Nutritional associations among fauna at hydrocarbon seep communities in the Gulf of Mexico

The Gulf of Mexico supports dense aggregations of megafauna associated with hydro- carbon seeps on the Louisiana Slope. The visually dominant megafauna at the seeps — mussels and tube worms — derive their nutrition from symbiotic relationships with sulfide or methane-oxidizing bacteria. The structure of the tube worm aggregations provide biogenic habitat for numerous species of heterotrophic animals. Carbon, nitrogen and sulfur stable isotope analyses of heterotrophic fauna collected with tube worm aggregations in the Green Canyon Lease area (GC 185) indicate that most of these species derive the bulk of their nutrition from chemoautolithotrophic sources. The isotope analyses also indicate that although 2 species may be deriving significant nutritional input from the bivalves, none of the species analyzed were feeding directly on the tube worms. Grazing gastropods and deposit-feeding sipunculids were used to estimate the isotopic value of the free-living chemoau- tolithotrophic bacteria associated with the tube worms (δ13C –32 to –20‰; δ15N 0 to 7‰; δ34S –14 to –1‰). The use of tissue δ34S analyses in conjunction with tissue δ13C and δ15N led to several insights into the trophic biology of the communities that would not have been evident from tissue stable C and N analyses alone.