Trophic Dynamics of Calanus hyperboreus in the Pacific Arctic Ocean

Abstract

The zooplankton community composition in the Pacific Arctic Ocean depends heavily on the sea ice and hydrodynamic conditions. The calanoid copepod Calanus hyperboreus is a dominant Arctic zooplankton, but its diet sources in the Pacific Arctic are unclear. C. hyperboreus individuals were collected in the northern Chukchi Sea (NCS) and the northern-East Siberian Sea (NESS), which display contrasting chlorophyll abundance and sea ice concentration in summer 2018. Nitrogen isotopes of individual amino acid and fatty acid compositions were measured to determine its trophic level (TL) and dominant diet. C. hyperboreus collected in the NCS had higher TL values (3.0 ± 0.2) and a relatively low proportion of C20:5(n-3). In the NESS, C. hyperboreus had lower TL values (2.7 ± 0.2) and a larger percentage of C20:5(n-3), suggesting a greater proportion of diatoms in its diet. Spatial TL variations of C. hyperboreus between the NCS and NESS may be caused by variations in phytoplankton composition (micro-phytoplankton vs. nano- and picophytoplankton) as a result of surface seawater stratification triggered by the inflow of sea ice meltwater as well as summer Bering Sea water through the Bering Strait. These results suggest that the filter-feeding copepod C. hyperboreus could be a useful indicator to understand trophic dynamics in zooplankton food web.