Changes in the Planktonic System of the Nuclear Power Plant Cooling Pond Related to the Invasion of Dreissenidae (Mollusca: Bivalvia)

The introduction of mussels of the family Dreissenidae into the cooling pond of one of the nuclear power plants (NPP) of Ukraine, the Khmelnitsky NPP (north-western region), has caused significant changes both in the contour and in the pelagic parts of the techno-ecosystem. The following three periods were considered: (1) before the introduction of Dreissena polymorpha, (2) during the peak of its population development and (3) after the introduction of a second species of Dreissena and declining of abundance of Dreissenidae. We recorded a decrease in taxonomic richness and abundance of phytoplankton with the increase of the effect of D. polymorpha. No such changes were registered for the zooplankton community. The relationship between the biomass of phytoplankton and zooplankton were quite complex. In addition, the relations of diversity indicators of the phyto- and zooplankton communities were different during the three study periods: negative in the first, positive in the second and none in the third period. We concluded that the invasion of Dreissenidae into the water bodies and its effect on the ecosystems should be considered not only from the standpoint of their direct influence on the water transparency and phytoplankton abundance; this invasion could affect all the components of the pelagic and contour subsystems.