Chemosynthesis-influenced trophic relationships and community structure at Barents Sea cold seeps

Abstract

Cold seeps where methane and other reduced compounds emerge at the seabed can form the basis of chemosynthetic habitats and seafloor communities. We examined methane cold-seeps at three distinct locations in the Barents Sea in order to characterize the community and trophic structures. The seeps supported high densities (up to 3212 individuals 0.1 m−2 ) of chemosymbiotic polychaetes (Siboglinidae, Frenulata), and thyasirid bivalves, Mendicula cf. pygmaea (up to 477 individuals 0.1 m−2 ). These two taxa represent the defining fauna of cold seeps at these locations. Stable carbon isotopic analysis showed that chemosymbiotic polychaetes generally displayed a low δ 13C signature (δ 13C = -38.2h and -47.1h), suggesting syntrophy and chemosynthesis-based nutrition for these taxa. Furthermore, we detected low δ 13C signatures (-26.1h to -31.4 h) in three species of non-chemosymbiotic polychaetes, indicating input of chemosynthesis-based carbon derived from seeping hydrocarbons. A 2-source mixing model revealed that up to 28-41 % of the nutrition of these polychaetes originates from chemosynthesis-based carbon. We documented large community variations and small-scale variability within and between the investigated seeps. Moreover, we observed aggregations of heterotrophic macro, - and megafauna associated with characteristic seep features such as microbial mats, carbonate outcrops and chemosymbiotic worm-tufts. Cold seeps in the Barents Sea are unique habitats with a potentially high relevance for the Arctic-Barents Sea ecosystem, with increased habitat complexity and three-dimensional structure to seafloor systems. Seeping hydrocarbons and associated chemoautotrophy add a supplementary energy source to benthic habitats at Barents Sea seeps, challenging the paradigm of Arctic ecosystems as fueled solely by photosynthesis and benthic-pelagic coupling.