Lipid characteristics of hydrothermal vent organisms from 9°N, East Pacific Rise

Abstract

Abstract Lipid compositions are reported for three distinctive deep-sea hydrothermal vent invertebrate species collected around 9°N East Pacific Rise: Riftia pachyptila Jones, a vestimentiferan tubeworm; Bathymodiolus thermophilus Kenk and Wilson, a mussel; and Halice hesmonectes Martin et al. , an amphipod crustacean. The lipid compositions of all these organisms were dominated by components characteristic of diets based on bacteria, with only very minor contributions from carbon derived from the oceanic photic zone. In all the organisms studied, large abundances of n-7 fatty acids, polyunsaturated fatty acids with unsaturations separated by more than one methylene bond, and sterol distributions dominated by cholesterol were observed. Branched fatty acids were generally of low abundance, whereas polyunsaturated fatty acids separated by single methylene groups were either absent, as in the case of R. pachyptila , or in very low abundance, as in the case of B. thermophilus and H. hesmoncetes . Monounsaturated fatty acids were the most abundant component of R. pachyptila lipids, whereas non-methylene interrupted fatty acids were particularly abundant in the lipids of B. thermophilus (up to 450f total fatty acids). The lipids of H. hesmonectes were dominated by storage lipids (e.g. wax esters). Stable carbon isotope analyses of individual sterols from the organisms examined allow specific sources to be proposed for these biochemicals. The δ 13 C values of sterols from R. pachyptila were consistent with de novo biosynthesis, whereas that of cholesterol from B. thermophilus corresponded to that from marine phytoplankton. The δ 13 C values of sterols from H. hesmonectes fell into two different groups and suggest that at least two distinct sources of sterols are available to these crustacea in the vent ecosystem, one of which derives from phytoplankton. Overall, the combination of the interpretation of lipid structure and distribution with compound specific isotope analyses can lead to valuable insights into trophic relationships within the deep-sea hydrothermal ecosystem.