ABSTRACT
The ecology of Dreissena polymorpha (zebra mussel) was studied over the past 50 years (1959-2010) in lakes of northeastern Poland, especially lakes in the Masurian Lakeland. This species was very common, being found in 60%–100% of lakes studied during the rst 30 years of this period. Densities differed between and within lakes over time. Examination of environmental parameters in different lakes indicated densities were not strongly dependent on any single factor but could be related to trophic status. In general, densities were highest in large and deep lakes of mesotrophic and meso-eutrophic status. D. polymorpha was absent or occurred in low densities in shallow, hypereutrophic, and polymictic lakes. In some lakes, populations declined to low levels in the 1970s through the 1990s as a result of increased eutrophication. With recent changes in agricultural practices and construction of sewage treatment plants, some recovery is now being observed. In most Masurian lakes, comparative densities were determined primarily by mortality of planktonic veligers during settlement and in the postveliger stage.
