Zooplankton of the Laptev Sea: Is the “Effect of the Continental Slope” Manifested in the Distribution, Feeding Activity and Grazing Impact on Phytoplankton?

Mesozooplankton composition, distribution, and grazing in the areas of the continental slope, outer shelf and deep basin of the Laptev Sea were studied. Data were obtained in August-September 2018 during the cruise # 72 of the RV Akademik Mstislav Keldysh at two quasi-meridional sections. Zooplankton biomass (DW) in the 0-bottom layer increased with depth from 3-5 g ∙ m on the shelf to 9-17 g ∙ m above the slope and 12-17 g ∙ m in deep-water areas. Over the shelf and slope, the share of Calanus glacialis in the total biomass was 80% and 45%, and it decreased to 32% in the deep-water area while C. hyperboreus’ increased to 39%. Contrary to the present concept of an of increased plankton concentration “belt” over the continental slope, no increase in the total zooplankton biomass was found in this area. Difference in the timing of the seasonal ice retreat was significant for the development of the C. glacialis and had virtually no effect on the population dynamics of C. hyperboreus and Metridia longa. Daily rations through herbivory did not cover metabolic expenditures. Daily zooplankton grazing impact on phytoplankton of the size fraction > 3 µm was 0.4-2% of phytoplankton biomass on the shelf, 7-10% above the slope, and 1.5-6% in the deep-water area.