Biomass and production of net zooplankton in the Bering Sea

Abstract

Total biomass and production are evaluated for taxonomic groups of zooplankton sampled with Juday net (mesh size 0.168 mm) from the 0-200 m layer in the Bering Sea in 1986-2018. The annual mean stock of zooplankton is assessed as 245.1 . 106 t WW, or by taxonomic groups: copepods — 135.0 . 106 t (55.1 %), chaetognaths — 664.4 . 106 t (26.3 %), euphausiids — 30.8 . . 106 t (10.8 %), medusas — 7.9 . 106 t (3.2 %), and hyperiids — 7.0 . 106 t (2.9 %). The gross annual yield is estimated as 1378.6 . 106 t for copepods (P/B = 9.3), 422.5 . 106 t for chaetognaths (P/B = 6.0), 212.5 . 106 t for euphausiids (P/B = 9.0), 132.4 . 106 t for net medusas (P/B = 16.7), and 90.9 . 106 t for hyperiids (P/B = 12.3). The total annual yield of 2281.9 . 106 t, on average, was formed as a sum of 107.4 . 106 t produced in winter (P/B = 1.0), 889.6 . 106 t — in spring (P/B = 2.4), 755.2 . 106 t — in summer (P/B = 2.8), and 529.6 . 106 t — in autumn (P/B = 2.2). This annual yield was produced mostly by non-predatory zooplankton (1613.8 . 106 t), but also by predatory zooplankton (668.1 . 106 t). Mean annual P/B-ratio for the entire zooplankton in the Bering Sea was 8.5 that was in 1.4 times lower than in the Okhotsk Sea (P/B = 11.8), mainly because of predominance of less productive Copepoda species.