Peculiarities of zooplankton cenosis structure and development in the middle water area of Kremenchuk Reservoir, Dnieper River (Ukraine), in conditions of elevated temperatures
An analysis of the research results on the quantitative and qualitative composition of zooplankton in the middle part of the Kremenchuk reservoir in the water area near Chervona Sloboda, Lesky, and Khudyaki in August 2016 is presented аt elevated temperatures. Of particular note is the first decade of the month, when there was a shift in maximum temperature to +25.42 ± 0.15°C (Cv=1.86%). In general, the water temperature was unstable; its maximum values were a stress factor for plankton invertebrates of the reservoir. It is established that for each section of the water area, certain specific Rotifera species are characteristic of zooplankton: Hexarthra mira (Hudson, 1871)–at station 1; Lepadella patella (O.F. Muller, 1786), Mytilina mucronata (Müller, 1773), Brachionus forficula Wierzejski, 1891, Br. budapestinensis (Daday, 1885)–at station 2; Polyarthra euryptera (Carlin 1943; Bartos 1950; Nipkow 1952; Sudzuki 1964), Lecane luna (Müller, 1776), Synchaeta monopus (Plate, 1889), Asplanchna priodonta var. henrietta Langhans, 1906, Alona quadrangularis (O.F. Müller, 1776)–at station 3. The total zooplankton quantity and the temperature of the aquatic environment increased from the top to the bottom, and the difference between them was 3.3 times in number and 2.4 times in biomass. A positive close and significant correlation (k=0.83 and k=0.65, respectively) with changes in the temperature factor of the aquatic environment in space was established. This indicates the adaptation of aquatic organisms to the environmental conditions where they occupy habitats most favorable for their habitat. On average, the basis of zooplankton was formed by eurythermic organisms-rotifers 64 ± 1.23% in number and 33 ± 6.18% in biomass, which are better adapted to significant fluctuations in daily temperature (recorded differences of 2-8°C/day). Branched crustaceans, mostly thermophilic, accounted for only 7-41% in number and 8-19% in biomass, indicating unfavorable conditions for their development. The close negative correlation (k=-0.78 and k=-0.60) of Cladocera biomass with maximum temperatures indicates the death of primarily large forms of branched crustaceans under the influence of elevated temperatures. Thus, temperature changes, as the influence of climatic factors, has more negative than positive effects. The influence of extreme temperatures of weather conditions leads to a decrease in the productivity and feeding of this aquatic ecosystem.