Melnikov, V.V., V.N. Belokopytov & A.V. Masevich. (2024). Possible influence of deoxygenation on the distribution structure and trophic connections of cold-water zooplankton species and fishes of the Black Sea. Izvestiya Samarskogo Nauchnogo Centra Rossiskaya Akademii Nauk. 26(5):94-108.
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Melnikov, V.V., V.N. Belokopytov & A.V. Masevich
2024
Possible influence of deoxygenation on the distribution structure and trophic connections of cold-water zooplankton species and fishes of the Black Sea.
Izvestiya Samarskogo Nauchnogo Centra Rossiskaya Akademii Nauk
26(5):94-108.
Publication
The article presents the author's analysis of the possible effect of deoxygenation on the distribution structure and trophic relationships of cold-water zooplankton and fish of the Black Sea. A systematic generalization of the published data showed that over the past 60 years, intensive deoxygenation of the depths has raised the lower boundary of the cold-water zooplankton vertical distribution of by almost 50 m up. This is the boundary between oxic and anoxic waters, corresponding to the upper boundary of the suboxic layer (O2 10 microns, &sit = 15.8), where cold-water zooplankton species descend daily during the day, reducing energy costs, hiding from fish, and where some of them are in diapause in the warm season of year. In the preeutrophication period (in the 1960s and 1980s, when there was good aeration of the water column) these organisms sank daily to the 120-130 m depth, and the Black Sea sprat (living at depths up to 100 m) could only feed on them during their daily vertical migrations: at this there was a lot of food, but there were few sprats. During the eutrophication period (1980-1990), when deoxygenation raised the lower limit of zooplankton accumulations in the entire deep-sea zone above 100 m, fish gained unrestricted access to deep-sea accumulations of forage zooplankton. Predators and prey appeared in the same water layer, and the sprat's food composition consisted of 100% large cold-water copepod Calanus euxinus Hulsemann, 1991. The abundance of feed led to the fact that the number of sprats in 1980-1990 increased by almost an order of magnitude, and their fat content became maximum. The eating of copepods led to the fact that, despite the abundance of phytoplankton during the eutrophication period, the number of fodder zooplankton began to decline rapidly. In the posteutrophication period, in conditions of a rapid decrease in the amount of oxygen in the depths of the sea, the tendency to reduce stocks of forage plankton persisted until the appearance of the predatory ctenophore mnemiopsis, which in the period from 1988 to 1992 destroyed almost all life in the sea, including zooplankton, eggs and fish larvae. Thus, the authors of this study for the first time hypothesize that, along with the already described patterns of long-term changes in the Black Sea ecosystem under the influence of pollution, climate change, the appearance of invaders and overfishing, there is another (previously undescribed) factor: "choric" changes in the biological structure of the Black Sea water masses. The anoxic waters rise displace cold-water species to the surface. This not only affects their distribution and trophic relationships, but also creates prerequisites for their disappearance in the event of a further reduction in oxygen supply to the depths of the sea.
