Abstract
Deep-sea chemosynthetic invertebrates utilize available dissolved compounds (e.g., methane, sulfur) from the surrounding seep environment as a source of energy as well as nutrition by housing bacterial endosymbionts in their gill tissues. While some invertebrates such as the tubeworm (Lamellibrachia sp.) have evolved to entirely rely on their symbiotic companionship for energy, some chemosynthetic bivalves (Bathymodiolus childressi, Bathymodiolus heckerae and Calyptogena pacifica) have retained their functional gut to filter-feed particulates from the water column (e.g., algal and/or detrital) for nutrition and therefore are mixotrophic in their feeding modes. Moreover, different chemosynthetic invertebrates host different endosymbionts: Lamellibrachia and C. pacifica - thiotrophs, B. childressi - methanotrophs, and B. heckerae - consortia of thiotrophs and methanotrophs. These biological differences affect their metabolism and therefore imprint unique molecular and isotopic fingerprints. This study explores for the first time, a more precise isotopic approach to investigate these unique fingerprints for tracing nitrogen sources and assimilation, and address how mixotrophy allows species to adapt to variable venting conditions. We measured the delta (super 15) N value of specific amino acids (AA) in chemosymbiotic invertebrate tissues and compare results to non-chemosynthetic related bivalve species (heterotrophic clam and mussel). We test a suite of delta (super 15) N (sub AA) trophic and microbial indices to elucidate the degree of bacterial influence versus particle feeding. Preliminary results reveal the AA-based trophic level equation, developed for marine photosynthetic food webs, suggests different isotopic parameters apply to chemosynthetic food webs. However, a parameter for estimating bacterial influence, Sigma V, does correlate with feeding mode. In addition, specific AAs (e.g., Proline and Lysine) show promise as sensitive proxies for chemoautotrophic influence and may be a tracer for chemosynthetic based production to the larger marine food web.