Methane ice worms: Hesiocaeca methanicola colonizing fossil fuel reserves

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 rec ently breached the sea floor at a depth of 540 m. The hydrate surface visib le from the submarine was considerably greater than that of any other repor ted hydrate. Two distinct color bands of hydrate were present in the same m ound, and the entire exposed surface of the hydrate was infested (2500 indi viduals/m(2)) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca methanicola, in the polychaete family Hesionidae (Desbruyeres an d Toulmond 1998). H. methanicola tissue stable isotope values are consisten t with a chemoautotrophic food source. No evidence of chemoautotrophic symb ionts was detected, but geochemical data support the presence of abundant f ree living bacteria on the hydrate. The activities of the polychaetes, graz ing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution of hydrates in surface sediments.