ACCESS NUMBER: 30991 

STUDY TITLE: Deepwater Program: Northern Gulf of Mexico Continental Slope 

Habitats and Benthic Ecology

REPORT TITLE: Deepwater Program: Northern Gulf of Mexico Continental Slope 

Habitats and Benthic Ecology; Interim Report, Year 2 

CONTRACT NUMBER: 1435-01-99-CT-30991 

SPONSORING OCS REGION: Gulf of Mexico, OCS Region 

APPLICABLE PLANNING AREA: Northern Gulf of Mexico 

FISCAL YEARS OF THE PROJECT: 2000, 2001, 2002, 2003 

COMPLETION DATE OF REPORT: December 2002 

COSTS: 2000: $1,253,359 ; 2001: $1,178, 201 ; 2002: 1,105,657; 2003: $651,490; 

CUMULATIVE PROJECT COST: $4,188,707 

PROJECT MANAGERS: Gilbert T. Rowe and Mahlon C. Kennicutt II 

AFFILIATION: Texas A&M University 

ADDRESS: Texas A&M University, College Station, Texas 77843 

PRINCIPAL INVESTIGATORS*: Gary Wolff, Jody Deming, Ian MacDonald, Paul 

Montagna, Richard Haedrich, John Morse, William Bryant, and Worth Nowlin 

KEYWORDS: Benthic Ecology, Northern Gulf of Mexico, Contaminants, Microbiota, 

Foraminifera, Meiofauna, Macrofauna, Demersal Fishes, Megafauna, Physical 

Oceanography, Hydrography, Geological Oceanography, Biogeochemistry, 

Geochemistry, Ecosystem Health, Ecosystem Modeling, Habitats, Zonation, and 

Carbon Limitation. 

BACKGROUND: Increasing exploration and exploitation of fossil hydrocarbon 

resources in the deep-sea prompted the Minerals Management Service of the U.S. 

Department of the Interior to support an investigation of the structure and function of the 

assemblages of organisms that live in association with the sea floor in the deep-sea. 

The program, Deep Gulf of Mexico Benthos or DGoMB, is studying the northern Gulf of 

Mexico (GOM) continental slope from water depths of 300 meters on the upper 

continental slope out to greater than 3,000 meters water depth seaward of the base of 

the Sigsbee and Florida Escarpments. The study is focused on areas that are the most 

likely targets of future resource exploration and exploitation. However, to develop a 

Gulf-wide perspective of deep-sea communities, sampling in areas beyond those 

thought to be potential areas for exploration has been included in the study design. A 

major enhancement in the program is the extension of the transects onto the abyssal 
ACCESS NUMBER: 30991 

plain of the central Gulf of Mexico through collaborative studies with Mexican scientists. 

This additional work effort will allow assessment of benthic community structure and 

function throughout the basin by sampling the deepest habitats in the region. 

The program is designed to gain a better ability to predict variations in the structure and 

function of animal assemblages in relation to water depth, geographic location, time and 

overlying water mass. Biological studies are integrated with measurements of physical 

and chemical hydrographic parameters, sediment geochemical properties and 

geological characteristics that are known to influence benthic community distributions 

and dynamics. Eight (8) hypotheses are being tested on the basis of measures of 

benthic community structure. 

It is hypothesized that community structure varies as a function of: 

1. water depth, 

2. geographic location (east vs west), 

3. association with canyons, 

4. association with mid-slope basins, 

5. sea surface primary productivity, 

6. proximity to hydrocarbon seeps, 

7. time (seasonal and interannual scales), and 

8. association with the base of escarpments 

OBJECTIVES: The goals of the program are to: 

- determine in greater detail the composition and structure of slope bottom 

biological communities and to infer relationships between biological patterns 

and major controlling processes and 

- characterize the area as to its present “health” and function and compare and 

contrast the region with similar oceanic regions. 

Specific program objectives are to: 

- improve a conceptual model that served as the guide for the design and 

overall conduct of the study and to test specific hypotheses related to the 

models; 

- compile and synthesize data from existing databases and on-going programs 

to interpret new results; 

- conduct field collections to describe the distribution and structure of benthic 

communities on the continental slope of the GOM and to elucidate the 

functional interactions among them in known environmental settings; 

- characterize the hydrographic structure and measure the dissolved and 

particulate water column nutrient concentrations, primary productivity, and 

chlorophyll a at the study sites; 

- characterize the sediments at the study sites including grain size and 

hydrocarbon, metal, carbonate, and organic carbon concentrations; 
ACCESS NUMBER: 30991 

- characterize the basic attributes of the benthic microbiota and biomass at the 

study sites; 

- characterize the soft-bottom macro- and megafauna at the study sites; 

- relate variations in benthic biota patterns to sedimentary processes and to the 

chemical and physical setting; 

- define basic levels of animal and bacterial activity and production and 

describe interactions between and among benthic biota, the several 

ecological/biological compartments, and the abiotic environment; and 

- compare and contrast the GOM benthic marine environment and communities 

with those in other basins of similar depth ranges and oceanic settings. 

DESCRIPTION: The program is to be conducted over a 57-month period of 

performance. Major oceanographic cruises have been conducted, one in each of the 

first two years of the program and two in the third year. The final year of the program will 

be dedicated to completing sample analyses begun in the first three years, data 

management and interpretation, model refinement, and production of the Synthesis 

Report. The field surveys will document the biota, the abiotic character of the slope and 

the important biotic and abiotic forcing factors. Station selection criteria included 

consideration of anticipated zonation, water depth, distance from shore, abiotic 

variables, physiography and topography, geochemical environment, anthropogenic 

effects, and present and future leasing trends. 

 The four tasks of the program and their status: 

 TASK 1 - Re-examination of Existing Data and Field Study Design: Completed 

 TASK 2 - Field Sampling: Completed 

 TASK 3 - Sample and Data Processing and Analysis: Underway 

 TASK 4 - Data Interpretation, Synthesis and Reporting: To be Initiated 

A major enhancement in the program is the extension of the transects onto the abyssal 

plain of the central Gulf of Mexico through collaborative studies with Mexican scientists. 

This additional work effort will allow assessment of benthic community structure and 

function throughout the basin by sampling on the deep Sigsbee Abyssal Plain within the 

Mexican Exclusive Economic Zone (EEZ). 

SIGNIFICANT CONCLUSIONS: Based on the data being generated from the survey 

samples, detailed maps are being constructed which suggest the following: 

1. Biomass and density of each size or functional component decline with depth, 

2. Diversity of each size or functional component reaches a maximum at 

intermediate depths, 

3. Assemblages or re-current groups vary as a function of depth, 

4. Maps of species (dominant) suggest that the Mississippi Trough and the 

DeSoto Canyon harbor unique assemblages of animals characterized by high 

densities and relatively low diversity, and 
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5. Total community metabolism, measured as sediment community oxygen 

demand, declines (log-normal) as a function of depth. 

STUDY RESULTS: The study has resulted in large data sets describing the physics, 

geology, and biology of the sediment and near-sediment environments, at water depths 

ranging from 200 up to 3,700 meters. These data will be analyzed using multivariate 

statistical techniques, including but not limited to Principal Components Analysis and 

MANOVA. These analyses will allow the team to identify general trends related to 

environmental gradients and to test the eight (8) hypotheses listed above. The 

conceptual model will segue into a full-blown numerical simulation of food web 

dynamics, based on biomass and total oxygen consumption measured with a benthic 

lander at the 6 process sites. The internal transfers within the food web will be validated 

from the food web incubation tracer techniques. 

STUDY PRODUCTS: This program will produce 57 Monthly Progress Reports, Two 

Interim Reports, One Final Synthesis Report, Multiple Peer Reviewed Publications, Five 

ITM Sessions, 6 Cruise Plans, 6 Cruise Reports, and Two Planning Meeting Reports. 

*P.I.’s affiliation may be different than that listed for Project Manager(s). 
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Study Area - The Northern Gulf of Mexico