Pacific and Atlantic water influence on the Beaufort Sea slope tracked by epifaunal invertebrate biogeography

As an interior Arctic sea with a narrow shelf and a steep slope, the US Beaufort Sea is influenced by complex vertical and horizontal domains of water masses and current regimes. The benthic invertebrates inhabiting that area form communities that reflect the long-term (year to decadal) environmental conditions and waters mass source. During six expeditions over five years, we deployed plumb-staff beam trawls to collect epifauna invertebrates at >150 locations spanning the shelf and slope to 1000 m and across the primary water masses of the region (as defined by T/S). The >250 species sampled in this effort are dominated in species richness by crustaceans and gastropods, and in abundance and biomass by echinoderms and crustaceans, with proportional variations across water depths. We find strong turnover in species and/or community composition with water depth, and moderate shifts along the west-east axis. Depth-related species/community shifts are gradual, but most pronounced around the 20 m isobaths, at the shelf break (between 100 and 200 m) and between 350 and 500 m. Inshore of ~20 m, the dynamic environment (ice gouging, variable salinity) results in a species-poor community. At locations deeper than ~350 m, communities increasingly include species common in the Atlantic-influenced Arctic and Atlantic-boreal regions, roughly matching the transition from Pacific-origin to Atlantic-origin waters. We conclude that benthic community distribution can delineate boundaries in hydrographic conditions that are characteristic of different water mass types that reside on the shelf and slope of the Beaufort Sea.