Stable isotope variation among the mussel Bathymodiolus childressi and associated heterotrophic fauna at four cold-seep communities in the Gulf of Mexico

Efforts to determine the utilization of Gulf of Mexico (GOM) chemosynthetic production by benthic predators have relied on stable isotope differences between photosynthetic and chemosynthetic production. Whereas the photosynthetic delta C-13 value in GOM surface waters is relatively uniform, chemosynthetic production may differ in different areas depending on prevalence of thiotrophy versus methanotrophy and inorganic carbon source. In this paper we compare the delta C-13 and delta N-15 signatures of the symbiont-containing mussel, Bathymodiolus childressi Gustafson, 1998, from four different chemosynthetic sites to test the hypothesis that methanotrophic production results in significant differences among them. Bathymodiolus childressi from two areas characterized by brine seepage and biogenic methane (GC425 and GC233) had very low delta N-15 (-3.7 parts per thousand and -16.6 parts per thousand) and delta C-13 (-57.5 parts per thousand and -63.5 parts per thousand) relative to areas with substantial thiotrophic production (GC234 and GC 185). Bathymodiolus childressi from each chemosynthetic community had significantly different delta C-13, and three of the sites also had distinct delta N-15 values. The delta C-13 and delta N-15 signatures of hagfish (Eptatretus sp.) and giant isopods (Bathynomus giganteus) captured from two sites showed little or no chemosyntheic usage. Squat lobsters (Munidopsis sp.) showed heavy incorporation of chemosyntheic production, but did not directly consume B. childressi.