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Investigations of Chemosynthetic Communities on the Lower Continental
Slope of the Gulf of Mexico

Interim Report 1

The largest oil reserves in the continental United States are found in the Gulf of Mexico. The Minerals Management Service (MMS) is responsible for overseeing the responsible extraction of
these natural resources. By the early 1980s, energy companies had developed the technology to explore and extract oil and gas in waters up to 1,000 m deep.
During the mid to late 1980s, MMS contracted with the Geochemical and Environmental Research Group (GERG) at Texas A&M University (TAMU) to collect animals from areas of the deep sea floor associated with active oil and gas seeps. The original expectations of both the
MMS and the scientists involved were that few animals would be found associated with these
“toxic” sea floor environments, and that perhaps the few that were found would be unhealthy at best. However, when the trawls came to the surface over Bush Hill a site that became one of the best studied seep sites in the world, they were so full of animals the nets could only be brought on board with the help of an extra crane. In addition, the animals were not the usual fauna of the deep Gulf of Mexico. The nets were full of giant tubeworms and mussels, which had only recently been discovered at deep-sea hydrothermal vents in the Pacific Ocean. Since that time similar (but different) cold-seep and hydrothermal-vent communities have been discovered in many different geological settings in the world’s oceans.

Over the last 20 years these animals and communities have been studied at moderate depths in the Gulf of Mexico (GoM), along with the geology, geochemistry, and microbiology that allows them to flourish. As a result, the hydrocarbon seep communities in less than 1,000 m on the Upper Louisiana Slope of the Gulf of Mexico, are the most intensively studied and most understood of any deep-sea cold-seep communities in the world. The basic biology of the dominant animals, their life histories, and the biodiversity and biogeography of the seep and coral communities on the Upper Louisiana Slope is now understood. The successional processes
that lead to the eventual development of coral communities on carbonates created during periods of active hydrocarbon seepage is understood. Also discovered are some amazing communities, such as the ice worms that inhabit methane ice and the mussels that ring the Brine Pool NR-1. Meanwhile, energy companies have continued to develop the technology to extract oil and gas from deeper and deeper water and now have the capability to drill oil wells in all water depths in the GoM Outer Continental Slope. Although several GoM hydrocarbon seep sites at depths greater than 1,000 m have been visited by scientists, only a single site has been the focus of more than a few exploratory dives. This site, at 2,200 m in Alaminos Canyon, has lush communities of tubeworms and mussels that are reminiscent of the shallower sites that are well known. However, the underlying geology and almost all of the species present are different. Preliminary studies indicate that the structure of the communities associated with the tubeworms and mussels is also quite different. The normal “background” fauna are different at this depth, and different patterns of interaction between these animals and the seep specific animals are expected. Not only is the ecology of this deep community not understood, at this point the types of communities that exist at depths between 1,000 and 2,200 m are not known. Advances in this understanding and knowledge are the goal of this contract.

The primary purpose of this research is to discover and characterize the sea floor communities that live in association with hydrocarbon seepage and on hard ground in the deep Gulf of Mexico. The sites studied are in areas energy companies will soon drill for oil and gas.

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