Interannual Changes in the Quantitative Parameters and Structure of Invertebrates in the Littoral and Pelagic Zones of Lake Sevan (Armenia) with Fluctuations in Meteorological Conditions and Fish Biomass. I. Summer Zooplankton

Abstract

Based on an analysis of interannual changes in the summer zooplankton of the littoral and pelagic zones in Lake Sevan, the relationship between the quantitative characteristics of the communities with the level regime, the amount of precipitation, the average monthly temperature from April to July, and ichthyomass is shown. Fluctuations in the water level are positively correlated with the amount of precipitation. The effect of dilution is detected upon an increasing water level, which indirectly indicates that the amount of accumulated nutrients in the lake exceeds that entering from the catchment area. The increase in the average monthly air temperature from April to July and the increase in the biomass of Prussian carp against the background of the decreasing biomass of whitefishes positively affect most zooplankton parameters. The richest zooplankton community is formed under conditions of low biomass of whitefish, maximum air temperature, and minimum rise in water level. However, the control from planktophages is the leading factor determining the zooplankton state in Lake Sevan. This is evidenced by a significant reduction in quantitative characteristics of plankton invertebrates due to crustaceans with an increase in the biomass of whitefish and a decrease in the biomass of Prussian carp in years with different temperature and level regimes.