ABSTRACT. Infaunal and epifaunal mollusks of the northeastern Chukchi Sea were sampled and 139 rnolluscan taxa were identified. The pattern of spatial distribution of molluscan species was determined by cluster analysis, which resulted in six infaunal and five epifaunal station groups. Species characterizing various faunal groups are defined. Stepwise multiple discriminant analysis was applied to correlate benthic biological associations with environmental variables. Delineation of infaunal groups was mainly due to percentage of Sand and bottom salinity, while epifaunal groups were separated by percent grave1 and bottom temperature. An increase in abundance and biomass of infaunal mollusks occurred adjacent to and north and northwest of an identified bottom front between the Bering Shelf and Resident Chukchi Water and Alaska Coastal Water. Epifaunal molluscan abundance and biomass were highest near the Coast. Mollusks, especially smaller species and the juvenile stages of larger species, represent a food resource for bottom-feeding predators in the study area.
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.
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