TROPHODYNAMICS OF MARINE ORGANISMS IN THE EPIPELAGIC LAYER OF THE OKHOTSK SEA IN 2000S

Abstract

New data on matter and energy transfer between major components of the Okhotsk Sea ecosystem are obtained on the base of trophodynamic modeling, taking into consideration their production and food consumption rates. The main trophodynamic relationships in the pelagic and bottom communities are determined from observations on zooplankton and nekton abundance, organic carbon content, food habits of marine organisms, and their isotope composition in 2000–2014. The total zooplankton production in the entire Okhotsk Sea in these years is assessed as 2616 . 106 t in raw weight, including 2275 . 106 t for non-predatory plankton, and 341 . 106 t for predatory plankton. So high total production of zooplankton is conditioned by favorable environmental conditions and dominance of high-productive species. Taking into account the rate of zooplankton consumption by predators, only 22.4 % of the total annual zooplankton production was consumed annually, with 16.2 % grazed by predatory plankton and 6.2 % by nekton. In carbon units, 831.0 . 106 tC was produced annually in the Okhotsk Sea at the first trophic level, 177.4 . 106 tC at the second trophic level, 18.1 . 106 tC at the third trophic level, 0.74 . 106 tC at the fourth trophic level, and 0.016 . 106 tC at the fifth trophic level. Pelagic nekton consumed 159 . 106 tC annually. The nekton prey included 85.5 % of zooplankton, 12.8 % of nekton, and 1.7 % of zoobenthos, by biomass. The main part of zooplankton consumed by nekton (50.7 %) was grazed by walleye pollock, 18.9 % by herring, 16.6 % by squids, 7.6 % by capelin, 5.3 % by deep-sea smelt, and 0.9 % by salmons. The total annual production of organisms in the epipelagic layer of the Okhotsk Sea exceeded 109 tons of C (1027.4 . 106 tC/year equal to the biomass of 17.85 . 109 t in wet weight). Primary production is estimated as 67.60 % of gross production in carbon units, microheterotrophic organisms produce 13.30 %, dominant zooplankton groups — 18.60 % (copepods 11.40 %, euphausiids 5.50 %, sagittas 1.20 %, and hyperiids 0.50 %), the portion of nekton production is estimated as 0.13 % of gross production.