Chemosynthesis influences food web and community structure in high-Arctic benthos

Cold seeps are locations where seafloor communities are influenced by the seepage of methane and other reduced compounds from the seabed.We examined macro-infaunal benthos through community analysis and trophic structure using stable isotope analysis at 3 seep locations in the Barents Sea.These seeps were characterized by high densities of the chemosymbiotic polychaetes Siboglinidae, clade Frenulata (up to 32 120 ind.m -2 ), and thyasirid bivalves, Mendicula cf.pygmaea (up to 4770 ind.m -2 ).We detected low δ 13 C signatures in chemosymbiotic polychaetes and in 3 species of omnivorous/predatory polychaetes.These δ 13 C signatures indicate the input of chemosynthesis-based carbon (CBC) into the food web.Applying a 2-source mixing model, we demonstrated that 28-41% of the nutrition of non-chemosymbiotic polychaetes originates from CBC.We also documented large community variations and small-scale variability within and among the investigated seeps, showing that the impact of seepage on faunal community structure transcends geographic boundaries within the Barents Sea.Moreover, aggregations of heterotrophic macro-and megafauna associated with characteristic seep features (microbial mats, carbonate outcrops, and chemosymbiotic worm-tufts) add 3-dimensional structure and habitat complexity to the seafloor.Cold seeps contribute to the hydrocarbon-derived chemoautotrophy component of these ecosystems and to habitat complexity.These characteristics make the cold seeps of potential high ecological relevance in the functioning of the larger Arctic-Barents Sea ecosystem.