Environment-forming influence of Castor fiber L. on zooplankton communities of small rivers in the territory of the M. G. Sinitsyn Kologrivsky Forest State Nature Reserve

The zooplankton of small rivers in the territory of the M. G. Sinitsyn Kologrivsky Forest State Nature Reserve (Kostroma region) was studied under the influence of a zoogenic factor. 107 species were identified among zooplankton. Of these, 42 species belong to Cladocera, 19 species - to Copepoda, and 46 species - to Rotifera. The dominant species were identified and the values of abundance, zooplankton biomass, Shannon species diversity index and Piel uniformity index were determined for small rivers Seha, Ponga, Lomenga, Londushka, Chornaya, Talitsa in areas exposed to zoogenic activity and in areas not affected by Castor fiber L. The environment-forming role of the beaver for zooplankton communities, the influence of Castor fiber activity on the species composition, quantitative indicators of zooplankton, and a complex of abiotic factors (temperature, pH, BOD5 values, and specific electrical conductivity) were noted. Using statistical methods, it was revealed that in the conditions of zoogenic activity, the abundance, biomass of zooplankton, and the species diversity index are significantly higher, but Piel uniformity index is lower compared to areas not exposed to zoogenic transformation. Zoogenic activity influences abiotic factors, thereby indirectly affecting zooplankton communities. Under the influence of the zoogenic factor, the temperature of the water body, the values of the hydrogen index, and the values of biological oxygen demand (BOD5) are higher, but the specific electrical conductivity is lower. In the small rivers of the studied area of the southern taiga, the common beaver is a habitat-forming species for zooplankton. This animal slows down the flow of watercourses, contributes to an increase in water temperature, influences other abiotic environmental factors, and forms specific refugiums for zooplankton communities.