ABSTRACT
During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over 2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m2) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H. methanicola tissue stable isotope values are consistent with a chemo-autotrophic food source. No evidence of chemo-autotrophic symbionts was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution of hydrates in surface sediments.
Subject(s)
Fossil Fuels , Methane/metabolism , Polychaeta/physiology , Animals , Atlantic Ocean , Caribbean RegionABSTRACT
A large (540 square meters) bed of Bathymodiolus n. sp. (Mytilidae: Bivalvia) rings a pool of hypersaline (121.35 practical salinity units) brine at a water depth of 650 meters on the continental slope south of Louisiana. The anoxic brine (dissolved oxygen =0.17 milliliters per liter) contains high concentrations of methane, which nourishes methanotrophic symbionts in the mussels. The brine, which originates from a salt-cored diapir that penetrates to within 500 meters ofthe sea floor, fills a depression that was evidently excavated by escaping gas. The spatial continuity of the mussel bed indicates that the brine level has remained fairly constant; however, demographic differences between the inner and outer parts of the bed record small fluctuations.