Qualitative changes in the planktonic Cladocera assemblage of a High Tatra Mountains lake during the last 100 years

During the last roughly 100 years (1881–1989) some noteworthy changes have occurred in the planktonic Cladocera taxocene of the lake Popradske pleso (High Tatra Mts., Czecho-Slovakia). Primarily, in course of the twenties up to the fifties of our century Daphnia pulicaria and Polyphemus pediculus, and later also Holopedium gibberum, disappeared from the plankton of the lake. Conversely, approximately from the mid-seventies, Daphnia longispina has become a constituent of the lake plankton. In spite of lacking data on the principal parameters of the abiotic and biotic environment from the past, the author assumes that probably the most important factor responsible for the changes referred to were fluctuations in the predation pressure of fish. Besides, organic pollution might have played a definite but less important role.