Abstract
In the coastal waters of the Black Sea near Sevastopol, a gradual temperature elevation and an increase in anthropogenic pressure since the early 2000s have caused significant structural and functional changes in phytoplankton. Currently, there is a significant decrease in the contribution of small diatom species (Skeletonema sp. and Chaetoceros socialis H.S.Lauder as well as coccolithophorids Emiliania huxleyi (Lohmann) W.W.Hay and H.P.Mohler) to the total phytoplankton biomass in these waters. Previously these species caused regular weak blooms. In the warm periods (from May to October), during which the main phytoplankton biomass is formed, large diatom species Pseudosolenia calcar-avis (Schultze) B.G.Sundström, 1986, Proboscia alata (Brightwell) Sundström and dinoflagellates predominate. Therefore, the maximum values of the phytoplankton community’s specific growth rate are about two times lower than in the preceding periods and do not exceed 1.10–1.40 day−1. There was also a decrease observed in the microzooplankton grazing rate, which, during the year, was no higher than 0.70–1.20 day−1. This is primarily conditioned by the increased role of large algae in phytoplankton, which means a decline in nutrition quality for microzooplankton. As a result of the joint influence of nutrition quality and water pollution, the relative share of net primary production consumed by microzooplankton in the warm periods of the year averaged only 32%, which is two times lower than the average values generally accepted for marine ecosystems. This means that the transfer of matter and energy from phytoplankton to higher trophic levels is significantly decreased.
Highlights
An assessment of the current state and possible evolution path of marine ecosystems within the conditions of global climate changes and constantly increasing anthropogenic pressures is one of the main ecological problems globally
The maximum values of phytoplankton biomass are observed as a rule in late summer and early autumn, when the majority of phytoplankton is constituted of large diatom species
Summarizing the above, we can conclude that in 2020, as a result of temperature increase and growing anthropogenic water pollution, a significant restructuring of the species composition and size structure of phytoplankton occurred in the studied areas of the Black Sea
Summary
An assessment of the current state and possible evolution path of marine ecosystems within the conditions of global climate changes and constantly increasing anthropogenic pressures is one of the main ecological problems globally. Due to climatic changes, seawater temperature has globally increased by approximately 1 ◦C [1]. From the middle of the 1990 s, within the surface layer of the Black Sea deep-water areas, temperature changes have been characterized by a positive trend [2]. As a result of temperature stratification increasing in the water column, nutrient supply from the depths to the photosynthesis zone gradually decreases [3]. In the coastal waters in the Crimean Peninsula area, the multiannual unidirectional positive trend in the water temperature of the surface layer has been observed [4]. A gradual increase in the water temperature of the surface layer since the early 2000 s was detected in the coastal waters of the Black Sea
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