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

Emmelie K. L. Åström*, Michael L. Carroll, Arunima Sen, Helge Niemann, William G. Ambrose, Moritz F. Lehmann, JoLynn Carroll

*Corresponding author:

ABSTRACT: 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, Frenulata (up to 32120 ind. m–2), and thyasirid bivalves, Mendicula cf. pygmaea (up to 4770 ind. m–2). We detected low δ13C signatures in chemosymbiotic polychaetes and in 3 species of omnivorous/predatory polychaetes. These δ13C signatures indicate the input of chemosynthesis-based carbon (CBC) into the food web. Applying a 2-source mixing model, we demonstrate that 28–41% of the nutrition of non-chemosymbiotic polychaetes originates from CBC. We also document 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.