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22Although knowledge of Arctic seas has increased tremendously in the past decade, benthic 23 diversity was investigated at regional scales only, and no attempt had been made to examine it 24 across the entire Arctic. We present a first pan-Arctic account of the species diversity of the

Climate change and increased focus on resource development in Arctic Seas have fueled interest in the Chukchi Sea, yet few quantitative studies have been conducted on the larger, epifaunal component of seafloor communities, which serves important roles in sediment biogeochemical processes and provides a food source for fishes and marine mammals. Here we provide quantitative data on the present condition of benthic epifaunal abundance and biomass from the Chukchi shelf and examine the influence of environmental variables on epifaunal communities. We . Overall, abundance and biomass were dominated by echinoderms (66 and 45%, respectively) and crustaceans (17 and 31%, respectively). The ophiuroid Ophiura sarsi and the snow crab Chionoecetes opilio overwhelmingly dominated abundance and biomass. The holothurian Myriotrochus rinkii also occurred in large numbers, and the urchin Strongylocentrotus pallidus was another major contributor to biomass. A total of 165 taxa (mostly species) were identified; the highest numbers were Mollusca (45) and Crustacea (33). Cluster analysis identified 6 distinct groups plus 6 unique stations with 54 to 88% between-cluster dissimilarity, with separation based largely on substrate type and latitude. Water mass characteristics and indices of food availability appeared less influential in generating the observed composition, abundance and biomass patterns. Comparisons with previous studies suggested an increase in overall epibenthic biomass since 1976, including an increase in the biomass of C. opilio.

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Based on data from the Weddell Sea in the Atlantic sector of the Southern Ocean, the total number of macrozoobenthic species was estimated for the entire Antarctic shelf using species-accumulation methods, jack-knife estimators, and Incidence-based Coverage Estimators of species richness. Ranging between 11 000 and 17 000 expected species, Antarctica seems to have an intermediate species richness when compared to other selected tropical, temperate or Arctic habitats.

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