ACCESS NUMBER: 30555 

STUDY TITLE: Northern Gulf of Mexico Continental Slope Chemosynthetic 

Communities Program

REPORT TITLE: Chemosynthetic Ecosystems Study, Final Report - Volume I: 

Executive Summary, Volume II: Technical Report, and Volume III: Appendices 

CONTRACT NUMBER: 14-35-0001-30555 

SPONSORING OCS REGION: Gulf of Mexico 

APPLICABLE PLANNING AREAS: Central and Western 

FISCAL YEARS OF PROJECT FUNDING: 1992-1994 

COMPLETION DATE OF REPORT: November 1992 

COST: FY 1992 

CUMULATIVE PROJECT COST: $375,642.69 

PROJECT MANAGER: Dr. James Brooks 

AFFILIATION: Geochemical and Environmental Research Group Texas A&M 

University 

ADDRESS: 833 Graham Road, College Station, TX 77845 

PRINCIPAL INVESTIGATORS: Dr. James M. Brooks, Dr. Ian MacDonald, Dr. Eric 

Powell, Dr. William Schroeder, Dr. Robert Carney, Dr. Charles Fisher, Dr. Will Sager, 

Dr. Gary Wolff 

KEY WORDS: Chemosynthetic Communities, Oil Seeps, Gulf of Mexico, Continental 

Slope 

BACKGROUND: Numerous descriptive studies of the continental shelf are available. 

In contrast, the topography, geology, geophysics, currents, chemistry, and biota of the 

continental slope are less well known. For the most part, deep-sea animals live under 

conditions of total darkness, low temperature, nearly featureless mud, and sparse food 

resources. They are generally small and fragile. But chemosynthetic animals are 

exceptions to the generality. The first chemosynthetic animals were discovered in the 

Pacific Ocean (Galapagos Rift, 1977). Living near hydrothermal vents in the spreading 

seafloor, these remarkable animals were shown subsequently to obtain their metabolic 

energy from dissolved hydrogen sulfide issuing from the vents. The high density and 

biomass of these very large forms were the exception which proved the rule that the 

main limiting factor to the deep-sea fauna is the availability of nutrients. The 1982 

discovery of well-developed chemosynthetic communities near petroleum seeps in the 
Gulf of Mexico led MMS to require that industry protect them from the physical effects of 

upper continental slope exploration and production. While some investigations have 

been conducted in recent years, there are still few data on the life history and ecological 

interactions within these communities. This study addresses both operational and 

biological questions, the answers to which are needed for effective description, 

detection, and protection of these communities. 

OBJECTIVES: The objectives of this program were to: 

• Gather and synthesize all available information on Gulf of Mexico 

chemosynthetic communities and associated fauna; 

• Develop a conceptual model containing all biotic and abiotic features of 

chemosynthetic communities, which explains the observed patterns of 

distribution and abundance; 

• Appoint a Scientific Review Board for periodic reviews of the quality of data and 

reports and general oversight of the scientific program; 

• Determine quantitatively what animals compromise chemosynthetic communities, 

their spatial and temporal variability, and spatial relationships among animals; 

• Determine the physical-chemical factors (e.g. depth, temperature, water 

chemistry, sediment types, and dissolved gasses) which influence, limit, or 

control the distribution, abundance, and growth of chemosynthetic communities; 

• So far as possible with available information, determine the sources (e.g. deep 

vs. shallow or petrogenic vs. biogenic) of any necessary dissolved gasses and 

the likelihood that petroleum production may ultimately deprive the animals of an 

energy source; 

• Determine whether chemosynthetic communities are robust or fragile and 

whether they are essentially permanent or ephemeral. Characterize the age, 

growth rate, turnover rates, reproduction and recruitment, and patterns of 

senescence and death in the dominant chemosynthetic animals. Also estimate 

recovery rates of communities damaged by physical disturbance; 

• Determine the reliability of methods for detecting chemosynthetic communities 

using remote acoustic and/or geophysical devices, imaging instrumentation, 

hydrocarbon measurements, and/or other available technologies; and 

• Recommend the content of future studies (three to ten years following the 

completion of this study) which will complement the data obtained and detect 

temporal changes. 

DESCRIPTION: In general, this investigation employs remote sensing instrumentation 

(e.g. side-scan sonar and geophysical acoustic devices), bottom samplers (corers), and 
ACCESS NUMBER: 30555 

manned submersibles to collect very detailed and site-specific samples and data. The 

sample design allows the investigators to determine biogeochemical conditions and life 

requirements of chemosynthetic animals on a fine scale. In addition, various in situ 

experiments are designed to address several of the above objectives. 

SIGNIFICANT CONCLUSIONS: The Chemosynthetic Ecosystems Study is a threeyear program that has been undertaken to determine the geological, geochemical, 

physiological, and ecological factors that control the formation and persistence of 

chemosynthetic communities at hydrocarbon seeps. Dense aggregations of 

vestimentiferan tube worms, mytilid mussels, and vesicomyid clams are known to 

colonize natural hydrocarbon seeps in the norther Gulf of Mexico at wide-spread 

locations in water depths of 300 to 2200 m. These animals derive all of their food from 

chemoautotrophic bacterial symbionts, which in turn utilize sulfide and methane 

associated with the seeping hydrocarbons. The aggregations thus exploit a food supply 

entirely decoupled from sunlight and surface productivity. The aggregations generally 

support communities of heterotrophic animals such as fish or crustaceans, many of 

which are common elsewhere on the continental slope. Because the communities are 

comparatively lush, and because they occur in seafloor localities that are likely to be 

near to drilling or energy production activities, there is to be near to drilling or energy 

production activities, there is concern to protect them from possible harmful impact. 

The first annual report reviews literature pertinent to the study and synthesizes 

previously collected data. 

STUDY PRODUCTS: 1995. Chemosynthetic ecosystem study literature review and 

data synthesis, volume I: executive summary. Prepared by Geochemical and 

Environmental Research Group for the U.S. Dept. of the Interior, Minerals Management 

Service, Gulf of Mexico OCS Region, New Orleans, OCS Study MMS 95-0021 LA 29 

pp. 

1995. Chemosynthetic ecosystem study literature review and data synthesis, volume II: 

technical report. Prepared by Geochemical and Environmental Research Group for the 

U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 

New Orleans, LA. OCS Study MMS 95-0022 335 pp. 

1995. Chemosynthetic ecosystem study literature review and data synthesis, volume 

III: appendix. Prepared by Geochemical and Environmental Research Group for the 

U.S. Dept. of the Interior, Minerals Management Service, Gulf of Mexico OCS Region, 

New Orleans, LA. OCS Study MMS 95-0023 236 pp. 

*P.I.’s affiliation may be different than listed for Project Managers.