Nº 1 (2024)

Based on the data of complex environmental studies, which have been regularly carried out at six standard stations of the Rybinsk Reservoir since the middle of the 20th century, the orientation of changes in the elements of the reservoir ecosystem associated with global climatic events has been analyzed. During the period of climate warming, which began in 1977 and continues into the 21st century, the air temperature in the warm season increased by 0.9°C, the water temperature by 1.4°C, the average annual inflow by 7.5%, and the duration of the ice-free period by two weeks. An increase in electrical conductivity and color of water, a decrease in transparency were noted. With significant interannual variations in biological characteristics, in the XXI century, the number of bacterioplankton increased by 1.7 times, and bacterial production doubled. Chlorophyll content increased by 1.4 times and values >15 µg/L reflecting the eutrophic state of the reservoir began to be observed more often. In the biomass of phytoplankton, the proportion of small cell forms increased. The total abundance of phytoplankton increased due to the development of cyanobacteria, which form a long summer maximum in the seasonal dynamics of the community. The increase in water mineralization promoted the progressive spread of alien brackish-water algae. Biomass of zooplankton increased by 2.5 times. An increase in the abundance of crustaceans (Cladocerans, by 1.6 times; Copepods, by 1.9 times) caused a change in the structure of zooplankton and the formation of a strong late summer peak of biomass. The intensification of hydrobiological processes was clearly manifested after the abnormally hot 2010, the conditions of which not only stimulated the development of plankton communities, but also but also caused the formation of oxygen deficiency in the bottom layers. Warming has significantly transformed the ecosystem of the Rybinsk Reservoir, intensified eutrophication processes and worsened water quality. Changes in hydrometeorological characteristics have gone beyond the mild scenario of climate warming.

The long-term (2001–2020) data of the primary production and abundance of phytoplankton (according to the concentration of chlorophyll a) in the Vistula Lagoon under significant ecosystem changes were analyzed. The long-term dynamics was characterized by an increase in primary production to a hypertrophic level (>450 g C/(m² · year) in 2006–2010. After the intensive development of the bivalve filter-feeding mollusk Rangia cuneata, primary production in 2011–2020 remained at the hypertrophic level, despite significant changes in the structure and abundance of phytoplankton. Average annual primary production in 2001–2020 was 60% higher than in 1974–1976. Primary production exceeds the mineralization of organic matter in water by 60%, which leads to secondary eutrophication of the Vistula Lagoon and pollution of the Baltic Sea.

The results of summer studies of phyto- and zooplankton in aquatic systems of the technogenic origin are presented. There are low species richness and a significant range of the quantitative indicators of aquatic organisms. The change of the main structure-forming taxa in the pH gradient is shown. Environmental factors that determine the composition and structure of plankton communities have been identified.

The results of phytoplankton biomass study in different regions of the Lake Baikal according to data of 15 expeditions from 1994 to 2013 are presented in the paper. Spatial distribution and interannual dynamics of biomass of phytoplankton in all three throughs of the lake are analyzed. The general biomass of phytoplankton during late Summer is not high. The multiyear average phytoplankton biomass equals 169 ± 5 mg/m³ for open waters of the lake. It is distributed relatively uniformly around the Southern Baikal. Higher multiyear average values are along Eastern shore in the Middle and Northern Baikal. The late summer phytoplankton biomass in Southern and Middle throughs does not differ. Average multiyear biomass of phytoplankton of Northern through is accurately lower than one for two other throws. There is no increase of biomass for any region of the lake demonstrated. The relations of general biomass of phytoplankton with water temperatures are very slight.

For the first time, the change of phytoplankton along the length of the Ural River from Verkhneuralsk to Orenburg (on a site of more than 1000 km) was studied. A powerful eutrophying effect of Magnitogorsk on the river for more than 150 km has been revealed. It manifests itself in the fact that the phytoplankton biomass in this area increases greatly, averaging about 15 mg/ l (with the dominance of cyanobacteria Microcystis aeruginosa), and the species diversity index (Shannon index), on the contrary, reaches extremely low values of 0.25. This indicates a significant oppression of the plankton community and deterioration of water quality. In the Ural River above this site (from Verkhneuralsk to Magnitogorsk reservoir), as well as below it (from Orsk to Orenburg), phytoplankton indicators correspond to the usual values: biomass is 1.6–1.7 mg/l, Shannon index is 3.3–3.5 (on average for each site). This suggests that the conditions for the existence of plankton in the upper and lower areas are favorable. At the same time, the sites differ in the composition of algae: the first is dominated by diatoms, the second is predominantly green. Perhaps this is due to geographical factors: in the north, the Urals flows in the forest-steppe zone, and in the south it passes into the steppe.

Pulse feeding and growth of the Black Sea strain of dinof lagellates Oxyrrhis marina (Dujardin, 1841) (OXY–IBSS), equivalent spherical diameter (ESD) (23.5 ± 3.1 mm) have been studied under experimental conditions simulating phytoplankton blooms. Microalgae Phaeodactylum tricornutum (P, ESD 3.4 ±0.3 mm), Isochrysis galbana (I, ESD 3.7 ± 0.4 mm), Tetraselmis suecica (T, ESD 6.1 ± 0.9 mm), and Rhodomonas salina (R, 7.4 ± 0.7 µm) were used as food objects in a one-component and three-component suspensions. Microalgae concentrations (~10⁶ cells/mL for T and R; up to ~4 × 10⁶ cells/mL for P and I) were chosen to ensure their equal total carbon biomass ~0.02 mg C/mL in the food mixtures at the beginning of the experiment. Under ad libitum conditions, the maximum clearance rates of the OXY–IBSS reached 0.1–0.5 mL ind./day, and the grazing rate of microalgae was 34–44 cells/(ind h) for P and I, and 2–11 cells/(ind. h) for R and T, respectively. The grazing rate of microalgae in carbon units was significantly higher when feeding on I (3.9 ng C/(ind. day)) and significantly less when fed with a mixture of microalgae TRP (1.5 ng C/(ind. day)). Maximum abundance of OXY–IBSS, achieved within 3 or 4 days (by the time the microalgae concentration decreased below threshold), varied from 19 × 10³ ind./mL (P) to 43 × 10³ ind./mL (I). In the absence of food, dinof lagellates O. marina turned to cannibalism, and within 4 days the oscillating f luctuations (within 50%) in their number took place. Although the specific population growth rate (m, day-1) of OXY–IBSS was higher when feeding on small cells (~2 days^–1 on I), the gross growth efficiency (GGE) of OXY–IBSS was significantly higher when fed on large (T and R) microalgae (26–29% vs. 14–15%). At lower daily rations (DRs) when fed with the mixture TRP, the GGE of OXY–IBSS was significantly higher (41%) when compared to other nutritional conditions. The feeding strategy of opportunistic predator O. marina on diverse (in terms of size and chemotaxonomic characteristics) mixtures of prey lay in a f lexible choice between high specific population growth rate, or high gross growth efficiency, that obviously gives the populations of this species the advantages over other protists under conditions of the pulsed phytoplankton blooms.

The taxonomic structure and spatial distribution of the late-summer zooplankton in the Volga River from the upper Ivankovo reservoir to Volga Delta near Astrakhan during the period 2020–2021 were studied. Zooplankton biomass in the most of the Volga reservoirs was dominated by cladoceran Daphnia galeata and copepod Mesocyclops leuckarti (up to 45–84%). However different dominant species were observed in the Volgograd reservoir. Cladocerans Chydorus sphaericus and Bosmina cf. longispina formed there up to 43% of the total zooplankton biomass. Rotifers and Ponto-Caspian copepod Heteroscope caspian are dominated in the Volga River below the dam of the Volzhskaya hydropower plant (56% and 18% of the total zooplankton biomass respectively). Among the invasive species, most abundant are East Asian copepod Thermocyclops taihokuensis (up to 230 thsd. ind./m³ and locally >90% of the total biomass) and North American copepod Acanthocyclops americanus (up to 86 thsd. ind./m³ and >35% of the total biomass). The maximum abundance of the zooplankton (0.8–1.6 g/m³) was observed in the Upper Volga reservoirs while the minimum abundance (0.1–0.2 g/m³) – in the Lower Volga. The maximum abundance of zooplankton (0.8–3.3 g/m³) was recorded in the mouth areas of the reservoir tributaries, while the minimum abundance (0.1–1.4 g/m³) – in the pelagic zone of the reservoirs. A decrease in the zooplankton community biomass from Upper to Lower Volga was observed in all biotopes. A negative correlation between the community abundance and daily water inflow into the reservoirs and a positive correlation between the community abundance and water temperature were revealed. Long-term variations in zooplankton biomass and their relationship with water body trophic state, thermal and oxygen regimes were discussed.

The zooplankton of the caught floodplain lakes of the Middle Ob, located at various distances from the main riverbeds, was studied. It is shown that the development of the summer complex of zooplankton in floodplain lakes begins simultaneously with the passage of the flood; a significant diversity of species and the largest biomass increase in them in the summer months. The more often the floodplain lakes is filled with hollow waters, the higher the species diversity and the calculated indicators of plankton are in it. The factors that register the signs of zooplankton development in the caught lakes are revealed: the frequency of flooding, water temperature, the content of consumption for a number of taxa — the gas regime. Studies have shown that that the zooplankton of the caught reservoirs is subject to increased impact of the communities of the special territory of rivers and lakes of the above-floodplain terrace of the distribution of faunal diversity, increased species richness and specific species structure.

The species diversity and spatial distribution of ichthyoplankton in the shelf and deep-sea waters of the northern half of the Black Sea near the Crimean Peninsula and the shores of the Caucasus under the conditions of prolongation of the summer hydrological season 2020 for September–October are presented. The high temperatures of the upper layer of the sea, peculiar of the summer spawning season, caused a continuation of productive spawning of warm-water fish. Eggs and larvae of 19 species from 12 families were identified in the ichthyoplankton. The maximum number of eggs was 302 ind./m², and larvae — 58 ind./m². Eggs and larvae of the mass commercial species Engraulis encrasicolus (L., 1758) dominated, whose share in the total population was 92.9 and 84.2% respectively. The highest abundance of ichthyoplankton corresponded to areas with minimal dynamic activity and maximum warming within the limits of coastal-shelf quasi-stationary anticyclonic vortices characteristic of the summer hydrological season.