Plankton in pelagic zone of lake Sevan (Armenia) in case of low density of fish and an increase in water level

Raising water level and decreasing regulation through the fish promoted occurrence and massive development in two species of cladocerans in plankton - Diaphаnosoma brachyurum Lievin и Daphnia (Ctenodaphnia) magna Straus of high mountain Lake Sevan, and their maximum quantity and biomass were registered in 2012. Increase in the water transparency, reduction in the quantity and the biomass of phyto- and bacterioplankton, increase in the proportion of blue-green algae in the planktonic algae composition, increase in the total biomass of zooplankton, decrease in the diversity and biomass of rotifers was also observed. All of these changes may have been conditioned by the influence of the bioactivity of Cladoceras.