Distribution and feeding of dominant zooplankton species under autumn coccolithophorid development in the eastern part of the Barents sea

Abstract

Studies of zooplankton spatial distribution and feeding were conducted in the eastern part of the Barents Sea in early October 2014. The study period was characterized by positive anomalies of the water temperature in the upper mixed layer and by the dominance of coccolithophorids in phytoplankton. The scale of spatial variability of zooplankton biomass (6.143.3 mg DW m-3) over the 30,000 km2 investigated area was comparable to the range of interannual variation of zooplankton biomass in the Barents Sea. Calanus finmarchicus and Metridia longa dominated in the zooplankton community. The spatial distribution of C. finmarchicus was correlated with the depth: at the stations, where the depth exceeded 250 m, the biomass was threefold higher than that at the shallower stations. Both species performed diel vertical migrations ascending to the upper 50 m layer during night and actively consuming there coccolithophorids and tintinnids Acanthostomella norvegica. Taking into account the contribution of tintinnids, the amount of assimilated organic carbon in C. finmarchicus CV, CIV and M. longa CV, CIV was 2.6, 8.3 and 3.5, 4.9% of body carbon content, respectively, and compensated therefore the metabolic costs. Grazing impact on the autotrophic phytoplankton by the populations of C. finmarchicus and M. longa did not exceed 5% of its biomass and was preconditioned by the abundance and the feeding activity of migrating copepods.