Sept. 97 Plate harvest—final

South Timbalier 54 June 96 Plates deployed

Scrapes 

July 96 Video

Photography

3.2 VIDEO SURVEY

ST-54 and GI-94 were surveyed on two legs as planned. Thirty-seven and 48 images were captured 

from the two respectively. GC-18 was only partially surveyed on a single leg due to camera problems,

diver time constraints, and unanticipated scheduling conflict with platform maintenance activities. Thirty

eight images were captured from GC-18 from 5- to 30-m depths. When video was recorded in the 

vicinity of a fouling panel belt, depth was confidently known. Depths between belts were estimated from 

time. Platform structure complicated consistent videoing around the platform legs. Therefore, position 

(facing in or facing out) was not examined as a factor. 

While the video did provide excellent illustration of the encrusting and fish fauna of the platform, 

quantification proved difficult, especially at ST-54 where visibility was limited. The poor resolution of 

13
the captured image combined with the substrate masking by bushy epifauna made identification very

difficult. The categories used for image classification were 

1. Bare—smooth surface of platform leg clearly visible. 

2. Turf—a catchall term for an encrusted area for which no specific determination could 

be made. 

3. Barnacles—included points falling in and close to the aperture of a barnacle.

Overgrowths frequently masked the extent of barnacle cover. 

4. Standing Sponges—sponges clearly extending from substrate. 

5. Encrusting Sponges—mats identified by red to yellow color. 

6. Bryozoans—white thin mats. 

7. Hydroids—low to bush-like colonial polyps. 

8. Anemones—larger encrusting individual polyps. 

9. Bivalves—shell edges clearly visible. 

10. Algae—thin translucent green to reddish-brown films. 

11. Tunicates—colonies of ovoid bodies. 

12. Bacterial Film—grey film observed only at ST-54. 

Analysis of percent cover based upon point counting of digitized frames sought to determine if the 

three platforms showed vertical patterns within platform and inter-platforms biotic differences. Since

vertical patterns might confound inter-platform patterns, it was examined first by means of simple 

Pearson product moment correlation coefficients (Tables 3-2, 3-3, and 3-4). Data are presented in 

Appendix B. 

Table 3-2 

 

Correlation Coefficients with Depth and Among Biofouling Categories at South Timbalier 54 

ST-54 Depth Bare Turf Barnacle

Bacterial 

Film Sponge2 Hydroid Bryozoa Tunicate Bivalve Algae Anemone

Depth 1.0000

Bare -0.4203 1.0000 -0.1289 0.1604 -0.2056 -0.2071 -0.1602 0.3091

Turf 0.1580 1.0000 -0.5879 -0.2824 0.1126 -0.2971 -0.0533

Barnacle -0.0461 1.0000 0.4336 -0.4811 -0.4759 0.0250

Bacterial 0.7685 1.0000 -0.3348 -0.4708 -0.3285

Sponge 2 -0.0420 1.0000 0.2483 -0.1533

Hydroid -0.3257 1.0000 -0.0036

Bryozoa 

Tunicate 

Bivalve 

Algae -0.5742 0.3091 -0.0533 0.0250 -0.3285 -0.1533 -0.0036 1.0000

Anemone 

n=37 Significant r > 0.3700 α = .90 Bold Faced

14
Table 3-3 

 

Correlation Coefficients with Depth and Among Biofouling Categories at Grand Isle 94

GI-94 Depth Bare Turf Barnacle Sponge1 Sponge2 Hydroid Bryozoa Tunicate Bivalve Algae Anemone

Depth 1.0000

Bare -0.3591 1.0000 -0.3212 0.4316 0.4569 -0.1906 -0.1862 -0.1606 -0.0673 -0.0566 

Turf -0.0245 1.0000 -0.2896 -0.2707 -0.2283 0.2210 -0.2532 -0.2098 0.1951 

Barnacle -0.4278 1.0000 0.0614 -0.1574 -0.1592 -0.2377 -0.1089 -0.0919

Sponge 1 -0.3930 1.0000 -0.1964 -0.2114 -0.1837 -0.0770 -0.0647

Sponge 2 0.3041 1.0000 -0.2749 -0.2631 -0.1259 0.0674

Hydroid -0.0737 1.0000 -0.0733 -0.1982 -0.0958

Bryozoa 0.1975 1.0000 -0.1385 -0.1196

Tunicate 0.2596 1.0000 -0.0440

Bivalve 0.3175 1.0000

Algae

Anemone

n=48 Significant r >0.3300 α = 0.90 Bold Faced 

Table 3-4 

 

Correlation Coefficients with Depth and Among Biofouling Categories at Green Canyon 18 

GC-18 Depth Bare Turf Barnacle Sponge1 Sponge2 Hydroid Bryozoa Tunicate Bivalve Algae Anemone

Depth 1.0000

Bare 0.0763 1.0000 -0.1245 0.2783 -0.1563 -0.0984 0.1631 0.4408 0.3108 -0.1098

Turf -0.1171 1.0000 -0.0727 -0.3556 0.0350 -0.0319 0.0211 0.1540 -0.1229

Barnacle 0.2552 1.0000 -0.0740 0.1264 0.1064 0.1967 -0.1351 -0.2456

Sponge 1 

Sponge 2 0.2976 1.0000 -0.2157 -0.0585 -0.1392 -0.2609 -0.1131

Hydroids 0.5793 1.0000 0.3741 -0.1380 -0.4875 -0.4138

Bryozoa 0.5445 1.0000 -0.0507 -0.3312 -0.2096

Tunicate

Bivalve -0.0059 1.0000 0.3058 -0.1346

Algae -0.6152 1.0000 0.4824

Anemone -0.5955 1.0000

n=38 Significant r > 0.3700 α = 0.90 Bold Faced

At ST-54 vertical zonation is evident from the significant correlations between depth and bare areas, 

bacterial film, and algae. The negative correlation with algae is consistent with decreasing light levels. 

The positive correlation with bacterial film is consistent with near-bottom hypoxia. The negative

correlation with bare patches may reflect more frequent loss of barnacle patches due to greater wave surge 

near the surface. Significant correlations among biotic categories are all negative and may simply reflect 

overgrowth such that turf, sponges, and hydroids obscure barnacles. Near bottom on the platform

bacterial films obscure the small hydroids but not the larger barnacles. 

At GI-94 vertical zonation is evidenced by the significant negative correlations between depth and 

bare patches, barnacles, and stalked sponges (Table 3-3). All three decrease with depth. The only

significant correlations among categories are between bare patches, barnacles ands stalked sponges. This 

may simply reflect the common response to depth. Unexpectedly, stalked sponges and barnacles show no

15
significant correlation. This is mostly likely due to patchy distribution and the fact that the stalked

sponges do not obscure the underlying barnacles. 

Simple vertical zonation of biota at GC-18 is evidenced from correlation analysis (Table 3-4). 

Hydroids and bryozoans are highly variable but increase significantly with depth. Algae and anemones

show the opposite trend, decreasing in percent cover. Of the significant correlations among cover types, 

hydroid-bryozoa and algae-anemone simply reflect the common effects of depth. The positive correlation

between bivalves and bare areas is the only other significant correlation. There are two likely causes, 

both dealing with unmasking of the mollusks. First, areas that appear bare may be due to recent stripping 

of outer encrusting animals, exposing the large cemented bivalves. Second, apparently bare areas may

actually be created by bivalves falling from the substrate in areas of high bivalve populations. 

Vertical zonation was evident from videos at all three platforms. The patterns were primarily 

platform specific with only two suggestions of general patterns. Algae decreased with depth except where

not confidently identified at GI-94. This is consistent with reduced light at depth, but may also represent 

grazing pressure differences. Bare patches decreased with depth except at GC-18. If the presence of

patches in the shallower platforms reflect greater wave-associated current velocities, the most offshore

platform may reflect lower velocities associated with greater bottom depths. 

Statistical assessment of inter-platform similarity is made somewhat problematic due to the presence

of significant but inconsistent vertical differences. An ANOVA partitioned by depth and platform would 

have significant interaction terms and be made unbalanced due to the narrower depth range at the shallow 

ST-54 platform. Therefore, analyses were limited to simpler examination of similarity among platforms 

(Figure 3.1). The video data somewhat resemble the zonation narrative of Gallaway and Lewbel (1982).

Barnacles are most important nearshore at ST-54. Bivalves increased offshore, but were not as visually 

important as sponges. Results at all three platforms showed a limitation of medium-resolution video, the 

large unresolved “turf” comprised from 24% to 33% of the area classified. 

ST-54 

Barnacles Unresolved Turf

Hydroids

34.4% 29.6%

Barnacles Unresolved Turf

GI-94 

6.6% 33.4%

GC-18 

Barnacles Unresolved Turf

Bryozoa

0.9%

11.0% 23.9%

21.7%

Hydroids

 11.7%

Hydroids

35.6%

Algae

2.2%

Algae

7.3%

Bryozoa

 16.7%

Bare

2.1% Bare

1.1%

Bare

2.0%

Bivalves

0.6%

Bivalves

0.5%

Tunicate

5.2% Sponge 2

 20.6%

Sponge 1

 4.3%

Sponge 2

 11.9%

Anemone

 6.5%

Sponge 2

 5.2%

Bacterial Film

 5.0%

Figure 3.1. Pie charts of average percent cover determined from digitized Hi-8 video surveys of platform legs. 

3.3 35-MM PHOTOGRAPHIC SURVEYS

Successful photographic surveys were completed on two legs of ST-54 on a single visit and two legs 

of GI-94 during two visits. Water and light leaks ruined other attempts. No surveys were conducted at 

GC-18 due to early equipment problems and later dive time restrictions. A total of 102 useful images 

were obtained. Visually, the two platforms were extremely different. ST-54 was covered by a dense 

barnacle crust overlain with a dark covering only a few millimeters thick. The covering did not obscure 

the underlying barnacles, although it did make species identification unreliable. Diversity at this inshore 

structure appeared to be low. GI-94 images most often were dominated by extensive overgrowths of

sponge, hydroids, and corals completely obscuring the underlying organisms/structures. Diversity

appeared to be higher at this mid-shelf structure. 

Due to the large number of images and categories (30) of biota observed, cluster analysis was used as

a simple means of assessing intra- and inter-platform patterns. Similarity was calculated as simple

16
Euclidean distance on untransformed counts. Clustering of the similarity matrix was carried out using the 

flexible clustering algorithm.

Given the dramatic visual differences between the darkly overgrown barnacles and ST-54 and the 

bright sponge and hydroid-covered surfaces at GI-94, it was no surprise that cluster analysis of all images 

produced two major clusters (Figure 3.2). All but three ST-54 images clustered together as a relatively

homogenous group. The three exceptions all occurred at 5 m depth and had large areas obscured by

shadows due to rugosity. Most GI-94 images clustered in a single less homogenous cluster with several

isolated small clusters reflecting the greater visual diversity at that platform. Depth, position in versus out 

and cruise had no noticeable patterns. Unequal sampling, however, weakened the ability to detect all

within-platform patterns other than depth. 

Patterns within platforms such as depth, position at a fixed depth, and time (two series at GI-94) were 

also examined by the same cluster analysis. At GI-94, two main clusters were created mainly on the basis

of the percent of sponge cover and unidentifiable area (Figure 3.3). Depth, times, and positions were 

mixed without obvious pattern. ST-54 showed a similar split into two clusters based mostly on the 

percentage of barnacle cover (Figure 3.4). Again depth and position did not have obvious patterns. The 

overall impression of photographic images is that biota is patchy rather than cleanly divided into depth

zones. 

An unanticipated problem with close-up images was the extreme complexity of overgrowths. Most

often, all large fauna found in scrape samples were completely obscured by covering films. 

Unfortunately, the exact identification of the films could not be determined from scrapes. Typically, the 

films were easily destroyed during scraping, and seemed to consist of relatively few layers of algal cells,

other microbes, and hydroid fecal material. For the purpose of analysis, films were classed by color. 

3.4 SCRAPE SAMPLES

Scraping produced 86 samples from all three platforms. One meter depth samples proved hard to get 

due to wave surge. Thirty meter samples proved hard to obtain due to dive time considerations and the

shallow depth of ST-54. Rather than treat all the scarped biota simultaneously, it was considered more

informative to partition the data into three functional groups (Appendix B). 

1. Substrate-Forming—these are the carbonate depositing barnacles and bivalves that 

form the major component of the encrusting mat. 

2. Overgrowths—these are colonial forms such as bryozoa, sponge, algae, hydroids, etc.

generally found as the outermost layer atop substrate-forming species. 

3. Free-living—these are mobile organisms living within and upon the mat including

amphipods, decapods, isopods, ophiuroids, etc. 

Due to the large size and strength of the shelled organisms, they are relatively well sampled by 

scraping. When firmly attached to this shelled substrate, overgrowth organisms are also well sampled.

Some, however, formed semi-attached, neutrally buoyant layers that were broken and scattered into the 

water column during rough scraping. Sampling of free-living forms has to be considered fortuitous with

only specimens trapped in the structure of the mat making it into a sample bag. Due to the distinctiveness

of the categories and unevenness of sampling, each group was analyzed separately. 

17
Predominantly ST-54

Cluster - 

Legs, Depths, & Position

Mingled

Predominantly GI-94

Cluster -

Legs, Depths, & Positions

Mingled

XXXXX XXm 1

Platform

Leg

Depth

Position

 1 = inward

 0 = outward

Sample Key

Photographic Biota

Similarity

ST54N 10m 0

ST54N 05m 1

ST 54N 01m 0

ST54E 10m 0

ST54E 01m 0

ST54E 20m 1

ST54N 20m 0

ST54E 20m 0

ST54E 20m 1

ST54E 05m 0

ST54E 10m 1

ST54N 10m 0

GI94N 01m 0

ST54E 10m 0

ST54N 20m 1

ST54E 05m 0

ST54N 20m 1

ST54N 01m 0

ST54E 01m 1

ST54N 10m 1

ST54N 10m 0

ST54E 05m 1

ST54E 05m 1

ST54E 01m 0

ST54N 01m 1

ST54N 20m 1

ST54E 01m 1

GI94S 05m 0

GI94S 05m 0

ST54E 10m 1

ST54E 20m 0

ST54N 01m 1

GI94S 20m 0

GI94N 20m 0

GI94S 01m 0

GI94S 01m 0

GI94N 20m 1

GI94S 10m 0

ST54N 05m 1

GI94S 10m 1

GI94N 30m 0

GI94N 30m 0

GI94S 20m 1

GI94N 20m 0

GI94N 05m 1

GI94S 10m 1

GI94N 05m 1

GI94N 01m 1

GI94N 20m 1

GI94N 20m 0

GI94S 10m 1

GI94N 10m 0

GI94S 20m 1

GI94N 01m 0

GI94S 30m 1

GI94S 05m 1

GI94S 30m 1

GI94S 10m 1

GI94N 20m 1

GI94N 20m 0

GI94N 20m 1

GI94N 10m 1

GI94S 10m 1

GI94N 10m 0

GI94N 30m 1

GI94S 20m 0

GI94S 30m 0

GI94N 10m 1

GI94S 20m 0

GI94S 20m 1

GI94S 20m 0

GI94N 05m 0

GI94N 05m 1

GI94N 10m 0

GI94N 10m 0

GI94S 05m 1

GI94S 10m 0

GI94N 10m 0

GI94N 10m 0

GI94N 10m 1

GI94N 20m 1

GI94S 30m 1

GI94S 30m 0

GI94S 30m 0

GI94S 30m 0

GI94N 30m 1

ST54N 05m 0

ST54N 05m 0

GI94S 05m 1

GI94S 05m 0

GI94S 05m 0

GI94N 05m 0

GI94N 05m 5

GI94N 01m 1

GI94S 05m 1

GI94N 10m 1

GI94S 30m 1

GI94S 01m 1

GI94S 01m 0

GI94S 01m 1

GI94S 01m 0

GI94S 20m 1

Figure 3.2. Cluster analysis of all photographs at ST-54 and GI-94 platforms. 

18
High Percent Sponge

Cover Cluster - 

No Leg, Depth, or

Position Pattern

Low Percent Sponge

Cover Cluster - 

No Leg, Depth, or

Position Pattern

XXXXXX XXm 1

Platform

Leg

Depth

Position

 1 = inward

V 0 = outward isit

Within GI94 Photographic

Biota Similarity

GI94N 01m 1

GI94N 05M 1

GI94N 10m 1

GI94S 05m 1

GI94N 05m 0

GI94N 05m 1

GI94N 10m 0

GI94N 10m 0

GI94S 05m 1

GI94S 05m 1

GI94S 20m 1

GI94S 10m 0

GI94S 10m 0

GI94S 10m 1

GI94N 10m 0

GI94N 10m 1

GI94N 05m 0

GI94S 05m 0

GI94S 05m 0

GI94S 05m 1

GI94N 01m 0

GI94N 05m 1

GI94S 05m 0

GI94S 05m 0

GI94N 01m 0

GI94N 30m 1

GI94S 20m 1

GI94N 10m 0

GI94N 10m 0

GI94S 10m 1

GI94S 05m 1

GI94S 30m 1

GI94N 10m 1

GI94N 20m 1

GI94S 10m 1

GI94S 30m 1

GI94N 01m 1

GI94N 20m 0

GI94N 20m 1

GI94N 20m 0

GI94N 20m 1

GI94S 10m 1

GI94S 10m 1

GI94N 05m 1

GI94N 30m 0

GI94N 20m 0

GI94S 20m 1

GI94N 30m 0

GI94N 20m 1

GI94S 10m 0

GI94N 10m 1

GI94S 20m 0

GI94S 20m 0

GI94S 30m 0

GI94S 20m 0

GI94S 20m 1

GI94N 20m 0

GI94S 20m 0

GI94S 01m 0

GI94S 01m 0

GI94S 30m 1

GI94N 20m 1

GI94S 30m 1

GI94S 30m 0

GI94S 30m 0

GI94S 30m 0

GI94N 30m 1

GI94S 01m 0

GI94S 01m 1

GI94S 01m 1

GI94S 01m 1

GI94S 01m 0

Figure 3.3. Cluster analysis GI-94 photos only 

19
High Barnacle Cover

Cluster -

No Leg, Depth, or Position

Pattern

Low Barnacle Cover

Cluster - 

No Leg, Depth, or Position

Pattern

Within ST54 

Photographic Biotic

Similarity

ST54N 01m 0

ST54N 10m 0

ST54N 10m 0

ST54N 20m 0

ST54E 05m 0

ST54E 20m 0

ST54E 20m 0

ST54E 20m 1

ST54E 10m 1

ST54E 20m 1

ST54E 01m 0

ST54E 10m 0

ST54N 01m 1

ST54E 10m 1

ST54E 20m 0

ST54N 05m 1

ST54E 10m 0

ST54E 10m 0

ST54N 01m 0

ST54E 01m 1

ST54N 20m 1

ST54N 20m 1

ST54E 01m 1

ST54E 05m 0

ST54E 05m 1

ST54E 05m 1

ST54N 10m 0

ST54N 10m 1

ST54E 05m 1

ST54N 01m 1

ST54E 01m 0

ST54N 05m 1

ST54N 20m 1

ST54N 05m 0

ST54N 05m 0

Figure 3.4. Cluster analysis of ST-54 photos only 

3.4.1 Substrate-Forming Fauna Results 

The epifaunal crust on all three platforms consisted on a site-specific mix of balanoid barnacles, 

cementing bivalves, and byssate bivalves. Gittings et al. (1986) was used as the primary source for 

identification of the barnacles. Cementing and byssate bivalves were identified to genus using the keys of 

Coan et al. (2000) and to species using the descriptions in Abbott (1953). Due to the large number of

small barnacle specimens, only the identity of dominant species were determined at each site and then all

barnacles enumerated without identification. ST-54 was dominated by Balanus reticulatus, B. eburneus

and B. improvisus were present in lower numbers. The larger Megabalanus antillensis formed scattered

clusters. GI-94 had conspicuous large clumps of M. antillensis with much smaller Balanus trigonus

attached. GC-18 had similar clumps of M. antillensis. B. trigonus, and an unidentified balanoid that may

be young M. antillensis.

There is still some taxonomic instability in the barnacles. Gallaway and Lewbel (1982) expressed the 

opinion that B. reticulatus should be correctly identified as B. amphitrite and is the coastal dominant off 

Louisiana. That work identified the conspicuous large barnacles as Megabalanus (Balanus) tintinabulum. 

Gittings et al. (1986), however, implicitly reject the reticulatus-amphitrite confusion, and list B. 

reticulatus as the dominant form. The utility of morphological identification of barnacles in the Gulf of 

Mexico may have reached its limit, and molecular identification may now be the required tool. 

The cementing bivalves were easily identified on the basis of shell morphology and abductor muscle 

number. ST-54 scrape samples yielded only small specimens, possibly in the genus Crassostrea. GI-94 

and GC-18 both had numerous specimens of Chama macerophylla and Lopha frons. Divers observed and 

collected incidental specimens of Spondylus americanus at GC-18, but none were found in the scrape and

settlement samples of the formal design. The thick basal valves of these animals were usually occupied 

by burrowing mussels of the genus Lipthophaga. Two species were present, L. aristata and L. cf. 

20
antillarum, but shell damage during collecting and freeing from the carbonate matrix made identification

past the genus impossible for most specimens. 

The bivalves attached by byssal fibers were easily identified by overall morphology. ST-54 had only 

a few specimens of Isognomen bicolor. This animal was far more common at GI-94 and GC-18 forming 

dense clumps attached to cementing bivalves. Arcidae were also present. Barbatia candida was very rare 

at ST-54, but more common at GI-94 and GC-18. Large specimens of Arca zebra were found only at GI94. Byssal holdfasts were common on cementing bivalves indicating that many arcids may have fallen 

from samples during collecting. A single specimen of Pinctata radiata, the Atlantic pearl oyster was 

found at GI-94. 

The carbonate crust-forming fauna found in this study differs somewhat from the zonation scheme 

proposed by Gallaway and Lewbel (1982). The increased importance of bivalves offshore was 

confirmed. However, the concomitant decrease in barnacle importance is not as great. Even at the GC-18

site, which should fall in the bluewater category, barnacles are still an important component of the 

platform ecosystem.

3.4.2 General Patterns of Carbonate-Depositing Fauna within Platforms 

The distinctiveness of the substrate forming biota at the three platforms is readily apparent from 

cluster analysis (Figure 3.5). Data were normalized prior to analysis to reduce the influence of the 

dominant barnacles on the clustering. Samples taken in close proximity (same depth, same leg, and same 

side of leg) tend to cluster together, but not exclusively so. All except eight samples, each from GI-94 and

GC-18, clustered into three larger groups. The largest cluster contains subgroups consisting primarily of

ST-54 samples. The smallest cluster consisted primarily of GI-94 samples. The intermediate was a

combination of samples from GI-94 and GC-18. Examination of the data showed that the separation of 

the inshore ST-54 samples was due to the preponderance of barnacles at that site and the exclusion of 

cemented bivalves such as Chama and the byssate Arca. The byssate bivalve Isognomon bicolor is 

abundant on the more offshore platforms, but does occur in patches at ST-54; thus the similarity between 

ST-54 and some GI-18 samples. The dissimilarity among some GC-18 and GI-94 samples is largely

associated with the two species of Arcidae more prevalent at GI-94. 

3.4.3 Intra-Platform Patterns of Carbonate Cementing Fauna 

Depth and position patterns at each platform was examined by the same cluster analysis procedure. At 

ST-54, three distinct clusters were found based upon minor contributions to a relatively monotonous 

barnacle cover (Figure 3.6). Ten samples, which had tree oysters in addition to barnacles, formed on

cluster with no consistent depth, leg, or position pattern. Two samples that contained boring mussels in a 

dense barnacle base clustered together, and the remaining 20 samples clustered together containing only 

barnacles. Samples in close proximity were often most similar, but the Isognomon-defined patches 

seemed scattered about the platform structure without definite zonation. It is the presence of tree oyster

patches that resulted in some similarity with GC-18 samples. 

At GI-94 two large clusters were found representing distinct combinations of bivalves and barnacles 

(Figure 3.7). Samples in which one or both species of Arca were relatively abundant formed a cluster of

13 samples. The other cluster was distinguished largely by the absence or rarity of these same species.

Samples in close proximity were often most similar, but patches seemed scattered about the platform 

structure without definite zonation. 

At GC-18 three main patches with one outlier were recognized (Figure 3.8). A large cluster of 15 

samples shared the common trait of containing Arca sp. causing the similarity with GI-94. A. zebra was,

however, missing, causing a dissimilarity. Further subdivision was based largely on the presence or

absence of the boring mussel Lithophaga sp. 

21
ST54E 01m 1

ST54E 05m 0

ST54N 10m 0

ST54E 01m 0

ST54N 05m 1

ST54E 01m 0

ST54N 10m 0

ST54N 05m 1

GC18S 01m 0

ST54E 01m 1

ST54N 01m 1

ST54N 20m 0

ST54E 10m 1

ST54N 20m 0

ST54E 20m 0

ST54E 20m 1

ST54E 20m 1

ST54E 20m 0

ST54N 01m 0

ST54E 05m 1

ST54E 05m 1

ST54E 05m 0

ST54N 01m 1

ST54E 01m 1

ST54N 05m 0

ST54E 10m 0

ST54E 10m 0

GC18N 01m 1

ST54N 05m 0

GC18N 01m 1

GC18S 01m 1

GC18N 01m 0

GC18N 01m 0

GC18N 05m 1

GC18S 05m 1

GC18S 01m 0

GC18S 05m 0

GC18S 10m 1

GC18N 05m 1

GC18S 10m 0

GC18S 01m 1

GC18S 10m 0

GC18S 05m 0

GC18S 20m 0

GI94N 20m 0

GI94N 20m 0

GI94S 20m 1

GC18S 20m 0

GI94S 05m 0

GC18S 30m 0

GC18S 30m 1

GC18S 20m 1

GC18S 30m 1

ST54N 10m 1

ST54N 10m 1

ST54N 20m 1

ST54N 20m 1

GC18N 05m 0

GC18N 05m 0

GC18S 05m 1

GC18S 10m 1

GC18S 20m 1

GI-94N 20m 1

GI-94S 20m 1

GI94N 20m 1

GI94N 10m 0

GI94N 10m 0

GI94S 20m 0

GI94S 10m 0

GI94S 10m 0

GI94S 10m 1

GI94S 10m 1

GI94N 05m 0

GI94S 05m 1

GI94S 05m 0

GI94S 05m 0

GI94N 05m 1

GI94N 05m 1

GI94S 05m 1

GI94N 10m 1

GI94N 10m 1

GI94S 20m 0

Barnacle/Bivalve

Mixed Cluster -

Primarily GC18

Bivalve-Dominated

Cluster -

Primarily GI94

Barnacle-Dominated

Cluster -

Bivalves absent or rare

Primarily ST54

Carbonate Crust Scrape Samples

Figure 3.5. Cluster analysis of carbonate-forming fauna in scrape samples. 

22
Various Barnacle 

Densities, 

Bivalves Absent 

Barnacles with 

Isognomon

Boring Mussels

in Crust

ST54E 01m 0

ST54E 01m 1

ST54E 05m 0

ST54E 05m 1

ST54E 20m 0

ST54E 20m 0

ST54E 20m 1

ST54E 05m 1

ST54N 01m 0

ST54N 20m 0

ST54E 10m 1

ST54N 01m 0

ST54N 01m 1

ST54N 10m 0

ST54E 10m 1

ST54N 05m 0

ST54N 05m 1

ST54E 01m 0

ST54E 10m 0

ST54N 05m 0

ST54E 01m 1

ST54E 05m 0

ST54N 01m 1

ST54N 20m 0

ST54N 05m 1

ST54N 10m 0

ST54N 10m 1

ST54N 10m 1

ST54N 20m 1

ST54N 20m 1

ST54N 20m 1

ST54E 10m 0

Carbonate Crust Within ST-54

Figure 3.6. Results of cluster analysis ST-54 alone substrate-forming samples. 

Bivalve Dominant

Clusters of Arca sp.

Bivale Dominant

Arca rare or absent

GI94N 05m 0

GI94S 05m 0

GI94N 20m 0

GI94N 10m 1

GI94S 20m 0

GI94S 20m 1

GI94N 05m 0

GI94N 05m 1

GI94S 05m 1

GI94S 05m 0

GI94S 10m 1

GI94N 05m 1

GI94S 05m 1

GI94N 10m 0

GI94S 10m 0

GI94N 10m 0

GI94S 20m 0

GI94N 10m 0

GI94S 10m 0

GI94S 10m 1

GI94N 10m 1

GI94N 20m 0

GI94N 20m 0

GI94N 20m 0

Gi94N 20m 0

GI94S 20m 1

Carbonate Crust Within GI94

Figure 3.7. Results of cluster analysis GI-94 substrate-forming samples. 

23
Bivalve Dominated

Arca zebra clusters

Bivalve Dominated

Arca absent

Borers absent

Bivalve Dominated

Arca absent

Borers present

GC18N 01m 0

GC18N 05m 1

GC18S 05m 1

GC18S 10m 1

GC18S 10m 0

GC18N 05m 1

GC18S 01m 1

GC18S10m 0

GC18N 01m 0

GC18S 01m 0

GC18S 05m 0

GC18N 01m 1

GC18S 05m 0

GC18N 01m 1

GC18S 01m 1

GC18S 20m 0

GC18S 20m 0

GC18S 20m 1

GC18S 30m 0

GC18S 30m 0

GC18S 30m 1

GC18S 30m 1

GC18N 05m 0

GC18N 05m 0

GC18S 05m 1

GC18S 10m 1

GC18S 01m 0

GC18S 20m 1

Carbonate Crust Within GC18

Figure 3.8. Results of cluster analysis GC-18 substrate-forming samples. 

The abundance relationship among substrate-forming fauna was examined through calculation of 

product-moment correlation coefficients (Table 3-5). The few large correlations suggested that the fauna 

was not divided into distinct separate assemblages. Significant positive correlations were associated with 

the cementing bivalves Chama pellucida and Lopha frons. The high correlation between these and 

Lithophaga sp reflects the need of a substantial carbonate base for the boring mussel to survive. The

consistently negative, but low correlation, of all species with barnacles is due to near absence of the other

species at the inshore ST-54 site. 

Table 3-5 

 

Correlation among substrate-forming taxa 

N=84 Barnacle Chama Arca

zebra 

Barbatia Lithophaga Isognomon Lopha

Barnacle 1

Chama -0.3367 1

Arca zebra -0.1299 0.3962 1

Barbatia sp -0.2080 0.5501 0.4433 1

Lithophaga -0.2359 0.6348 0.4909 0.4163 1

Isognomon -0.2844 0.3597 -0.0609 0.3329 0.2385 1

Lopha -0.3070 0.6931 0.2096 0.4916 0.4562 0.3516 1

3.4.4 Mobile Fauna Results 

Twenty-four mono-specific or poly-specific categories of mobile fauna were recognized. Amphipods 

were the most numerous and also diverse with eight distinct morpho-species. These were assigned 

numerical codes until specialized research can resolve taxonomic uncertainties. Juvenile and small

decapod crabs were similarly diverse with eight species found and identified with confidence to species or

genus. Six species of ophiuroids were found. Pycnogonids and isopods were represented by single 

species. Polychaetes tended to be small and badly fragmented; all were lumped into a single category and 

rough estimates made as to the number of specimens present. 

24
The existence of consistent mobile fauna assemblages was examined through calculation of amonggroup correlation coefficients followed by cluster analysis. Distinct associations were not found (Figure

3.9). Due to the size of the 24 x 24 correlation matrix, the results are presented as a dendrogram.

Especially noteworthy is the paucity of significant correlations; abundance among species was not closely

related. The largest grouping of six taxa was found across all platforms but tended to be most abundant at 

ST-54. A cluster of five taxa were mostly associated with GC-18. Other taxa were scattered among the 

platforms without much pattern. 

Pycnogonids

Amph Quadrimaera

Amph Ampithoe

Amph Stenothoe

Amph Elasmopus

Polychaetes

Crab Nanoplax

Isopoda

Amph Caprella

Ophiuroid 6 

Amph Ericthonius

Ophiuroid 6

Crab Mithrax

Crab juv.

Ophiuroid 3

Amph Laticorphium

Amph Gammaropsis

Shrimp

Crab Pachygrapsus

Crab Psuedomedaeus

Crab Minippe

Crab Paractea

Cran juv.2

Ophiuroid 2

1.0 0.0 0.5

Correlation

Figure 3.9. Correlations among mobile fauna presented as a cluster tree. 

Inter-platform patterns in mobile fauna was examined by cluster analysis following data 

normalization. Two rather than three clusters were found (Figure 3.10). Both clusters are highly mixed, 

with samples from all platforms and most depths. One was predominantly the inshore ST-54 and the 

most offshore GC-18. The larger contained scrape samples from all platforms. There is very little obvious

order in the distribution of mobile fauna taken as a whole. 

25
Primarily ST-54 with GC-18

Three Platform

Mixture

Mobile Fauna Scrape

Samples

Figure 3.10. Cluster analysis of mobile fauna. 

26
3.4.5 Results for Biotic Overgrowth 

The surfaces of cementing species were almost universally covered with encrusting fauna when

viewed in video and photographs. During scraping, however, much of this overgrowth was dislodged and

broken in such a manner that in preserved samples it was reduced to a mixed debris. This posed a major

problem for quantification. Information about area covered was lost upon collecting, and weight was split

between a fraction still attached to hard substrate and a fraction completely mixed with miscellaneous 

debris. As a result, it was decided to record encrusting fauna only as presences and absence.

Unfortunately, relative abundance information is lost, but artifacts of sampling and sample processing are 

largely eliminated. 

Taxonomic support for identification of encrusting organisms is not well developed, depending upon 

the taxa under consideration. Most algae, especially filamentous film-forming species, required

preparation of slides and high magnification. Shaunagessy’s (Appendix A) updating of the Bert and 

Humm (1979) checklist combined with Schneider and Searle (1991) and Littler and Littler (2000) served 

to identify algae to genus in most cases. Identification of sponges to genus was attempted using Hooper

and Wiedenmayer (1994) and a web-available companion guided (Hooper 2000). A more comprehensive 

volume (Hooper and Van Soest 2003) became available after completion of the identification phase. 

Ectoprocta (bryozoans) were identified with Canu and Bassler (1928); a newer revision and treatment is

needed. 

Thirty-two genera of algae (Appendix A) were identified from scrape samples. These were most

abundant on 1- and 5-m samples and apparently absent at greater depths. Identification of sponges 

proved very difficult, and most material was simply classified as unidentified. The most common sponge 

encountered at GC-18 and GI-94 was a red to pink encrusting form commonly identified as Diplestrella; 

this identification could not be confirmed. The boring sponge Cliona also formed red mats. Brown mats

of Stelleta were common at the ST-54 site. Patches of the blue Halisarca were occasionally encountered 

at the two offshore platforms. Hydrozoans were abundant with Obelia and Turritopsis being predominant 

forms in the thin mat found at ST-54. GI-94 and GC-18 lacked a similar mat, but had numerous colonies 

of Bougainvilla, Eudendrium, Tubularia, and Sertularia. A large number of specimens, especially the 

athecate forms, could not be identified from the bulk-preserved samples. Careful collection with 

relaxation prior to identification will be required. Hard corals were missing from the samples, but a soft

coral identified as Telesto in Gallaway and Lewbell (1982) was common in small colonies. The most 

conspicuous ectoprocts (bryozoans) were low encrusting forms like Membranipora, Aeverillia, and 

Parasmittina. Stalked forms were limited to Bugula. Anemone patches were limited to the genus 

Anthoplura. 

Since data on encrusting forms was limited to presence/absence, inter sample similarities were

calculated with the Jaccard coefficient and clustering carried out via the flexible cluster algorithm. The

results (Figure 3.11) are similar to those obtained from carbonate crust organisms with one important 

exception. As with carbonate forms, ST-54 has a distinct assemblage while GI-94 and GC-18 lump

together. The difference is that shallower samples (1-5 m) at all sites are distinct from deeper. Thus there 

is distinct vertical zonation determined primarily by the light-limited algae. 

3.5 PLATES

The settlement plate study was severely impacted by dive time restrictions and unanticipated platform 

activity. Deployments and recoveries at GI-94 went reasonably well. Renewed drilling and platform

reconfiguration at GC-18 limited access and caused repeated loss of deployments; only partial recovery

was possible. Renewed drilling at ST-54 prevented completion of the project, and none of the 

deployments were recovered. The resulting data allow informative analysis at GI-94 but do not support 

the desired inter-platform comparisons. 

At GI-94 settlement plate installation was initiated on a NW corner leg on 15 Nov. 1995 with 24

plates successfully installed in belts of six at the design depths of 1, 5, 10, 20, and 30 m. Restrictions

delayed installation on a similar set on a SE leg until 13 Feb. 1995. Plates were harvested and replaced on

both legs during visits beginning 23 Apr. and 5 Aug. 1996. All plates were removed 21 May 1997. A 

total of 99 pates were harvested. Multiple constraints on diving impacted the deployment, harvest, and

replacement schedule resulting in unbalanced data with respect to number of samples per leg, at each

depth, and for each duration (Figure 3.12). 

27
1 & 5m

Samples

10 - 30m

GI-94 & GC-18 Samples

Mixed Cluster

1 & 5m

Samples

10 - 20m

Samples

Outliers

ST-54 Primarily

Cluster

GC18S 05m 0

GC18S 05m 1

GC18S 20m 0

GI94N 20m 0

GI94S 10m 0

GI-94S 10m 1

GI94S 10m 0

GI94S 20m 0

GI94S 20m 0

GI94N 10m 0

GI94N 20m 1

GC18S 30m 1

GC18S 20m 0

GC18S 10m 0

GC18S 05m 1

GI94S 10m 1

GC18S 20m 1

GC18S 30m 0

GI94S 20m 1

GI94N 10m 1

GI94N 10m 0

GI94N 20m 0

GI94S 20m 1

GI94N 10m 1

ST54E 20m 1

GC18N 05m 0

GI94N 05m 1

GC18N 05m 1

GI94S 05m 0

ST54E 05m 1

GI94S 05m 1

GI94S 05m 1

GI94N 05m 1

GC18N 05m 1

GC18N 01m 0

GI94N 05m 0

GC18S 01m 0

GC18S 01m 0

GC18N 01m 1

GI94S 05m 0

GC18S 01m 1

GC18N 01m 0

GC18S 01m 1

GC18N 01m 1

GC18N 05m 0

GI94N 05m 0

GC18S 05m 0

ST54N 01m 1

ST54N 05m 0

ST54N 01m 0

ST54E 01m 0

ST54E 05m 0

ST54E 01m 1

ST54N 01m 0

ST54E 01m 0

ST54E 01m 1

ST54E 05m 0

ST54N 05m 0

ST54N 01m 1

ST54E 10m 0

ST54N 05m 0

ST54E 10m 1

ST54E 05m 1

ST54N 05m 1

ST54E 10m 1

ST54E 10m 0

ST54E 20m 0

ST54E 20m 1

ST54N 10m 0

ST54N 20m 0

ST54E 20m 0

ST54N 10m 0

ST54N 10m 1

ST54N 10m 1

ST54N 20m 0

ST54N 20m 1

GC18S 10m 0

GC18S 10m 1

GC18S 20m 1

GC18S 30m 0

GC18S 30m 1

GC18S 10m 1

GC94N 20m 1

ST54N 20m 1

Figure 3.11.Cluster analysis for algal and invertebrate overgrowths. 

28
Jan May Sep Jan May

23 Apr 96 5 Aug 96 21 May 97

Lost

15 Nov 95

NW leg

SE leg

1m

5m

10m

20m

30m

1m

5m

10m

20m

30m

13 Feb 96

GI-94

3 plates

Figure 3.12. Schematic of settling plate deployment and harvest at GI-94. Each bar represents the history

of a group of 3 plates. 

At GC-18 installation was initiated Jan. 1996 on a NW and SE corner leg using belts of six plates at 

1, 5, 10, 20, and 30 m. Both 1 m deployments were missing on 10 April 1996. Replacement with chains 

was delayed until Sept. Harvest, replacement, and repair activity took place during visits on 10 Apr. 

1996, 9 September. 1996, and 18 Nov. 1996. Final harvest was carried out 17 Sept. 1997. During this 

interval, three individual plates were lost at 1m, and entire belts lost at 5 and 10m. The 1m losses may

have been associated with wave surge. The deeper losses appear to have been associated with platform

reconfiguration activity. A total of 66 plates were harvested with only one being lost during diving

operations (Figure 3.13). 

Plate deployments at ST-54 could not be initiated until June 96. Water depth limited deployments to

1, 5, 10, and 20 m. Harvesting was scheduled for May 97, but renewed drilling effectively terminated 

work at that platform. The plates were never recovered. 

All plates were preserved in 10% formalin. Prior to analysis, plates were soaked in water for 48

hours. Plates were photographed for archival purposes. Attached fauna was identified while wet. Plates 

were air dried in a 30o C. drying oven and dry weight determined. Plates at GI-94 were predominantly

covered with Megabalanus antillensis up to 1.5 cm in diameter and Balanus trigonus 3 mm and smaller. 

The most heavily fouled plate had two layers of large barnacles covering it. A bryozoa, Membranipora 

sp. was also common, covering up to 75% of bare plates and over growing barnacles. Plates at GC-18

had similar fauna, but were far more sparsely colonized. Sponge layers were more common, and 4 plates 

had single specimens of the tree oyster Isognomon bicolor attached. 

29
1m

5m

10m

20m

30m

1m

5m

10m

20m

30m

GC-18

NW leg

SE leg

3 plates

18 Nov 96

Figure 3.13. Schematic of settling plate deployment and recovery at GC-18. 

The most informative data obtained from the settling plates were the extent of overall colonization

measured as dry weight (Figure 3.14). At GC-18 and GI-94 the plates at each depth from both legs were

combined for statistical examination. At GI-94 there was an obvious decline in dry weight with depth. A

significant negative correlation with depth was found (r = -0.63) indicating that depth explains only 40%

of the total variance in dry weight. At GC-18 a very similar pattern and negative correlation was also 

found (r = -0.45), but much less variance was associated with depth (~ 20%). Of particular interest are 

the higher dry weight values at GI-94 indicated by the intercept term in regression and the slower

decrease with depth. 

3.6 SPECIMEN ARCHIVING

An archive of preserved specimens has been established at Louisiana State University and is

maintained by Dr. Carney. Identified exemplars are being submitted to the U.S. National Museum of 

Natural History through the department of Invertebrate Zoology. The taxa maintained are listed in the

data tables of Appendix A.

30
GI-94

GC-18

GI-94

GC-18

log(x) = 4.97 - 0.04z log(x) = 3.81 - 0.06z

Logn(dry weight) of Settling Plate

D

e

pth

B

e

ol w

S

urfa

c

e

M

eters

Figure 3.14. Settling plate dry weights regression against depth of deployment. 

31
4 DISCUSSION 

4.1 SCIENTIFIC FINDINGS

The results of the present study are generally consistent with previous works. ST-54 falls into the 

inshore assemblage group with a crust dominated by barnacles. GI-94 and GC-18 fall into the offshore 

assemblage as indicated by abundant bivalves. The outermost GC-18 does not conform to a bluewater

assemblage. As reviewed previously, such an assemblage was not well established by Gallaway and

Lewbel (1982). In spite of a considerable distance offshore surveyed by the Texas A&M University 

Corpus Christi group, a distinct bluewater assemblage has not been found (Dokken et al. 2000). 

4.1.1 Biogeography and Platform Biotic Inventory

The present study along with the OEI investigation represent the easternmost survey of platform biota

while ongoing studies by the Texas A&M Corpus Christi group and the Buccaneer Field study represent 

the westernmost. Similarity of results, allowing for different sampling methods, suggest that there is a 

common suite of carbonate-forming organisms across the region such that there are no major east-west

biogeographic patterns other than the inshore/offshore change. The taxonomy of these species appears to

be stable, although the autecology of the species has been poorly studied. Growth rates, reproduction

timing, etc. are unknown. Assessment of mobile faunal is less complete. Although other reports list 

species names for the very abundant amphipods, there have been no contemporary revisions of the

taxonomy of this extremely diverse group of organisms, and identification beyond genus may be 

questionable. Colonial and film-forming species are also problematic. There may be a common species

pool across the region for algae, but hydroid and sponge taxonomy is too poorly developed to draw such

conclusions. Expert taxonomic examination and possible revision must be conducted for the mobile and

encrusting fauna before resolution of patterns can be made. 

The only work east of the Mississippi has been Pequegnat and Pequegnat’s (1968) settling study.

That study produced a very different species inventory than surveys to the west of the river. 

Traditionally, the transition from heavily sedimented habitat west of the river to lower sedimentation 

habitat eastward has been considered a biogeographic boundary. A species change on offshore structures 

would be consistent with this view. Since scrape samples were not obtained, however, it is difficult to be

confident about comparisons. 

Overgrowing algae, hydroids, sponges, anemones, and corals show a similar strong contrast between

inshore and offshore. Inshore, relatively thin (1 mm-5 mm) coverings of algae and hydroids cover the 

walls of the dense barnacle cover, but do not obscure the balanoids. Offshore, sponges are strongly 

dominant and can completely obscure the underlying barnacles and bivalves. Mobile fauna is dominated 

by amphipods and juvenile ophiuroids. Strong inshore versus offshore patterns were not obvious. These 

populations represent short-term phenomena with recruitment from the plankton. 

This and previous studies have been descriptive and have undertaken no experimentation that can

identify potential causes for the distinct inshore versus offshore zonation of cementing biota. 

Physiological stress brought about by lower salinity and colder winter temperatures inshore are obvious 

possibilities. The great abundance of the tree oyster Isognomon bicolor offshore is, however, hard to

explain. I. bicolor is a mangrove prop root species well adapted to estuarine conditions. The possibility

exists that the distinct inshore/offshore differences reflect competitive outcomes on these artificial

systems different from outcomes on natural substrate.

The picture that emerges from comparison of substrate samples and mobile faunal samples is

consistent with the apparent persistence of the fauna. Cementers showed distinct inshore/offshore 

patterns. Mobile invertebrates showed much less distinct zonation. Substrate formers are immobile

(cemented) or virtually so (byssate). While we do not know the age of these organisms, size alone argues 

that they may be older than the much smaller mobile forms. Spatial pattern of substrate formers probably 

reflects a longer time integral of recruitment and long-term adult survival. Of the mobile fauna,

amphipods are known to show short-term (possibly seasonal) fluctuation in abundance of several orders 

of magnitude (Beaver et al. 2003). As such, the patterns found reflect settlement and survival dynamics 

sampled at unknown stages in progression. 

33
4.1.2 Depth Relationships 

Depth changes have been noted by all authorities. Gallaway and Lewbel (1982) described a species 

and abundance shift, and Dokken et al. (2000) showed distinct vertical zonation in cluster analyses. Depth

shifts found in this study differed among components. Shifts in species were noted in large-scale video

survey, in scrapes of algae-containing overgrowth, and in apparent fouling rate of plates. They were not 

conspicuous in small-scale photography and scrapes of carbonate and mobile fauna. The differences may

be due to sites, scales, and analytical methods. Both other studies include a greater range of depth. Both 

also scraped and photographed large areas on platforms. This may have the effect of sampling across

faunal patches. The smaller samples of this study may have sampled within patches and missed largerscale depth changes. Analytically, Gallaway and Lewbel (1982) did not employ similarity and cluster

analysis. They depended upon abundance of select fauna to describe depth-associated changes. Dokken 

used Bray-Curtiss similarity and cluster analysis on composite data (images plus scrapes). The results

showed such distinct depth zonation that the clustering algorithm may have been one that preserves

sequences. Such methods are used in stratigraphy when zones are known to occur. 

The strongest depth patterns were found in the settling-plate component. The significant negative 

correlation between depth and attached community dry weight is consistent with an exponential decrease 

in the rate of cover development with depth. Such decreases are expected in algae and algal-grazing 

fauna due to light attenuation. The pattern observed in this study is probably not light related, since the 

primary contribution to community dry weight is suspension-feeding barnacle and bryozoan tests. The

depth decrease is most likely a function of decreasing food encounter. Two factors determine encounter 

rate, concentration of food particles and the flow rate of food-bearing water past the feeding structures.

Neither of these was measured during the study, but depth decreases are reasonable for both. During 

summer months, extreme warming can produce sufficient temporary stratification to retain high plankton

concentrations at the upper depths (1 and 5 m). Flow rate will be a function of orbital water movement 

under waves rather than currents for the depths of this study. This orbital flow decreases exponentially

with depth. 

4.1.3 Duration Relationship 

Although the initial design included time-series sampling by all methods, such was only 

accomplished in the settling-plate component. Even in that component, unfortunately, inability to harvest 

plates according to a balanced design of depth and durations makes it difficult to confidently determine 

duration effects. At GI-94, weight versus duration showed no significant correlation (r = -0.11) over the 

190 to 392 day experiments. At GC-18 the same correlation was significant (r = -0.45) over the 90 to 

525 days of the experiment, but unexpectedly negative. The most valid conclusion that can be drawn is 

that duration and dry weight did not show a simple significant positive correlation. This was in spite of

the simple supposition that colonization on a bare plate should increase with time in some manner. Aside 

from confounding of depth and duration effects, two ecological factors may be involved. 

1. Initiation Dates—Colonization occurs when competent larvae encounter and accept

the substrate. Plates deployed when larval conditions are optimal may be colonized 

immediately. Plates deployed long before optimal conditions may be colonized after 

a long wait. A collection of both types of plates will show a neutral or negative 

correlation between duration and degree of cover. 

2. Grazing—The exposed flat surface of the settling plate offers far less refuge from

predation than the adjacent rugose crust until a heavy cover is developed. One plate 

at GC-18 had two predatory snails (Thais sp.) foraging on its surface. Over a long 

period of time and over a large area, grazing and new recruitment should come into

equilibrium such that cover is relatively stable and unrelated to additional duration of

exposure. For small plates and short durations, the likelihood of predation without

ensuing recolonization and compensation prior to plate harvest may be very high.

Such predation would produce neutral to negative correlation with duration. 

34
Resolution of date-of-initiation effects is possible in the future through extensive short-duration 

deployments, but may be logistically impractical. Grazing effects might be discerned and quantified 

through the use of caging experiments with appropriate controls. Development of exclusion systems that

do not alter the small-scale hydrologic regime required by the settling larvae will, however, be a major

challenge. 

4.1.4 Production of Epibiotoic Crusts 

Obtaining accurate and precise measurement of primary, secondary, and higher productivity at

offshore platforms is a technically challenging task that was not attempted in this study. Population age/

size relationships can be used to estimate overall population export (Beaver et al. 2003) under certain

assumptions, but these methods are of no use for estimating production rates of colonial and film forming

organisms. Considerable technique development remains to be undertaken. One finding of this study is 

that the accumulated weight of carbonate material may be a useful and simply obtained measure of net

productivity over extended time intervals. Such measurements were obtained only in the settling-plate 

component. 

A comparison between the settling plate results at GC-18 and GI-94 must be made cautiously due to 

the difference in duration experienced at both and the lack of replication at other platforms in the same

general region. The two platforms do, however, appear to be developing crusts at different rates, the 

more offshore GC-18 slower than the more inshore. Three processes may be involved. 

1. Larval Exposure—Plates at GI-94 tended to be heavily settled with barnacles and

bryozoans. Plates at GC-18 were sparsely settled. While mortality between

settlement and harvest is unknown, the possibility exists that GI-94 experienced 

greater exposure to competent larvae due to proximity of sources or local retention of 

water masses.

2. Water Column Productivity—High weights at GI-94 were associated with large 

barnacles and large bryozoan mats, indicating that post-settlement growth is an

important factor. By contrast, barnacles and bryozoan patches at GC-18 were small. 

Indications are that filter feeders at GI-94 had a greater supply of food material in the 

adjacent water. 

3. Grazing—The dry weight measurements used are standing stock and not actual 

production. It is possible that both platforms have similar production rates, but that 

greater predatory grazing at GC-18 produces the misleading appearance of limited

production. 

The settling plate findings that production at GC-18 is less, is in contrast with the visual impression of

the platforms and the scrape sampling. Subjectively from video, both platforms seem to have similarly

developed types and amounts of encrusting fauna. Cementing bivalves tended to form a base layer

colonized by barnacles and tree oysters. The maximum dry weight of fouling was approximately 2.0g/

cm2

 found on a plate deployed at 5 m on GI-94 for 190 days. The plate was covered with a single to

double layer of barnacles. Typical dry weights for this crust were 3.0 to 4.0g/cm2

. If the crust production

values at the two platforms are actually different, then the crust-forming organisms at GC-18 must be of 

greater average age. 

4.1.5 Ecological Scenario: a Vertical Benthos 

From the results reported here and a review of previous work, an ecological scenario can be

developed that helps identify information needs. The over-riding characteristic of structure communities 

is that they are a vertical benthos deriving their primary small-scale habitat structure from biogenic 

carbonate crusts deposited by barnacles (balanoids), cementing bivalves (Chama, Lopha, etc.), and 

byssate bivalves (Isognomon, Arcidae, etc.). All of these foundation species are suspension feeders

depending on the passing ocean water for nutrition. The extent of habitat development is limited by a

balance between loss of shells and tests and new settlement plus growth. In a vertical benthos, shell

material falls away rather than contributing to a growing carbonate base. Rather than reach a stable

35
climax, platform communities are in a constant state of turnover. The mechanisms of loss can be

proposed, but details and rates remain to be established. These include: predation, age-dependent 

mortality, competitive exclusion, bioerosion, corrosion of underlying metal, and wave surge. 

The carbonate foundation species compete for space with adjacent individuals and with overgrowing 

colonial organisms (sponges, hydroids, anemones, bryozoans, etc.). Larger sponges and colonies of 

bryozoans deprive underlying organisms of food, killing them. These overgrowths are also suspension 

feeders depending on the surrounding ocean for food particles, but the small size for the feeding apparatus 

indicates a dependence on very small plankton, including bacteria. Collectively, they represent a different 

trophic route than the carbonate foundation species. The relative importance of macro, micro, and nanno

filtration to overall platform production has not been determined. Similarly, the consumers of these 

overgrowths are poorly known. 

Attached algae represent a special component of the platform system, since they are primary

producers. As such, they fuel local food chains that can be independent of the surrounding plankton

production. Rates of production and consumption by herbivores are very poorly known. During the

course of this study, scanning electron micrographs of settlement plate surfaces revealed cleanly sheared 

algal stypes a fraction of a millimeter long (Shaughnessy, per com.). The observation that algae are 

abundant only on the top few meters of a platform may be misleading. Algal production may be high over

the top several meters, but grazing is so intense that little biomass accumulates. The algal-based

component of platform systems needs additional study. 

In the present study large consumers of fouling organisms were limited to Thais (gastropod) and 

Arbacia (echinoid). Small consumers (amphipods, ophiuroids, and polychaetes) were abundant. The

paucity of larger animals may simply reflect the realities of a vertical benthos; they eventually fall off. 

Smaller forms occupy the interstices of the carbonate matrix and are less likely to be lost. The trophic 

position of the small consumers is poorly known and largely unquantified. Specialized forms like 

pycnogonids feed hypodermically on hydrozoans. Amphipods are assumed to graze upon hydroids and 

possibly algae. Others may be part of a necrophagous/copraphagous food chain that feeds on biota killed

by overgrowth and fecal material from the suspension feeders. The availability and persistence of a 

detrital resource must be strongly controlled by two factors, retention in the carbonate matrix versus 

flushing into the surrounding ocean by currents and surge. 

The dynamics that cause more inshore platforms to be different than more offshore are essentially 

unknown. Oceanographic phenomena such as salinity, temperature, light attenuation, suspended material,

etc. are highly likely to play important roles. Until the geography of the biotic transition is known,

however, it is not possible to better assess what these roles might be. Biotic control remains a fully open 

question. Since the major plankton food source cannot be regulated by the platform community,

important biotic interactions would most likely be (1) moderators of post-settlement competition and (2)

moderators of crust loss. Predation, especially by fish, and bioerosion are processes that require detailed

investigation. It is unlikely, however, that platforms ever become fully “reef-like” in the stable sense

proposed by Bull and Kendall (1994). A climax will note be reached due to the unavoidable shedding of 

the carbonate crust in a vertical benthos will keep opening new patches for settlement from a frequently

changing larval pool. Episodes and areas of biotic control may be quite transient. 

4.1.6 Items for Future Investigation 

From the present study and review of past work five high priority ecological questions can be posed 

about the artificial substrate communities in the Gulf of Mexico. These questions may not be

management relevant in a strict sense, but they all contribute to the over riding question of what is the 

platform community doing? Answering these questions will be more important as the shift to fewer

depth-spanning structures begins. 

1. Habitat Equilibrium—What are the major processes of fouling community habitat 

accretion and destruction? At what rates do they proceed, and what determines the

equilibrium condition across the northern Gulf of Mexico? 

2. Trophic Structure—What is the overall quantitative primary and higher production 

on structures with special emphasis on routes to species of interest? Investigation 

should include suspension feeding, predation, necrophagy/copraphagy, and attached

36
algae. Development of effective methods is the primary limitation in obtaining an

answer. 

3. Larger Geographic Pattern—Do structures east of the Mississippi River draw from 

the same species pool as structures to the west? Aside from issues of taxonomic 

quality assurance, there are no restrictions on answering this question through 

additional survey. 

4. Better Resolution of Offshore Patterns—Where does the transition from inshore to

offshore communities occur along the coast, and with what oceanographic features 

does the shift coincide? Is there a distinct transition between offshore and bluewater 

communities at some region along the shelf? Both questions could be answered by

means of additional surveying. 

5. Causes of Patterns—What biotic and abiotic factors cause the shift from inshore to 

offshore communities? Answering this question will require autecological

investigation of dominant species and innovative experimental manipulation. 

4.2 UTILITY OF METHODS

This study employed a suite of methods that provided data on a range of spatial scales and taxonomic 

resolution. The following discussion and proposed design and logistics for future studies are based upon 

the experience gained. 

4.2.1 Image-Based Methodology

Video and photographic methods are extremely appealing since they produce a very high data yield

from the divers’ time in the water. The results of this study have shown that video is an excellent means 

of conveying general information about a platform’s biota, and that smaller-scale photography produces 

useful inventory data and illustration of patterns. The overall value of these methods, however, can best 

be judged in the context of a diving program that is time and personnel limited. Large amounts of time

should not be devoted to video survey. In a large-scale survey, adequate video and high resolution 

photography can be undertaken as a lower level of activity. Video survey of a single leg suffices to

capture major inter-platform differences. The value of high-resolution photography can be increased, if 

used in conjunction with scrape samples. The scrape site can be photographed before and after scraping

and a series of images taken around the scrape to determine the spatial extent of the sampled biota. 

4.2.2 Biota Sampling Methods 

Biota were directly sampled by means of scraping and settlement plate recovery. The former sampled 

the time-integrated fouling crust, but with poor quantification. The latter are easily quantified, but sample 

only species that settle and survive until harvest. The scrape samples were the most informative with

respect to overall community composition. In addition, the samples retained some spatial relationship 

among organisms. Supplemented with still images, scrape samples provide an excellent means of

understanding overall system structure. This study did not attempt to assure consistent quantitative 

sampling. Pre-bagging of a scraped area as done by Fotheringham (1981) or use of a grab-like sampler 

(George and Thomas 1979) would improve quantification and retention of mobile fauna. These additions, 

however, will increase the time and effort needed to collect samples. In a large-scale survey, the benefits 

of a large number of samples versus fewer high-quality samples must be weighed. 

Settling plate studies have been included in previous Gulf platform surveys, but the results have

usually been presented as being secondary to scrape sampling except for Pequegnat and Pequegnat

(1968). With respect to overall assessment of biota, scrape sampling alone suffices. Recruitment could 

also be determined from scrape samples, but with greater difficulty due to the complexity of the substrate.

This study, settling plates provided two types of special information. First and most important, they

showed dramatically that recruitment and fouling community developments rates are strongly depth

dependent. Rate measurements cannot be obtained from scrapes. Second, they provided large samples of

encrusting algae and bryozoans in a form more easily studied than in scrape samples. 

37
This study followed the standard oceanographic procedure of bulk preservation with excess formalin 

(10%) in the field followed by water soaking and transfer to ethanol for long-term archival. This

technique usually assures preservation, hardens tissues sufficiently to allow subsequent sectioning of 

organs, and eliminates specimen spoilage. Unfortunately, it makes small organisms too brittle for detailed

examination of morphology, and it denatures DNA to a degree that hinders genetic studies. The 

hardening problem proved especially troublesome for algae, sponges, athecate hydroids, and athecate 

bryozoans. Although time demanding, future sampling should include more careful handling of 

exemplars, relaxation, and use of the taxa-specific preservation recommended by experts. DNA kits can

be used in the field, or specimens dehydrated in absolute ethanol or deep frozen for molecular analysis. 

4.2.3 Settling Plate System 

The settling plate deployment was a qualified success that can be used in future studies with minor 

modification. Unless intentionally cut, as at GC-18, off-the-shelf ratchet cargo belts are strong enough to 

stay in place more than a year at and below 5 m. They are cheap, readily available, and light weight in air 

and water. Shallower, wave action is much greater and failure due to abrasion will be a problem with any 

fiber belt. Steel cable or chains must be used. Attachment of settling plates to the belt with heavy-duty 

cable ties was effective. Ties could be easily cut, and a plate replaced with little difficulty.

The most serious problem encountered was inability to deploy and recover plates according to the 

original design due to weather, operational constraints, and narrow windows of opportunity associated 

with working off the platforms. In order to be effective, sampling designs must make greater allowance

for disruptions. A are minor problem was associated with record keeping. Each plate had a serial number

engraved adjacent to one mounting hole. This made it simple to know what plate was being installed. On 

recovered plates, however, the number was usually obscured by fouling organisms. This required that a 

numbered tag be bagged in with each plate. The plate serial number could only be determined by

scraping the organisms off during analysis. During this project, printed paper tags were used that did not

stand up under preservation. In future studies, chemically resistant plastic tags should be used and affixed 

to each plate with a cable wrap by the diver. 

The PVC plastic plates were colonized, but the question remains open as to how effective the surface

is as a settlement substrate. The paucity of Isognomon bicolor and other bivalves common in scrape

samples may indicate avoidance or loss during collection. Barnacles were strongly attached and usually 

left a basal plate when scraped off. Bryozoa, algae, and sponges, however, were easily scarped off the

plates without residue. These forms may easily be dislodged in the field. Future studies might

incorporate a variety of materials with effectiveness being evaluated via an analysis of variance. 

4.3 LOGISTICS OF ANSWERING AND UNANSWERED QUESTIONS

In the 20+ years since Gallaway and Lewbel’s synthesis of offshore platform ecology, age and 

geography of structures has changed appreciably. The fouling communities of old structures have 

matured, the density of structures across the shelf environment has increased, and rigid structures have 

been emplaced at depths of 1000 m beyond the edge of the shelf. As a result of increased stakeholder

interest in fisheries issues, there has been considerable advancement in the sampling and description of 

fish populations associated with offshore structures (Stanley and Scarborough-Bull 2003 and references 

therein). Platform fish populations have been better surveyed (Rademacher and Render 2003), the zone 

of influence determined acoustically (Stanley and Wilson 2003), and early life histories considered 

(Hernandez et al. 2003). It has become increasingly apparent that the encrusted community interacts with

the fish populations, providing food and habitat. The extent to which specific habitat types influence fish 

populations remains unknown, and the routes and rates of trophic transfer not directly measured. 

Narrow management-related questions about the encrusting biota itself have arisen. Notably, to what

extent do platforms serve as sources and stepping stones for alien species, and to what extent do platforms

serve as extended habitat for desirable species and refuges from destructive trawling? The answers to all

of these management-relevant questions can be incorporated into the framework of five ecological 

questions outlined in section 4.1.6. Clearly, some questions of biogeography can be answered now with 

wide-scale surveys and attention to taxonomic problems. Others that require rate measurements require 

technique development and testing. The experiences of this project provide suggestions for improved

survey logistics. 

38
4.3.1 Design and Logistics for a Large-Scale Survey

Based upon the utility of the various data types and the difficulty of SCUBA operations, the 

following mode of operation is suggested for future large-scale surveys. Experimental methods, such as 

settling plates and rate measurements, are omitted due to the need for additional development. A largescale survey would sample along six shore to shelf break transects of 10 platforms (60 total) from south 

Texas to Alabama using oil and gas as well as navigation and communication structures. 

1. Reconnaissance Digital Video—The primary use of digital video is to provide a 

quick and simple means of conveying the nature of each individual platform.

Approximately one hour of footage along two vertical legs and representative 

horizontal members within 20 m of the surface is sufficient. Data-quality video 

requires for camera angle, distance to object, and lighting are too restrictive. Video is 

best used for illustration, not data. 

2. Photo, Scrape, and Photo (PSP)—Photography (digital or film) will be most 

informative if directly combined with scrape sampling. A pre-scrape and post-scrape 

image will allow for reconstruction of position and quality control on scraping. 

Innovation is needed to improve scraping efficiency, retention, and quantification. In

the absence of better techniques, simple manual scraping with quick bagging to

capture mobile fauna is sufficient. An area of 25 cm x 35 cm should be adequate and 

practical. 

3. Vessel-Based—Platform-based diving operations were used in this study for practical 

and fiscal reasons. It appears, however, that vessel-based operations afford a greater

degree of operational flexibility. Unanticipated operational conflicts could be 

worked around, and a list of primary and contingency sites could be visited as 

needed. 

4. 20 m and Above— Ideally, platforms should be surveyed from surface to bottom, but 

practical limits must be set. In the present study 99% of all taxa were collected

within the top 20 m of water. Species composition continues to shifts a greater

depths, but the overall species inventory remains relatively constant. Working deeper 

greatly decreases diver work time due both to additional swimming and to safely

decompress. 

5. Depth Strata—Sampling (PSP) should be stratified by depth. The current study’s

upper limit of 1 m was insufficient to sample the highly productive and diverse 

surface zone. Depths of 0, 1, 5, 10, 15, and 20 m should be sufficient. The 

shallowest will be most impacted by weather and surge. Greater depths can be

surveyed by a special team at a few sites.

6. Replication—The current study found that both sampled legs were fairly similar as 

long as sampling is extensive enough to collect over biotic patches typically a meter 

or less in diameter. Therefore, a more informative large-scale survey design may

increase the number of platforms visited by eliminating replicate sampling of legs 

within platforms. Within depth strata, however, replication of PSP samples should be 

as extensive as practical. Ten replicates should be taken at each depth at each site (60

samples per platform). Randomization of replicates could be accomplished by

randomly marking a chain and wrapping it around the platform leg. Samples would 

be taken at marked points.

7. Teams—SCUBA sampling teams should consist of three divers. Two teams can

work on the same platform leg simultaneously. A safety and sample-collecting boat 

with a driver and safety diver must be standing by. The overall dive team would 

consist of 8 people. 

39
5 CONCLUSION 

The algal-invertebrate growth sampled on offshore platforms ST-54, GI-94, and GC-18 are typical of

biota found by previous studies in the same region and westward. The well-known barnacles and

bivalves creating the main carbonate matrix of the crust are found from the mouth of the Mississippi 

westward to the limit of survey off Texas. Patterns eastward are unknown. The east-west pattern of lessknown overgrowths of algae, sponges, and colonial forms is obscured by problems of species 

identification that can be resolved by a unified large-scale survey and better taxonomic quality assurance.

The same is the case for small mobile fauna, such as highly abundant amphipods. 

A distinct inshore-offshore change in fauna has been noted by all studies and was found here as well. 

Inshore platforms are dominated by dense populations of smaller barnacles covered with a relatively thin

layer of algae and hydroids. Offshore platforms are dominated by a mix of cementing bivalves, byssate

bivalves, and larger barnacles. This layer is overgrown and fatally smothered at places by sponges,

hydroids, and bryozoa. The causes of the inshore-offshore zonation are unknown and a transition region

has not been sampled. It is anticipated that carbonate-depositing forms reflect a longer integration of time 

than soft-tissue over growths and small mobile fauna. As such, barnacles and bivalves better reflect

biogeographic processes, while the others have very high variances associated with short-term settlement 

and survival events. 

For most species, there is little published information as to their preferred natural habitat. Therefore, 

it is not possible to assess their presence and role in fouling communities as “typical” or “unusual.” 

There is one occurrence that appears to be “unusual”, and there may be others. The tree oyster, 

Isognomon bicolor, is a byssate bivalve that forms numerous dense clusters on offshore platforms, but 

occurs only rarely inshore. Its natural habitat, however, is the prop roots of coastal mangroves, and its

apparently greater success far offshore is unexplained. Biological interaction on platforms may be

different than naturally encountered. 

The entire fouling community is a continuously accreting and shedding system. Settlement is

dependent upon the fluctuating larval supply in the surrounding water. The carbonate depositing fauna

and soft-organism overgrowths are all dependent upon the surrounding water for food. Growth of the 

encrusting matrix is ultimately limited by destructive processes rather than food. Predation, competitive 

exclusion, and bioerosion directly remove crust or weaken it to the point that wave surge strips it off. The 

rates of crust formation and destruction are intertwined with trophic transfers within the fouling 

community and predator/grazing fish. Mechanisms of these processes are poorly understood and rates 

unknown. 

This study employed common image-based and specimen-sampling methods of survey, in addition to

experimental settling plate deployments. Each method yielded some useful information about the biota at 

each site. When funding and dive time are limited, however, certain activities are more informative for 

the cost and time involved. Video surveys are useful for illustration and developing an overall view of

whole-platform ecology, but medium resolution seriously limits the quality of data that can be obtained.

Photographs provided percent cover data and information about patterns of overgrowth, but failed to

reveal the complexity of bivalve cover at the more offshore sites. Direct scrape samples provided the

most complete data, but were not conducted in a manner that allowed quantification. 

The only experiment attempted was the use of settling plates to determine the nature and rates of 

ongoing settlement. Unfortunately, the experiment proved too complex and demanding to be completed 

while dive opportunities were lost to weather and platform operations. The experiments did, however, 

show significant depth effects and inter-platform differences in development of a biofouling crust. Future

use of settling plates should be considered in conjunction with other techniques for direct measurement of 

rate processes. Such techniques, unfortunately, require development. 

The overall effectiveness of the project was negatively impacted by unanticipated problems

associated with carrying out time-series studies from platforms. The GC-18 and ST-54 platforms initiated

major drilling or re-drilling during the study, greatly restricting diving opportunities. The effectiveness of

future studies may be improved by basing diving operations on research vessels and designing 

contingency surveys that target more than one candidate structure in ocean areas of interest. 

41
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APPENDIX A 

 

CHECKLIST OF ALGAE SPECIES 
A-3 

Compiled by Frank Shaunagessy, Humbolt State University 

Reference specimens are maintained at the LSU Herbarium. 

Because the majority of algal literature for the northern Gulf of Mexico is 25-35 years old, it is currently 

not possible to contrast the Louisiana algal flora, or specifically platform algal communities, to any of the 

better studied algal floras along the southeast states and Caribbean. Being able to make reliable floral 

comparisons among geographic locations is an important first step in understanding where platform algae 

are being dispersed from and the abiotic and biotic processes that are likely to be important to platform 

ecosystems. Thus, we used more recent floral treatments by Schneider and Searles (1991) and Wynne 

(1986) from the southeast states and the Atlantic western tropics in order to update specific epithets from 

the Louisiana literature. Dawes (1974) is the taxonomic reference for the cyanobacteria as he provides 

useful drawings and black/white photographs. Most studies used to produce this list of updated names are 

only from Louisiana but one study (Eiseman and Blair 1982) extends to the Louisiana/Texas border at the 

Flower Gardens and another study (Earle 1969; subregion A) covers eastern Louisiana to mid Alabama. 

The algae listed by Bert and Humm (1979) from eight Louisiana oil platforms on an east/west transect is 

also included as well as taxa identified to date in the present study which samples platforms on a north/

south transect. 

Taxa 

Cyanophyta 

Chroococcales 

Chroococcaceae 

Agmenellum thermale (Kützing) Drouand and Daily 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), Humm 

and Bert (1979) 

Anacystis aeruginosa (Zanardini) Drouand and Daily 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979) 

Anacystis dimidiata (Kützing) Drouand and Daily 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979) 

Anacystis marina (Hansgirg) Drouet and Daily 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Bert (1979) 

Anacystix montona (Lightfoot) Drouand and Dailey 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Coccochloris elabens (Brébisson) Drouand and Daily 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Coccochloris stagnina Drouet and Daily 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Entophysalis conferta (Kützing) Drouand and Dailey 

Taxonomic reference: Dawes (1974) 
A-4 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), present study 

Entophysalis deusta (Meneghini) Drouand and Daily 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979) 

Gomphosphaeria aponina Kützing 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Humm and Bert (1979) 

Johannesbaptistia pellucida Taylor and Drouand 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Nostocales 

Oscillatoriaceae 

Microcoleus chthonoplastes (Flora Danica) Thurand 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Microcoleus lyngbyaceus (Kützing) Crouan 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Synonyms from Louisiana studies: as Lyngbya confervoides, Lyngbya semiplena, Lyngbya aestuarii, 

Hydrocoleum lyngbyaceum by Humm and Caylor (1957); as Lyngbya majuscula by Humm and 

Darnell (1959), present study 

Microcoleus vaginatus (Vaucher) Gomont 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Oscillatoria erythraea (Ehrenberg) Kützing 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Synonyms from Louisiana studies: as Trichodesmium thiebautii by Humm and Caylor (1957), 

Humm and Bert (1979) 

Oscillatoria lutea Agardh 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979) 

Synonyms from Louisiana studies: as Lyngbya lutea by Humm and Caylor (1957), Humm and Bert 

(1979) 

Oscillatoria subuliformis (Thwaites) Gomont 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Phormidium submembranaceum (Ardissone and Strafforello) Gomont 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Synonyms from Louisiana studies: as Oscillatoria submembranacea 

Ardissone and Strafforello by Bert and Humm (1979), Humm and Bert (1979) 

Plectonema nostocorum Borand 

Cited in the following Louisiana studies: Humm and Caylor (1957) 
A-5 

Plectonema terebrans Bornand and Flahault 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Porphyrosiphon kurzii (Zeller) Drouet 

Cited in the following Louisiana studies: Humm and Bert (1979)

Porphyrosiphon notarisii (Meneghini) Kützing 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Synonyms from Louisiana studies: as Oscillatoria nigro-viridis by Humm and Caylor (1957), present 

study 

Schizothrix arenaria (Berkeley) Gomont 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Synonyms from Louisiana studies: as Microcoleus tenerrimus by Humm and Caylor (1957), as 

Schizothrix tenerrima by Bert and Humm (1979) and Humm and Bert (1979) 

Note: S. tennerrima is not listed as a synonym of S. arenaria by Dawes (1974) but, given the use of 

'tenerrimus', we are treating S. tenrrima as a synonym of S. arenaria. 

Schizothrix calcicola (Agardh) Gomont 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Synonyms from Louisiana studies: as Lyngbya epiphytica by Humm and Caylor (1957), present 

study 

Schizothrix mexicana Gomont 

Taxonomic reference: Dawes (1974) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Synonyms from Louisiana studies: as Lyngbya gracilis by Humm and Darnell (1959), present study 

Spirulina subsalsa Oersted 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), Humm 

and Bert (1979) 

Synonyms from Louisiana studies: as Spirulina major by Humm and Caylor (1957), present study 

Symploca atlantica Gomont 

Taxonomic reference: this species is not mentioned by Dawes but all species of Symploca cited by 

Dawes are considered synonyms of Schizothrix arenaria. 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Nostocaceae 

Nodularia harveyana (Thwaites) Thurand 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Nodularia spumigena Mertens var. major (Kützing) Bornet and Flahault 

Taxonomic reference: Dawes (1974)

Synonyms from Louisiana studies: as Nostoc spumigena by Humm and Bert (1979) 

Note: Nostoc spumigena (Mertens) Drouet is not synonomized into N. spumigena by Dawes but, 

given that the species name and authority are the same, we are treating N. spumigena as being 

synonymous with N. spumigena. 
A-6 

Stigonemataceae 

Amphithrix violecea (Kützing) Bornet and Flahault 

Taxonomic reference: genus and species not mentioned by Dawes 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Mastigcoleus testarum Lagerheim 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979) 

Rivulariaceae 

Calothrix confervicola (Roth) C. Agardh 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957), present study 

Calothrix crustacea Thuret 

Taxonomic reference: Dawes (1974)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), present study 

Chlorophyta

Tetrasporales 

Pseudotetraspora marina Wille 

Taxonomic reference: Wynne (1986), genus and species not included in Schneider and Searles 

(1991) 

Synonyms from Louisiana studies: as Pseudotetraspora antillarum by Bert and Humm (1979), 

Humm and Bert (1979) 

Ulotrichales 

Ulotrichaceae 

Gomontia polyrhiza (Langerheim) Bornand and Flahault 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Monostroma oxyspermum (Kützing) Doty 

Taxonomic reference: Schneider and Searles (1991), not in Wynne (1986) 

Cited in the following Louisiana studies: Humm and Bert (1979) 

Ulothrix flacca (Dillwyn) Thuret 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Bert (1979), Kapraun (1974) 
A-7 

Ulvales 

Ulvellaceae 

Entocladia viridis Reinke 

Taxonomic reference: Schneider and Searles (1991); as Acrochaete viridis in Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979) 

Epicladia testarum (Kylin) R. Nielsen 

Taxonomic reference: Wynne (1986), Edwards (1976)

Synonyms from Louisiana studies: as Entocladia testarum Kapraun (1974), present study 

Phaeophila dendroides (Crouan) Batters 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), 

Kapraun (1974) 

Phaeophila floridearum Hauck 

Taxonomic reference: species not mentioned by either Schneider and Searles (1991) or Wynne (1986) 

or Dawes (1974) 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Pseudoclonium marinum (Reinke) Alleem and Schulz 

Taxonomic reference: Wynne (1986), Dawes (1974), questionable record of the genus noted in 

Schneider and Searles (1991)

Cited in the following Louisiana studies: Humm and Bert (1979), as Protoderma marinum by Bert 

and Humm (1979) 

Note: Kapraun (1974) lists a species within this genus from Louisiana as 'P. submarinum'. Based on 

examination of the species lists above, we consider 'submarinum' to be an orthographic variant of 

marinum.. 

Stichococcus marinus (Wille) Hazen 

Taxonomic reference: Wynne (1986), not mentioned in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979) 

Ulvella lens Crouan 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Darnell (1959), Bert 

and Humm (1979), Humm and Bert (1979), Kapraun (1974) 

Ulvaceae 

Blidingia marginata (J. Agardh) P. Dangeard 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Blidingia minima (Kützing) Kylin 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Enteromorpha clathrata (Roth) J. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), Humm 

and Bert (1979), Mullahy (1959), Kapraun (1974) 
A-8 

Enteromorpha compressa (L.) Nees 

Taxonomic reference: Schneider and Searles (1991), as E. compressa (L.) Greville in Wynne 

(1986), Dawes (1974) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Enteromorpha flexuosa J. Agardh 

Taxonomic reference: Schneider and Searles (1991), and Wynne (1986) with ssp. forma

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), Mullahy (1959), Kapraun (1974) 

Synonyms from Louisiana studies: as Enteromorpha lingulata, Enteromorpha plumosa by Humm and 

Caylor (1957), Bert and Humm (1979), Humm and Bert (1979), Mullahy (1959), Kapraun (1974), as 

Enteromorpha erecta by Bert and Humm (1979), Humm and Bert (1979) 

Enteromorpha intestinalis (L.) Nees 

Taxonomic reference: Schneider and Searles (1991), as E. intestinalis (L.) Link in Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Enteromorpha linza (L.) J. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974), present study 

Enteromorpha prolifera (O.F. Muller) J. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), as E. 

salina by Bert and Humm (1979) and Humm and Bert (1979), Kapraun (1974) 

Enteromorpha ramulosa (J.E. Smith) Carmichael 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Ulva curvata (Kützing) De Toni 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Bert (1979) 

Ulva rigida C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Ulva lactuca by Humm and Caylor (1957), Eiseman and Blair 

1982, Mullahy (1959), Kapraun (1974) 

Cladophorales 

Anadyomenaceae 

Anadyomene stellata (Wulfen) C. Agardh 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Microdictyon boergesenii Sandchell 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 
A-9 

Boodleaceae 

Struvea sp. 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Cladophoraceae 

Chaetomorpha brachygona Harvey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Chaetomorpha gracilis Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979) 

Chaetomorpha linum (O.F. Müller) Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Kapraun 

(1974) 

Chaetomorpha minima Collins and Hervey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979) 

Cladophora albida (Nees) Kützing 

Taxonomic reference: Schneider and Searles (1991)

Cited in northern Gulf flora by: Bert and Humm (1979) 

Note: Schneider and Searles (1991) cite one study from the southeastern states where C. albida was 

misidentified as Cladophora delicatula. 

Cladophora catenata (L.) Kützing 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Cladophora coelothirx Kützing 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Cladophora repens by Bert and Humm (1979), Kapraun 

(1974) 

Cladophora dalmatica Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Kapraun 

(1974), present study 

Synonyms from Louisiana studies: as C. fascicularis by Mullahy (1959) 

Cladophora montagneana Kützing

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Cladophora delicatula Montagne by Humm and Darnell 

(1959), Bert and Humm (1979), Humm and Bert (1979) 
A-10 

Cladophora sericea (Hudson) Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Synonyms from Louisiana studies: as Cladophora gracilis by Humm and Caylor (1957), Bert and 

Humm (1979), and Humm and Bert (1979), as Cladophora flexuosa (Dillwyn) Harvey by Bert and 

Humm (1979) 

Cladophora socialis Kützing 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as C. constricta by Bert and Humm (1979) 

Cladophora vagabunda (Linnaeus) van den Hoek 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Synonyms from Louisiana studies: as Cladophora fascicularis by Humm and Caylor (1957), as 

Cladophora brachyclona Montagne Bert and Humm (1979) 

Siphonocladaceae 

Cladophoropsis membranacea (C. Agardh) Børgesen 

Taxonomic reference: Wynne (1986) Cited in the following Louisiana studies: Humm and Darnell 

(1959), Kapraun (1974), Bert and Humm (1979) 

Note: Schneider and Searles (1991) cite two studies from the southeastern states where Cladophora 

pellucidoidea van den Hoek was misidentified as C. membranacea. 

Rhizoclonium africanum Kützing 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Rhizoclonium hookeri by Bert and Humm (1979), Humm and 

Bert (1979), Kapraun (1974) 

Rhizoclonium kochianum Kützing 

Taxonomic reference: Dawes (1974), not mentioned by either Schneider and Searles (1991) or 

Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), Humm 

and Bert (1979), Kapraun (1974) 

Rhizoclonium riparium (Roth) Harvey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), Mullahy (1959), Kapraun (1974) 

Synonyms from Louisiana studies: as Rhizoclonium kerneri by Humm and Bert (1979) 

Rhizoclonium tortuosum Kützing 

Cited in the following Louisiana studies: Humm and Bert (1979) 

Valoniaceae 

Valonia macrophysa Kützing 

Taxonomic reference: Wynne (1986), not cited by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Valonia ventricosa J. Agardh 

Taxonomic reference: Wynne (1986), not cited by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 
A-11 

Caulerpales 

Bryopsidaceae 

Bryopsis pennata Lamouroux 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979) 

Bryopsis plumosa (Hudson) C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Kapraun (1974) 

Bryopsis hypnoides Lamouroux 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Derbesia vaucheriaformis (Harvey) J. Agardh 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Note: Schneider and Searles (1991) cite two studies from the southeastern states where Derbesia 

marina (Lyngbye) Solier was misidentified as D. vaucheriaformis

Derbesia turbinata Howe and Hoyt 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: present study 

Pedobesia lamourouxii (J. Agardh) J. Feldmann, Loreau, Codomier, and Couté 

Taxonomic reference: Wynne (1986)

Synonyms from Louisiana studies: as Derbesia lamourouxii (J. Agardh) Solier by Bert and Humm 

(1979) 

Note: Schneider and Searles (1991) cite one study from the southeastern states where Derbesia 

marina (Lyngbye) Solier was misidentified as D. lamourouxii.. 

Caulerpaceae 

Caulerpa microphysa (Weber van Bosse) Feldman

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Caulerpa prolifera (Forskål) Lamouroux 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Caulerpa racemosa var. laetevirens (Montagne) Weber-van Bosse 

Taxonomic reference: Schneider and Searles (1991), this variety not in Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Synonyms from Louisiana studies: as Caulerpa peltata by Eiseman and Blair (1982) 

Caulerpa racemosa (Forsskål) J. Agardh var. racemosa

Taxonomic reference: Wynne (1986), this variety not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Codiaceae 

Codium taylorii (Silva) 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 
A-12 

Ostreobiaceae 

Ostreobium quekettii Bornet and Flahault 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979) 

Udoteaceae 

Halimeda discoidea Decaisne 

Taxonomic reference: Wynne (1986), genus not cited by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Halimeda gracilis Harvey ex J. Agardh 

Taxonomic reference: Wynne (1986), genus not cited by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Udotea cyanthiformis Decaisne 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Udotea flabellum (Ellis and Solander) Lamouroux 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Dasycladales 

Batophora oerstedii J. Agardh 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Note: Schneider and Searles (1991) cite this species as cast ashore unattached in drift only. 

Chrysophyta

Vaucheria velutina C. Agardh 

Taxonomic reference: Schneider and Searles (1991)

Synonyms from Louisiana studies: as Vaucheria thuretii Woronin by Humm and Caylor (1957) 

Phaeophyta

Phaeophyceae 

Ectocarpales 

Ectocarpaceae 

Acinetospora crinita (Carmichael ex Harvey in Hooker) Kornmann 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979) 

Bachelotia antillarum (Grunow) Gerloff 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Kapraun 

(1974), Earle (1969) 

Ectocarpus elachistaeformis Heydrich 

Taxonomic reference: after examination Schneider and Searles (1991) considered this a valid taxon 

but Wynne (1986) put it under Feldmannia elachistaeformis
A-13 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), Earle (1969) 

Ectocarpus siliculosus (Dillwyn) Lyngbye 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Kapraun (1974), Earle (1969), 

present study 

Synonyms from Louisiana studies: as Ectocarpus confervoides, Ectocarpus dasycarpus (E. 

dasycarpus only mentioned by Wynne (1986)) by Humm and Caylor (1957), Humm and Bert 

(1979), Mullahy (1959), Kapraun (1974), Earle (1969) 

Ectocarpus variablis Vickers 

Taxonomic reference: Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979) 

Feldmannia irregularis (Kützing) Hamel 

Taxonomic reference: Wynne (1986)

Synonyms from Louisiana studies: as Giffordia conifera by Bert and Humm (1979) 

Herponema tortugense (W. Taylor) W. Taylor 

Taxonomic reference: Wynne (1986), species not included in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Hincksia irregularis (Kützing) Amsler 

Taxonomic reference: Schneider and Searles (1991)

Synonyms from Louisiana studies: as Ectocarpus rallsiae by Humm and Darnell (1959), as Giffordia

rallsiae in Humm and Bert (1979), Kapraun (1974), Earle (1969) 

Hincksia mitchelliae (Harvey) Silva in Silva 

Taxonomic reference: Schneider and Searles (1991)

Cited in the following Louisiana studies: present study 

Synonyms from Louisiana studies: as Ectocarpus mitchelliae by Humm and Caylor (1957), Mullahy 

(1959), as Giffordia mitchelliae and Giffordia indica (Sonder) Papenfuss and Chihara in Papenfuss 

by Bert and Humm (1979), Humm and Bert (1979), Earle (1969), Kapraun (1974). 

Note: Schneider and Searles (1991) cite studies from the southeast states where H. mitchelliae was 

misidentified as G. indica. Although Schneider and Searles (1991) did not synonomize G. indica with 

H. mitchellieae, we treat G. indica as a synonym of H. mitchelliae because ‘indica’ does not appear 

to exist as a taxon (is this true?). 

Hincksia ovata (Kjellman) P.C. Silva in Silva, Me—ez, and Moe 

Taxonomic reference: Schneider and Searles (1991)

Synonyms from Louisiana studies: as Ectocarpus intermedius by Bert and Humm (1979), Kapraun 

(1974), Earle (1969) 

Note: E. intermedius is not treated by either Schneider and Searles (1991) or Wynne (1986) but 

Schneider and Searles (1991) do cite Giffordia intermedia as a synonym of H. ovata. In Wynne 

(1986) as Giffordia ovata. 

Phaeostroma pusillum Howe and Hoyt 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Earle 

(1969) 

Spongonema tomentosum valid taxon? 

Taxonomic reference: genus and species not in Schneider and Searles (1991), Wynne (1986), or 

Taylor (1967) 

Cited in the following Louisiana studies: Bert and Humm (1979) 
A-14 

Note: see p. 142 in Earle (1969) for description 

Streblonema oligosporum Stromfelt 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Kapraun (1974) 

Chordariales 

Chordariaceae 

Cladosiphon zosterae (J. Agardh) Kylin 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Kapraun (1974) 

Synonyms from Louisiana studies: as Eudesme zosterae (J. Agardh) Kylin by Humm and Darnell 

(1959) 

Cladosiphon occidentalis Kylin 

Taxonomic reference: 

Cited in the following Louisiana studies: Earle (1969) 

Myrianemataceae 

Hecatonema floridanum

Taxonomic reference: Schneider and Searles (1991)

Cited in the following Louisiana studies: present study 

Myrionema orbiculare J. Agardh 

Taxonomic reference: Wynne (1986), not cited by Schneider and Searles (1991)

Synonyms from Louisiana studies: as Ascocyclus orbicularis Magnus by Bert and Humm (1979) 

Note: Schneider and Searles (1991) accept the distinction between Myrionema magnusii (Sauvageau) 

Lamouroux and M. orbiculare. 

Myrionema strangulans Greville 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), present study 

Sphacelariales 

Sphacelariaceae 

Sphacelaria rigidula Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: present study 

Synonyms from Louisiana studies: as Sphacelaria furcigera by Humm and Darnell (1959), Bert and 

Humm (1979), Humm and Bert (1979), Kapraun (1974), Earle (1969) 

Sphacelaria tribuloides Meneghini 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Kapraun 

(1974), Earle (1969) 

Dictyotales 

Dictyotaceae 

Dictyota bartayresii Lamouroux 

Taxonomic reference: Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982), Kapraun (1974). 
A-15 

Dictyota cervicornis Kützing 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Earle (1969) 

Dictyota menstrualis (Hoyt) Schnandter, Hörnig and Weber-Peukert 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Dictyota dichotoma by Humm and Caylor (1957), Humm 

and Darnell (1959), Eiseman and Blair (1982), Mullahy (1959), Kapraun (1974), Earle (1969) 

Dictyopteris justii Lamouroux 

Taxonomic reference: Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Lobophora variegata (Lamouroux) Womersley 

Taxonomic reference: Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982), Kapraun (1974) 

Padina gymnospora (Kützing) Sonder 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Synonyms from Louisiana studies: as Padina vickersiae by Humm and Caylor (1957), Humm and 

Darnell (1959), Mullahy (1959), Kapraun (1974), Earle (1969) 

Padina jamaicensis (Collins) Papenfuss 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991)

Synonyms from Louisiana studies: as Padina sanctae-crucis Børgesen by Kapraun (1974) 

Spatoglossum schroederi (C. Agardh) Kützing 

Taxonomic reference: Wynne (1986), Schneider and Searles (1991)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Stypopodium zonale (Lamouroux) Papenfuss 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Dictyosiphonales 

Striariaceae 

Hummia onusta (Kützing) Fiore 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Earle 

(1969) 

Synonyms from Louisiana studies: Stictyosiphon subsimplex, Myriotrichia subcorymbosa (Holden) 

Blomquist by Earle (1969) 

Myriotrichiaceae 

Myriotrichia clavaeformis Harvey 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Myriotrichia repens Hauck by Humm and Bert (1979) 

Fucales 

Cystoseiraceae 

Turbinaria tricostata Barton 

Taxonomic reference: Wynne (1986), family not in Schneider and Searles (1991)

Cited in the following Louisiana studies: Kapraun (1974)—in drift only! 
A-16 

Sargassaceae 

Sargassum acinarium (L.) C. Agardh 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Kapraun (1974), Earle (1969) 

Sargassum filipendula C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Mullahy (1959), Kapraun (1974), 

Earle (1969) 

Sargassum fluitans Børgesen 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), Kapraun (1974), Earle (1969), present study 

Sargassum natans (Linnaeus) Meyen 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Mullahy 

(1959), Kapraun (1974), Earle (1969) 

Scytosiphonales 

Scytosiphonaceae 

Rosenvingea intricata (J. Agardh) Børgesen 

Taxonomic reference: Wynne (1986), genus but not species cited in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Kapraun (1974) 

Rhodophyta

Rhodophyceae 

Bangiophycidae 

Porphyridiales 

Porphyridiaceae 

Chroodactylon ornatum (C. Agardh) Basson 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Asterocytis ramosa by Bert and Humm (1979) 

Stylonema alsidii (Zanardini) Drew 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Synonyms from Louisiana studies: as Goniotrichum alsidii by Bert and Humm (1979), Humm and 

Bert (1979), present study 

Compsopogonales 

Erythropeltidaceae 

Erythrocladia endophloea Howe 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Erythrocladia recondita, Erythrocladia vagabunda by Bert 

and Humm (1979) 

Erythrotrichia carnea (Dillwyn) J. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), Humm and Bert (1979), Mullahy 

(1959), Kapraun (1974), present study 
A-17 

Sahlingia subintegra (Rosenvinge) Kornmann 

Taxonomic reference: Schneider and Searles (1991), Erythrocladia subintegra not cited by Wynne 

(1986) although he does list Erythropeltis subintegra 

Cited in the following Louisiana studies: present study 

Synonyms from Louisiana studies: as Erythrocladia subintegra by Bert and Humm (1979), Kapraun 

(1974) 

Bangiales 

Bangiaceae 

Bangia autropurpurea (Roth) C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974), Humm and Bert (1979), present study 

Florideophycidae 

Acrochaetiales 

Acrochaetiaceae 

Acrochaetium antillarum W. Taylor 

Taxonomic reference: Wynne (1986), not cited by Schneider and Searles (1991) as a species of 

Audouinella

Cited in the following Louisiana studies: Bert and Humm (1979) 

Acrochaetium flexuosum Vickers 

Taxonomic reference: Wynne (1986), not cited by Schneider and Searles (1991) as a species of 

Audouinella

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), 

Kapraun (1974) 

Audouinella densa (Drew) Garbary 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: present study 

Audouinella gracilis (Børgesen) Garbary 

Taxonomic reference: Wynne (1986), gracilis not in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Acrochaetium gracile by Bert and Humm (1979), Humm and 

Bert (1979) 

Audouinella hallandica (Kylin) Woelkerling 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Acrochaetium dufourii by Bert and Humm (1979) 

Audouinella hoytii (Collins) C.W. Schneider 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Acrochaetium hoytii by Bert and Humm (1979) 

Audouinella hypneae (Børgesen) Lawson and John 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Acrochaetium seriatum by Humm and Caylor (1957), Bert and 

Humm (1979) 

Audouinella microscopica (Nägeli) Woelkerling 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: present study 
A-18 

Synonyms from Louisiana studies: as Acrochaetium crassipes by Humm and Caylor (1957), Mullahy 

(1959), Kapraun (1974), as Acrochaetium trifilum by Bert and Humm (1979) 

Note: Schneider and Searles (1991) considered Taylor’s (1960) Kylinia crassipes to be Audouinella 

microscopica. In addition, Wynne (1986) lists Audouinella crassipes, Kylinia crassipes, etc. as 

synonyms of A. microscopica. Neither Schneider and Searles (1991) or Wynne (1986) mention 

Acrochaetium crassipes but, given the above uses of crassipes, it seems likely that the Humm and 

Caylor’s (1957) material is Audouinella microscopica.

Audouinella sancti-thomae (Børgesen) Garbary 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Acrochaetium sancti-thomae by Bert and Humm (1979) 

Audouinella saviana (Meneghini) Woelkerling 

Taxonomic reference: Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Acrochaetium thurettii by Bert and Humm (1979), as 

Acrochaetium sagraeanum by Bert and Humm (1979), Humm and Bert (1979) 

Note: Schneider and Searles (1991) cite a study where Audouinella densa (Drew) Garbary is 

misidentified as A. thurettii.

Audouinella secundata (Lyngbye) Dixon 

Taxonomic reference: Schneider and Searles (1991) 

Synonyms from Louisiana studies: as Acrochaetium virgatulum Humm and Bert (1979) 

Nemaliales 

Galaxauraceae 

Galaxaura oblongata (Ellis and Solander) Lamouroux 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Synonyms from Louisiana studies: as Galaxaura cylindrica (Ellis and Solander) Lamouroux by 

Eiseman and Blair (1982) 

Gelidiales 

Gelidiaceae 

Gelidium latifolium (Greville) Bornet and Thuret 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: present study 

Synonyms from Louisiana studies: as Gelidium corneum (Hudson) Lamouroux by Humm and Caylor 

(1957) 

Note: Schneider and Searles (1991) do not include G. latifolium in the flora of the southeastern 

states. In addition, Schneider and Searles (1991) cite several studies where Gellidium pusillum

(Stackhouse) Le Jolis from the southeastern states was misidentified as G. corneum. 

 Among other characters, material we have collected from platforms is flat and stoloniferous 

which, if we accept the similarity of the illustration of G. corneum in Humm and Caylor (1957) and 

Wynne (1986) as the taxonomic reference, then our material has to be G. latifolium. If we use 

Schneider and Searles (1991) as a reference, then we must either list G. corneum as a valid taxon or 

identify our material as Gelidium americanum (W.R. Taylor) Santelices, which is the closer of the 

two species listed by Schneider and Searles (1991). Schneider and Searles (1991) do not synonomize 

G. corneum. Also, they have examined no ‘G. corneum' material from the Gulf of Mexico. [Get the 

paper by Stewart and Norris (1981) on Gelidium species from the Gulf of Mexico.] 

Gelidium americanum (W.R. Taylor) Santelices 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Pterocladia americana by Bert and Humm (1979) 
A-19 

Corallinales 

Corallinaceae 

Amphiroa rigida var. antillana Børgesen 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Amphiroa tribulus (Ellis and Solander) Lamouroux 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Fosliella farinosa (Lamouroux) Howe 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Mullahy (1959), Humm and 

Darnell (1959), Bert and Humm (1979) 

Synonyms from Louisiana studies: as F. f. var. callithamnioides in Bert and Humm (1979), as F. f. 

var solmsiana in Bert and Humm (1979), as F. atlantica in Bert and Humm (1979) 

Jania adhaerens Lamouroux 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979), present study 

Jania capillacea Harvey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) includes J. capillacea in Jania 

adhaerens

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Pneophyllum lejolisii (Rosanoff) Chamberlain 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Fosliella lejolisii (Rosanoff) Howe by Humm and Caylor 

(1957), Humm and Darnell (1959), as Heteroderma lejolisii by Kapraun (1974) 

Lithophyllum pustulatum (Lamouroux) Foslie 

Taxonomic reference: Campbell and Woelkerling (1990) 

Synonyms from Louisiana studies: as Dermatolithon pustulatum by Kapraun (1974) 

Gigartinales 

Gymnophloeaceae 

Titanophora incrustans (J. Agardh) Feldmann 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Halymeniaceae 

Cryptonemia sp. 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Grateloupia filicina (Wulfen) C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Eiseman and Blair (1982) 

Hypneaceae 

Hypnea musciformis (Wulfen) Lamouroux 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 
A-20 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Darnell (1959), 

Humm and Bert (1979), Mullahy (1959), Kapraun (1974) 

Hypnea valentiae (Turner) Montagne 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Synonyms from Louisiana studies: as Hypnea cornuta by Kapraun (1974) 

Hypnea pannosa J. Agardh 

Taxonomic reference: Taylor (1967) lists this taxon as an ‘uncertain record’ 

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Kallymeniaceae 

Kallymenia westii Ganesan 

Taxonomic reference: Schneider and Searles (1991)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Peyssonneliaceae 

Peyssonnelia inamoena Pilger 

Taxonomic reference: Schneider and Reading (1987), Wynne (1986) 

Cited in the following Louisiana studies: present study 

Peyssonnelia rubra (Greville) J. Agardh 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Note: Schneider and Searles (1991) cite several studies from the southeastern states where 

Peyssonnelia inamoena Pilger was misidentified as P. rubra. 

Peyssonnelia simulans Weber-van Bosse in Børgesen 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986)

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Phyllophoraceae 

Gymnogongrus tenuis J. Agardh 

Taxonomic reference: Wynne (1986), species not mentioned by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Solieriaceae 

Agardhiella subulata (C. Agardh) 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Agardhiella tenera by Humm and Caylor (1957), Humm and 

Darnell (1959), Mullahy (1959), as Solieria tenera by Kapraun (1974) 

Note: S. tenera is not synonomized by either Schneider and Searles (1991) or Wynne (1986) but 

‘tenera’ is synonomous with A. subulata according to Wynne (1986). 

Gracilariales 

Gracilariaceae 

Gracilaria caudata J. Agardh 
A-21 

Taxonomic reference: Wynne (1986), species not mentioned by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Gracilaria foliifera (Forsskål) Børgesen 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Darnell (1959), Bert 

and Humm (1979), Humm and Bert (1979), Mullahy (1959), Kapraun (1974) 

Note: Schneider and Searles (1991) cite several studies from the southeast states where Gracilaria 

tikvahiae McLachlan was misidentified as G. foliifera. 

Gracilaria verrucosa (Hudson) Papenfuss 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Bert (1979) 

Gracilariopsis lemanaeformis (Bory) Dawson, Acleto and Foldvik 

Taxonomic reference: Schneider and Searles (1991)

Synonyms from Louisiana studies: as Gracilariopsis sjoestedtii by Humm and Bert (1979) 

Note: as Gracilaria lemanaeformis in Wynne (1986) 

Rhodymeniales 

Rhodymeniaceae 

Botryocladia occidentalis (Børgesen) Kylin 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Chrysymenia halymenioides Harvey 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Coelarthrum albertsii (Piccone) Børgesen 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Fauchea hassleri Howe and W. Taylor 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Ceramiales 

Ceramiaceae 

Anotrichium tenue (C. Agardh) Nägeli 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Synonyms from Louisiana studies: as Griffithsia tenuis by Humm and Darnell (1959), Kapraun 

(1974) 

Antithamnion cruciatum (C. Agardh) Nägeli 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Bert and Humm (1979), present study 

Antithamnionella elegans

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: present study 

Callithamnion sp. 

Cited in the following Louisiana studies: present study 
A-22 

Ceramium byssoideum Harvey 

Taxonomic reference: Schneider and Searles (1991), as Ceramium flacidum by Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), 

Kapraun (1974) 

Ceramium fastigiatum (Roth) Harvey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Kapraun 

(1974) 

Ceramium fastigiatum var. flaccidum H. Pandersen 

Taxonomic reference: Wynne (1986), Schneider and Searles (1991) 

Cited in the following Louisiana studies: as Ceramium fastigiatum var. flaccida by Bert and Humm 

(1979) 

Ceramium tenuissimum (Roth) Areschoug 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Mullahy (1959) 

Note: Schneider and Searles (1991) cite studies from the southeast states where Ceramium 

fastigiatum f. flaccidum H. Petersen in Børgesen was misidentified as C. tenuissimum. 

Compsothamnion thuyoides (J.E. Smith) Schmitz 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Spyridia filamentosa (Wulfen) Harvey in Hooker 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Darnell (1959), 

Mullahy (1959), Kapraun (1974) 

Note: Schneider and Searles (1991) cite several studies from the southeast states where Spyridia 

hypnoides (Bory) Papenfuss was misidentified as S. filamentosa. 

Spermothamnion investiens (P. and H. Crouan in Schramm and Mazé) Vickers 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979) 

Note: Schneider and Searles (1991) cite several studies from the southeastern states where Lejolisia 

exposita C.W. Schneider and Searles was misidentified as S. investiens. 

Dasyaceae 

Dasya corymbifera J. Agardh 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Dasya baillouviana (S.G. Gmelin) Montagne 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Synonyms from Louisiana studies: as Dasya pedicellata by Mullahy (1959) 

Delesseriaceae 

Apoglossum ruscifolium (Turner) J. Agardh 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 
A-23 

Caloglossa leprieurii (Montagne) J. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Kapraun (1974) 

Hypoglossum tenuifolium (Harvey) J. Agardh 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Searlesia subtropica (C.W. Schneider) C.W. Schneider and Eiseman 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Eiseman and Blair (1982) 

Rhodomelaceae 

Bostrichia radicans (Montagne) Montagne 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Bert (1979), Kapraun 

(1974); includes f. moniliforme

Bostrichia tenella (Vahl) J. Agardh 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Bert (1979) 

Chondria collinsiana Howe 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Kapraun (1974) 

Chondria dasyphylla (Woodward) C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Chondria leptacremon (Melvill) Dandoni 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Caylor (1957) 

Chondria temuissima (Goodenough and Woodward) C. Agardh 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Kapraun (1974) 

Digenea simplex (Wulfen) C. Agardh 

Taxonomic reference: Wynne (1986), not mentioned by either Schneider and Searles (1991) or 

Dawes 

Cited in the following Louisiana studies: Humm and Darnell (1959), Mullahy (1959), Kapraun (1974) 

Herposiphonia secunda (C. Agardh) Falkenberg 

Taxonomic reference: Wynne (1986); the latter also recognizes f. secunda, f. tenella (C. Agardh) 

Wynne (1986) with Herposiphonia tenella (C. Agardh) Nägeli as a synonym of H. secunda f. 

tenella. 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979) 

Note: Schneider and Searles (1991) have a different treatment of species in this genus and cite several 

studies from the southeast states where H. tenella (not recognized by Wynne (1986)) was 

misidentified as H. secunda. 

Laurencia papillosa (C. Agardh) Greville 

Taxonomic reference: Wynne (1986) 

Cited in the following Louisiana studies: Bert and Humm (1979) 
A-24 

Laurencia poiteaui (Lamouroux) Howe 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) recognized Laurencia poitei 

(Lamouroux) Howe but Silva et al. (1987) explained that L. poitei is a synonym of L. poiteaui. 

Synonyms from Louisiana studies: as Laurencia poitei by Humm and Darnell (1959), Humm and 

Bert (1979), Kapraun (1974), as Laurencia gemmifera Harvey by Mullahy (1959), Kapraun (1974) 

Note: Schneider and Searles (1991) cite studies suggesting that L. gemmifera is conspecific with L. 

poiteaui.

Lophosiphonia cristata Falkenberg 

Taxonomic reference: Wynne (1986), genus not included in Schneider and Searles (1991) 

Cited in the northern Gulf flora by Bert and Humm (1979) 

Lophosiphonia obscura (J. Agardh) Falkenberg in Engler and Prantl 

Taxonomic reference: Wynne (1986), genus not in Schneider and Searles (1991) 

Synonyms from Louisiana studies: as L. subadunca by Bert and Humm (1979), Humm and Bert 

(1979) 

Lophosiphonia sacchoriza Collins and Hervey 

Taxonomic reference: Dawes (1974), species not mentioned by Wynne (1986), genus and species not 

mentioned by Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Humm and Darnell (1959), 

Kapraun (1974) 

Polysiphonia atlantica Kapraun and Norris 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: present study 

Polysiphonia boldii Wynne and Edwards 

Taxonomic reference: Wynne (1986) 

Synonyms from Louisiana studies: as Polysiphonia hemishperica by Bert and Humm (1979), Humm 

and Bert (1979) 

Polysiphonia denudata (Dillwyn) Greville ex Harvey 

Taxonomic reference: Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Synonyms from Louisiana studies: as Polysiphonia variegata by Humm and Caylor (1957), Mullahy 

(1959) 

Polysiphonia echinata Harvey 

Taxonomic reference: Wynne (1986), not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Humm and Bert (1979), 

Kapraun (1974) 

Polysiphonia havanensis Harvey 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Bert and Humm (1979), 

Kapraun (1974) 

Polysiphonia howei Hollenberg 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979) 

Polysiphonia ramentacea Harvey 

Taxonomic reference: Wynne (1986), species not in Schneider and Searles (1991) 

Cited in the following Louisiana studies: Mullahy (1959), Kapraun (1974) 
A-25 

Polysiphonia subtilissima Montagne 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Caylor (1957), Bert and Humm (1979), Humm 

and Bert (1979), Kapraun (1974) 

Wrightiella tumanowiezii (Gatty) Schmitz 

Taxonomic reference: Schneider and Searles (1991), Wynne (1986) 

Cited in the following Louisiana studies: Humm and Darnell (1959), Kapraun (1974) 

Literature Cited in Appendix 1 

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Earle, S.A. 1969. Phaeophyta of the eastern Gulf of Mexico. Phycologia 7:71-254. 

Edwards, P. 1976. Illustrated Guide to the Seaweeds and Seagrasses in the Vicinity of Port Aransas, 

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A-26 

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flora. Bot. Mar. 29:131-135. 

Ballantine, D.L. and M.J. Wynne. 1986. Notes on the marine algae of Puerto Rico II. Additions of 

Ceramiaceae (Rhodophyta) including Ceramium vergoniae sp nov. Bot. Mar. 29:497-502. 

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Chapman, V.J. 1961. The Marine Algae of Jamaica: I. Myxophyceae and Chlorophyceae. Bull. Instit. 

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Edwards, P. and D.F. Kapraun. 1973. Benthic marine algal ecology in the Port Aransas, Texas area. 

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Edwards, P. 1969. Field and cultural studies on the seasonal periodicity of growth and reproduction of 

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Guzman, S.C. 1965. Notas preliminares sobre un reconocimiento de la flora marina del estado de 

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Hamm, D. and H. J. Humm. 1976. Benthic algae of the Anclote Estuary II. Bottom-dwelling species. 

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Humm, H. J. 1964. Epiphytes of the sea grass Thalassia testudinum. Florida Bulletin of Marine Science. 

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Humm, H. J. and H. H. Hildebrand. 1964. Marine algae from the Gulf Coast of Texas and Mexico. Contr. 

mar. Sci. 8:227-268. 
A-27 

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Chlorophyta and Phaeophyta. Germany: J. Cramer. 173 pp. 

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APPENDIX B 

 

VIDEO PERCENT COVER DATA 
B-3 

ST54 Video Percent Cover (Point Count) 100 points per depth 

Depth m. Bare Turf Barnacle Bacterial Encrusting Hydroids Bryozoans Algae 

 Film Sponge (2) 

1 25 20 43 0 0 5 0 5 

1 10 25 39 0 0 8 0 2 

1 0 22 24 0 0 12 0 2 

1 5 12 28 0 0 12 0 7 

1 2 20 40 0 0 4 0 1 

1 1 15 38 0 0 9 0 1 

2 2 12 41 0 5 15 0 1 

3 1 12 37 0 0 21 0 2 

4 1 15 38 0 11 37 0 2 

5 0 20 30 0 0 50 0 3 

5 5 15 30 0 5 50 0 4 

5 0 20 10 0 20 50 0 1 

5 0 10 60 0 15 25 0 4 

5 0 30 25 0 5 10 0 5 

6 0 45 10 0 0 20 0 7 

7 0 25 20 0 5 40 0 8 

8 0 35 30 0 20 10 0 5 

9 0 30 25 0 20 30 0 0 

10 0 30 17 0 15 45 0 0 

10 5 25 13 0 15 45 0 0 

10 1 25 15 0 5 54 0 0 

10 0 20 27 0 2 53 0 0 

10 2 18 46 0 0 35 0 0 

11 0 30 26 0 5 40 0 0 

12 1 65 11 0 5 19 0 0 

13 0 65 10 0 5 18 0 0 

14 0 50 20 0 10 10 0 0 

15 0 50 21 0 10 10 0 0 

16 0 65 36 10 0 0 0 0 

17 0 55 36 12 5 5 0 0 

18 0 55 36 15 5 5 0 0 

19 0 55 36 15 5 5 0 0 

20 0 10 60 20 0 10 0 0 

20 0 12 50 30 0 8 0 0 

20 0 12 50 30 0 8 0 0 

20 0 12 50 30 0 8 0 0 

20 0 12 50 30 0 8 0 0 
B-4 

GI94 Video Percent Cover (Point Count) 100 points per depth 

Depth m. Bare Turf Barnacle Standing Encrusting Hydroids Bryozoans Tunicates Bivalves

 Sponge (1) Sponge (2) 

1 30 0 60 10 0 0 0 0 0 

1 10 0 10 80 0 0 0 0 0 

1 10 0 10 80 0 0 0 0 0 

1 0 0 100 0 0 0 0 0 0 

5 0 55 5 30 10 0 0 0 0 

5 1 59 15 5 20 0 0 0 0 

5 0 33 5 2 50 10 0 0 0 

5 0 33 5 0 50 10 0 0 0 

6 0 20 0 0 40 40 0 0 0 

6 0 40 20 0 30 10 0 0 0 

7 0 25 35 0 10 30 0 0 0 

8 0 50 0 0 25 20 5 0 0 

8 0 55 0 0 10 10 25 0 0 

9 0 30 0 0 10 5 55 0 0 

10 0 50 0 0 0 50 0 0 0 

10 0 45 0 0 0 50 5 0 0 

10 0 75 0 0 0 25 0 0 0 

10 0 38 0 2 0 20 20 0 0 

10 0 40 0 0 0 20 20 0 0 

10 0 40 25 0 10 10 15 0 0 

11 0 85 0 0 5 5 5 0 0 

12 0 73 2 0 5 15 5 0 0 

13 0 73 2 0 10 5 0 0 0 

14 0 59 1 0 0 10 30 0 0 

15 0 23 0 0 2 5 70 0 0 

16 0 23 0 0 2 5 70 0 0 

17 0 23 0 0 2 5 70 0 0 

18 0 10 0 0 5 10 75 0 0 

19 0 10 0 0 5 10 75 0 0 

20 0 5 0 0 0 50 45 0 0 

20 0 20 0 0 75 0 5 0 0 

20 0 5 2 0 80 0 13 0 0 

20 0 20 0 0 75 0 5 0 0 

20 0 5 2 0 80 0 13 0 0 

21 0 5 2 0 80 0 13 0 0 

22 0 15 0 0 0 0 5 80 0 

23 0 15 0 0 0 0 5 80 0 

24 0 10 0 0 30 5 5 50 0 

25 0 30 0 0 25 5 10 30 0 

26 0 50 0 0 30 5 5 0 10 

27 0 50 0 0 30 5 5 0 5 

28 0 40 0 0 20 40 0 0 0 

29 0 50 0 0 20 10 5 10 5 

30 0 50 0 0 20 20 10 0 0 

30 0 20 0 0 20 10 50 0 0 

30 0 20 0 0 20 10 50 0 0 

30 0 33 10 0 50 5 2 0 0 

30 0 50 5 0 30 5 2 1 0 
B-5 

GC-18 Video Percent Cover (Point Count) 100 points 

Depth Bare Turf Barnacle Standing Encrusting Hydroids Bryozoan Tunicates Bivalves Algae Anemones

 Sponge Sponge 

1 0 15 5 0 10 15 0 0 0 20 55 

1 2 17 8 0 2 12 0 0 0 22 37 

1 3 26 8 0 5 12 0 0 0 17 29 

1 1 25 15 0 7 13 0 0 0 15 12 

1 0 15 2 0 9 6 0 0 0 8 30 

2 0 5 1 0 10 2 0 0 0 5 17 

3 1 12 2 0 5 21 0 0 0 9 10 

4 2 22 5 0 2 21 0 0 0 11 5 

5 0 24 0 0 10 30 0 0 0 20 2 

5 0 21 5 0 5 24 0 0 0 15 3 

5 0 32 7 0 2 22 0 0 0 5 5 

5 0 40 10 0 5 25 0 0 0 25 0 

5 0 45 8 0 3 12 0 0 0 5 0 

6 2 35 7 0 10 15 0 0 2 2 2 

7 6 10 25 0 0 30 0 0 0 0 3 

8 0 12 10 0 15 18 0 0 1 2 1 

8 2 11 12 0 0 45 0 0 0 2 0 

9 0 5 20 0 20 65 0 0 0 0 0 

10 20 10 15 0 0 0 0 0 5 30 0 

10 5 25 15 0 0 35 0 0 10 15 0 

10 0 30 10 0 0 60 0 0 0 0 0 

10 0 35 5 0 5 40 0 0 0 5 0 

10 8 25 4 0 0 60 0 0 0 0 0 

11 0 5 2 0 85 10 0 0 0 0 0 

12 0 15 7 0 15 20 5 0 2 0 0 

13 2 11 15 0 12 50 0 0 0 0 0 

14 1 22 5 0 0 35 2 0 0 0 0 

15 0 21 15 0 2 27 2 0 1 0 0 

16 0 10 12 0 5 27 0 0 0 0 0 

17 3 28 5 0 12 51 1 0 0 0 0 

18 0 27 20 0 5 47 3 0 0 0 0 

19 3 20 17 0 25 53 2 0 0 0 0 

20 0 30 10 0 5 60 2 0 0 0 0 

20 10 20 15 0 10 45 10 0 0 0 0 

20 0 15 0 0 5 80 3 0 0 0 0 

20 0 10 5 0 5 80 4 0 0 0 0 

20 0 15 20 0 45 20 0 0 0 0 0 

21 2 12 5 0 65 10 0 0 0 0 0 
The Department of the Interior Mission

As the Nation's principal conservation agency, the Department of the Interior has responsibility 

for most of our nationally owned public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; 

preserving the environmental and cultural values of our national parks and historical places; 

and providing for the enjoyment of life through outdoor recreation. The Department assesses 

our energy and mineral resources and works to ensure that their development is in the best 

interests of all our people by encouraging stewardship and citizen participation in their care. 

The Department also has a major responsibility for American Indian reservation communities 

and for people who live in island territories under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) 

primary responsibilities are to manage the mineral resources located on the Nation's Outer 

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and Indian 

lands, and distribute those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program 

administers the OCS competitive leasing program and oversees the safe and environmentally 

sound exploration and production of our Nation's offshore natural gas, oil and other mineral 

resources. The MMS Minerals Revenue Management meets its responsibilities by ensuring the 

efficient, timely and accurate collection and disbursement of revenue from mineral leasing and 

production due to Indian tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially 

affected parties and (2) carrying out its programs with an emphasis on working to enhance the 

quality of life for all Americans by lending MMS assistance and expertise to economic 

development and environmental protection.