Biogeography of epibenthic assemblages in the central Beaufort Sea

Benthic communities change drastically in both biomass and community structure with increasing water depth on a global scale, attributed to a combination of food supply, environmental drivers, as well as physiological and competitive capacities. In the Arctic, benthic biogeographic patterns are additionally thought to be a result of the region's glaciation history. Here, we investigate gross epibenthic biomass and assemblage structure turnover with water mass from coastal to bathyal depths from 136 beam trawl samples collected in the Beaufort Sea. We test whether Pacific Boreal Arctic species have their core distribution in shelf water masses while Atlantic Boreal Arctic species have wider depth ranges. Gross biomass estimates differed statistically among water masses, with high values mostly under the influences of the Polar Mixed Layer and Arctic Halocline (outer shelf and upper slope, respectively). Stations in the Coastal Zone and Canada Basin Deep Water had the lowest biomass. Epibenthic assemblages also differed significantly among water masses, with high taxon richness in shelf water masses that decreased considerably with depth. Biomass of benthic taxa with Pacific Boreal Arctic affinity was essentially limited to the shelf, while Atlantic Boreal Arctic taxa occurred across a broad depth range, though their biomass increased in deeper water masses for mollusks and echinoderms, but not for decapods/isopods. Our results confirm earlier evidence of a strong Atlantic-Arctic deep-water connectivity reaching into the Pacific Arctic region and suggest new arrivals of species from the boreal Pacific are likely to settle on Pacific Arctic shelves, but are unlikely to invade continental slope and basin waters in the foreseeable future.