Biogeochemistry and trophic structure of a cold seep ecosystem, offshore Krishna-Godavari basin (east coast of India)

Abstract

Active cold seep sites associated with shallow gas hydrates were recently reported from Krishna-Godavari (K-G) basin, off east coast of India. Benthic fauna including chemosymbiotic bivalves (genera Bathymodiolus, Acharax, Conchocele), polychaetes (genus Sclerolinum), and heterotrophs (gastropods: Provannidae family; squat lobster: Munidopsidae/Galatheidae; Goose barnacle: genus Neolepas; Brittle star: genus Amphiodia) were sampled from the cold seep locations. Here, we present the first δ13C and δ15N data sets of the soft tissues extracted from the organisms along with the sediment pore fluid composition. The isotope ratios of the soft tissues provide a glimpse of the potential food sources for the cold seep organisms and the trophic structure of the ecosystem. The δ13C values suggest the dependence of the Bathymodiolus on methanotrophic symbionts, whereas Acharax, Conchocele, and Sclerolinum show the tell-tale signature of the thiotrophic pathways. In contrast, the heterotrophic benthic fauna shows a wide range of δ13C values, a signature of a variety of carbon sources. The δ15N values of the studied organisms also show a broad range (−1 to +9 ‰) indicating variable food sources as well as variable nitrogen assimilation pathways followed by various symbionts.