Spatial heterogeneity of communities of unicellular plankton in the coastal arewas of the Kama reservoirs cascade

The peculiarities of development of planktonic communities of unicellular pro- and eukaryotes (phytoplankton, bacterioplankton and ciliates) in the coastal zones of Kama hydroelectric power reservoir cascade in two different hydrological periods were studied. 577 species of phytoplankton and 190 species of ciliates are identified in the reservoirs and their tributaries. Variability of abundance and biomass of the investigated groups of organisms at individual stations is very large, so the differences between the reservoirs are statistically unreliable. Their spatial distribution is generally consistent with the model of “spot dynamics”. Nevertheless, significant changes in the ratios of dominant taxa of phytoplankton and ciliate community composition of different reservoirs and at different hydrological periods are revealed. During the summer low water period, undulating pattern of species diversity and discrete changes of the phytoplankton and ciliates communities structure developed along the long axis of the cascade. This pattern is not evident in the period of spring flood. Our data show that the concept of “river continuum” proposed for unregulated rivers is not applicable to the Kama cascade reservoir system.