Characteristics of productivity for the Academy Bay (Okhotsk Sea)

The data on parameters of biological productivity measured in the Academy Bay in September 2020, as chlorophyll a concentration in the euphotic layer, primary production, phytoplankton and zooplankton biomass, and results of echo sounding at 200 kHz are presented. The primary production estimated by Zvalinsky model varied from 300 to 6050 mgC per m² per day. Diatoms with the biomass of 660–1220 mg/m³ dominated in phytoplankton, whereas Copepoda with the biomass ranged from 18 to 478 mg/m³ was the dominant zooplankton group. A discrepancy is noted between the measured net zooplankton biomass and thickness of the sound diffusion layer. The more productive area with the highest biomass of zooplankton was found in the northern Academy Bay enriched by nutrients transferred there from the Okhotsk Sea due to patterns of the estuarine circulation, but the thickest sound-diffusing layer was observed in the southern and central parts of the bay where it was presumably formed by shoals of juvenile fish rather than copepod aggregations. The feeding grounds of bowhead whales were located in the southern Academy Bay, too. This spatial misalignment of the feeding grounds with the highly productive area is explained by the hypothesis that juvenile fish may be important prey for whales, in addition to zooplankton.

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