Arctic cold seeps in marine methane hydrate environments: impacts on shelf macrobenthic community structure offshore Svalbard

Cold seeps are locations where hydrocarbons emanate from the seabed, fueling chemoautotrophic production that may support macrofaunal communities via chemosymbiosis or trophic inter actions. The recent discovery of offshore sub-seabed gas reservoirs and venting methane at the seabed in Svalbard (75 to 79 degrees N) provides the context to examine the influence of cold seeps on macrofaunal community structure in the high-Arctic. We compared benthic macrofaunal community structure from cold-seep environments and paired control stations from 3 regionally distinct areas along the western Svalbard margin and the western Barents Sea. Specialized seep-related polychaetes (e.g. siboglinid tubeworms) were found at seep stations in the Barents Sea in high densities (up to 7272 ind. m(-2)). The presence of obligate seep-associated faunal taxa demonstrates that chemoautotrophic production, fueled by methane and sulfur, influences benthic communities at these seeps. Further, total biomass was significantly higher at seep-impacted stations compared to controls (mean = 20.7 vs. 9.8 g wet weight sample(-1)), regardless of region. Four methane seep-influenced samples showed clear indications of seep impact, with reduced diversity and with a few species dominating, compared to controls. Our results demonstrate that the effect of methane seeps on the Svalbard shelf benthic community are highly localized (i.e. meter scale), reflecting strong gradients associated with the point-source impacts of individual seeps. Regional differences and the restricted spatial extent of focused emissions likely drive the observed complexity and heterogeneity at Svalbard cold seeps. These results provide key base-line observations in a high-Arctic location that is likely to be influenced by warming sea temperatures, which may lead to increased seabed methane release.