Spatial variability of epibenthic communities on the Alaska Beaufort Shelf

Arctic marine epibenthos contribute significantly to the regional biomass, remineralization and redistribution of organic carbon, and are key elements of local food webs. The main purpose of this study was to describe the epibenthic invertebrate community on the Alaska Beaufort Shelf and identify links between community patterns and environmental drivers. Using a plumb-staff beam trawl, 71 stations were sampled between 13 and 220 m and from 145.09A degrees W to 155.25A degrees W along the shelf, in August/September of 2011. At each station, epibenthic taxonomic composition, abundance and biomass data were collected together with environmental data. Significant spatial variability in community composition and standing stock of the dominant taxa were observed along changes in depth and along-shelf position. The significant interaction between along-shelf position and depth helped define six geographic domains (two regions with three depth groups each). Shallow stations (< 25 m) were dominated by mobile crustaceans and had the lowest values in diversity indices and total number of taxa. Mid-depth stations (26-100 m) had the highest values in diversity indices and were dominated by mollusks, crustaceans and echinoderms. Deep stations (101-220 m) were mostly represented by echinoderms and crustaceans with intermediate diversity values but high abundance and biomass values. However, at constant depth ranges, there were very few similar representative taxa in the eastern and western regions. Also, a clear reduction in abundance and biomass along the shelf break was observed from west to east. The six most influential environmental drivers (sediment phaeopigments, bottom water salinity, bottom water temperature, sediment organic matter, bottom water pH and percent sand) explained up to 50 % of the variance in epibenthic community structure. Through this study, we learned that the epibenthic community on the Alaska Beaufort Shelf is diverse, spatially heterogeneous and can have high biomass and density. Also we show how these community assemblages and total epibenthic biomass are linked to spatial changes in the environment through changes in bottom water temperature, salinity, sediment grain size and proxies for food quantity and quality.