Beaufort Sea Zooplankton Communities 2010-14 and Relation to Hydrography

Zooplankton are important trophic links, yet are poorly characterized in the Beaufort Sea. Epipelagic zooplankton were sampled along across-shelf transects from Point Barrow to the Mackenzie River during August and September from 2010-14 as part of an interdisciplinary effort to characterize the biology of the Beaufort Sea. Seven copepod taxa dominated community abundance and biomass during all surveys: Calanus glacialis, Calanus hyperboreus, Metridia longa, Oithona similis, Triconia borealis, Microcalanus pygmaeus, and Pseudocalanus spp. Despite the dominance of these seven taxa, distinct faunal groupings associated with hydrographic characteristics were identified. The western Beaufort exhibited highest abundances of Pacific-derived taxa (e.g., Neocalanus spp.), demonstrating the hydrographic connectivity between the subarctic Pacific, the Chukchi Sea, and the Beaufort Sea. In contrast, the central and eastern Beaufort were more traditionally Arctic in faunal character, with the influence of the Chukchi Sea and Pacific-derived waters increasingly weakened towards the Mackenzie River. The eastern Beaufort in the vicinity of the Mackenzie River hosted markedly different communities in 2013 and 2014, reflecting the different freshwater signals observed during each survey. In 2013 we observed a strong freshwater signal, which resulted in extreme across-shelf faunal gradients and a nearshore community characterized by cladocerans, rotifers, and euryhaline copepod species. In 2014 euryhaline taxa were largely absent, reflecting the weak freshwater signal during the survey. Our work demonstrates the influence of hydrographic features on zooplankton community composition, allows comparisons with historical datasets spanning over 60 years, and provides a contemporary benchmark for Beaufort Sea zooplankton communities from which future change may be assessed.