Factors Controlling Diurnal Distribution and Migation of Zooplankton in the Littoral Zone of Freshwater Lakes

Species diversity of zooplankton in the littoral zone of lakes is higher than pelagic zone due to presence of the genus Chydoridae и Macrotricidae. The most of cladoceran species which are considered as pelagic are typical in the littoral zone. Higher diversity is determined by heterogeneity of littoral habitats. Fish and invertebrate predator pressure are the main factor influencing on diurnal distribution and migration of zooplankton. In the different lakes phytoplankton abundance may increase as in a direction to the pelagic of water-body and wise versa. The influence of macrophyte metabolites on development of the different phytoplankton species may be both negative and positive. Metabolite concentrations in the natural condition are sufficient to effect directly on zooplankton and other animals. Experiments show that cladocerans avoid macrophyte beds in the absence other signals. In the temperate zone zooplankton migrate in the daytime toward macrophyte beds in the presence of fish kairomones and wise versa in subtropical lakes. Daphnia avoids macrophytes even in the presence of predator cues. Its may be explained by the higher abundance of planktivorous fish and invertebrate predators especially in macrophyte beds of subtropical lakes. macrophyte beds are a good refuge for zooplankton which may control phytoplankton bloom in temperate lakes even under nutrient enrichment. In the low latitudes only submerged vegetation give a weak refuge for zooplankton under strong pressure of predators which have high density in the all habitats. Fish graze preferably of largebody species and small zooplankton cannot provide clear-water control. Furthermore, the differences in fish pressure leads mainly to horizontal zooplankton migrations in the temperate lakes and vertical migrations in the subtropical shallow lakes. Cardinal distinctions in functioning water communities in lakes of different climatic zones may be a basis for the prognosis of possible consequences of global warming.