Advection and in situ processes as drivers of change for the abundance of large zooplankton taxa in the Chukchi Sea

Abstract

The Chukchi Sea has recently experienced increased water temperatures, increased advection of water from the Bering Sea, declines in sea-ice concentration, and shorter periods of ice coverage. These physical changes are expected to impact trophic food-webs and ecosystem attributes. In this study, a series of research surveys were conducted in the summers of 2011–2015 to characterize the physical environment and its relation to the abundance of large zooplankton. Large zooplankton are key prey for many higher trophic level organisms including seabirds, marine mammals, and fishes. Yearly advection from the Bering Sea influenced the adult large zooplankton abundance, but this influence was less apparent in the earlier development stages. Known development times of stages of zooplankton, along with their location within the study area, suggested that a fraction of the zooplankton standing stock was the result of local production. Decreased advection and later ice retreat resulted in higher abundances of the lipid-rich copepod Calanus glacialis. Warmer conditions with increased advection from the Bering Sea resulted in higher abundances of euphausiids. Warming, sea-ice melting, and increases in transport of Bering Sea water and plankton into the Chukchi Sea are ongoing, and changes in food-web structure are likely to result.