Changes in autumn zooplankton in the pelagic zone of Lake Sevan (Armenia) during the increase in fish abundance

The qualitative composition and structure of the autumn zooplankton in the pelagic zone of Lake Sevan in years that were characterized by different abundancies of fish are described. In October 2013, upon the increase in whitefish abundance, the species richness of zooplankton increased insignificantly; the values of the trophic coefficient and the Shannon index, calculated by the number, increased; and the specific number of Rotifera and Cladocera decreased. At the same time, atypical changes were recorded in the development parameters of zooplankton invertebrates. They were expressed as an increase in the total biomass due to Cladocera, among which large Daphnia (Ctenodaphnia) magna Straus occupied the leading position. The possible reasons for the particular changes in zooplankton are discussed.