Benthic communities at high-Arctic cold seeps: Faunal response to methane seepage in Svalbard

Cold seeps are chemosynthetic habitats found in both deep sea and shallow ocean-shelves worldwide, including the polar regions. At seeps, hydrocarbons, sulfide, and other reduced compounds emerge from the seafloor, providing energy to fuel chemoautotrophic production. Microbial assemblages, supported by the oxidation and reduction of gases and fluids, form the base of a food web composing unique and specialized cold-seep ecosystems. Several methane cold seeps have been documented in the high-Arctic, offshore Svalbard and in the Barents Sea, within the depth range of 85-1200 m. The widespread seabed gas seepage in these areas can be a strong environmental driver, influencing the local seafloor conditions and biosphere, including benthic community structure and ecosystem function. The primary aim of this doctoral thesis has been to describe the current seep-associated communities and habitats located on the shelf of western Svalbard and in the Barents Sea. This included determining the ecological structure, diversity and food web interactions of macrofaunal assemblages at high-Arctic cold seeps, describing how they compare with conventional non-seep communities, and examining the interaction between seep and non-seep communities where they co-occur. Key findings from the study are: 1) Cold seeps have a strong, localized effect over small spatial scales, supporting dense communities of small chemosymbiotic worms that play a fundamental role in structuring the seabed animal community 2) Cold seeps are identified as focal areas for the biosphere, providing heterogeneous substrates and additional food resources independent of photosynthetic sources from the surface ocean, resulting in animal aggregations at these habitats. 3) Methane-derived carbon is incorporated into the food web of the Barents Sea ecosystem. 4) The discovery of two new species of methane-associated bivalves at Svalbard cold seeps. Cold seeps in the Arctic are of high ecological importance and methane is a key environmental driver of the biological system. Characteristic seep features, such as methane derived carbonate rocks and chemosymbiotic worm tufts, add complexity and 3D structure to the otherwise relatively flat and barren seafloor. Cold seeps provide shelter and substrate to both infauna and sessile organisms at seafloor, and to larger motile animals. Furthermore, cold seeps and seabed methane emissions add a supplementary energy source into the Arctic ecosystem. By combining results o