Depth-stratified community structure of Beaufort Sea slope zooplankton and its relations to water masses

Abstract

Depth-stratified samples were collected along the Beaufort Sea slope during August and September 2012-2014 to characterize the vertical structure of zooplankton communities from 0 to 1000m. We documented 95 holoplanktonic categories (88 species, 5 genera, 1 order and 1 phylum); greatest diversity was observed in the copepods (51 species and 1 genus), followed by the cnidarians (11 species and 1 genus) and amphipods (7 species and 3 genera). Distinct communities were associated with the main water masses in the study region: The Polar Mixed Layer (PML; 0-50 m), Arctic Halocline Water (50-200m) and Atlantic Water (AW; 200-1000 m). Average abundance and biomass were highest in the PML (1230 ind.m-3 and 24.3mgDWm-3, respectively) and declined to a minimum in AW (22 ind.m-3 and 1.9 mgDWm-3, respectively). Copepods dominated in the PML, with Calanus species, Oithona similis, Metridia longa, Triconia borealis, Microcalanus pygmaeus and Pseudocalanus spp. contributing more than 80% of copepod abundance and biomass. Mesopelagic copepods were important contributors to the AW community, which exhibited the highest species richness. Community structure was highly correlated with salinity and depth. We report similar species composition but higherbiomass when compared with the interior basins, likely due to elevated coastal production.