Seasonal Dynamics of Zoplankton of the Sheksna Reservoir (Vologda Region)

Abstract

The paper analyzes the seasonal dynamics of the composition, structure, and abundance of zooplankton in different parts of the Sheksna Reservoir in 2016–2020. The zooplankton in the reservoir includes 107 species (Rotifera – 41, Cladocera – 41, Copepoda – 25). The authors have found 88 species in Lake Beloye and 90 species in the river part of the reservoir. 7 species in the lake and 17 in the river part of the reservoir have been found for the first time. The communities of different parts of the reservoir are similar in terms of zooplankton composition (76%). The highest level of dominance (0.32–0.38) of zooplankton is observed during the ice period. In Lake Beloye, this figure is higher than in the river part of the reservoir. A small set of species (Kellicottia longispina, Keratella cochlearis, Eudiaptomus gracilis) is characterized by high density in all seasons of the year. Some species are dominant only in certain periods. In summer, rotifers of the genus Polyarthra and Mesocyclops leuckarti dominate the entire water area of the reservoir. Lake Beloye is dominated by Daphnia galeata and Chydorus sphaericus in summer. The composition of the dominant zooplankton complex in different parts of the reservoir is similar in certain seasons. Only in May, the structure of the dominant complex of the lake and river sections of the reservoir differs. The ratio of dominants in Lake Beloye in May is similar to the ice period. The maximum abundance of zooplankton in the reservoir is recorded in summer. From May to November the largest number of copepods is observed. In March, rotifers dominate. Cladocera were noted as dominants only in the lake part of the reservoir. The seasonal dynamics of the structure and abundance of zooplankton generally corresponds to those in the 1970s and early 2000s.