Chemoautotrophic production incorporated by heterotrophs in Gulf of Mexico hydrocarbon seeps: An examination of mobile benthic predators and seep residents

摘要

The continental slope of the Gulf of Mexico supports dense aggregations of tubeworms and mussels that have symbiotic chemoautotrophic bacteria. Associated with these communities are numerous heterotrophic fauna and free-living bacteria. Here we examine the stable C, N, and S isotope compositions of fauna from two chemoautotrophic communities to identify isotope ranges of chemoautotrophic primary production and determine the usage of that primary production by heterotrophic invertebrates. The range in isotope values of the chemoautotrophic production is different between sites. A brine seep (GC233) dominated by mussels symbiotic with methanotrophic bacteria has C-13 and N-15 depleted nutrient sources (-50 to -65 parts per thousand and -9 to -12 parts per thousand, respectively), indicating methanotrophy using biogenic methane and suggesting ammonium as the dominant nitrogen source. However, those same sources were S-34-enriched (6 parts per thousand-11 parts per thousand), as indicated by resident heterotrophs (Munidopsis sp., Methanoaricia dendrobranchiata Blake 2000, Ahvinocaris stactophila Williams 1988, Phascolosoma turnerae Rice 1985), indicating that thiotrophy was a minor chemosynthetic method at the site. A site dominated by tube worms and mussels (GC234) has two isotopically distinct sources of carbon, one between -24 and -30 parts per thousand and another of approximately -40 parts per thousand, as indicated by the resident heterotrophs. Resident heterotrophs at GC234 had delta N-15 and delta S-34 values from 1 parts per thousand to 5 parts per thousand and -10 parts per thousand to 6 parts per thousand, respectively. These isotope values suggest a mix of thiotrophy and methanotrophy (largely from thiotrophic sources) at the site. We estimate that hagfish (Eptatretus sp.) captured approximately 2 km from the communities derived at least 10% of their carbon from chemoautotrophic sources because of low delta C-13 values. In contrast, giant isopods (Bathynomus giganteus Milne Edwards, 1879), captured with the hagfish show negligible incorporation of chemosynthetic production.