DEVELOPMENT OF THE ZEBRA MUSSEL, DREISSENA POLYMORPHA (PALL.), POPULATION IN A HEATED LAKES ECOSYSTEM. I. CHANGES IN POPULATION STRUCTURE

The zebra mussel, Dreissena polymorpha (Pall.), population in the Konin heated lakes system (Poland) during the 1993-2006 period was described. The zebra mussel population was studied at stations: Lake Lichenskie, Lake Slesinskie, discharge zone of post-cooling waters from the power plant, at four stations in the canals. The impact of the effective temperature sum on the development of the population varied widely in the different habitats of this ecosystem within the range of 3720 to 7600 degree days and vegetation time period of 188 to 345 days, depending on the populations proximity to the heated water discharge from the power plant. The population occurring in the warmest zone of the system was of a simple structure with few age classes, a lower maximum individual weight, and an unbalanced sex ratio. The occurrence of zebra mussels in these habitats was negatively correlated with water temperature. The abundance of D. polymorpha in the zone with moderate heating was positively correlated with the effective temperature sum