Changes in species composition of the cladoceran community in the highly eutrophic Lake Kasumigaura were investigated over 14 years (1976 - 1989). The composition was stable in summer, when small-sized cladoceran species, especially Bosmina fatalis, became dominant. Fish predation, high water temperature and the inhibitory effect of blue-green algae on cladoceran feeding seemed to induce this. In addition, a stable food supply for Cladocera by blue-green algae through the detritus food-chain may be partly responsible for the stability in species composition during summer. In contrast, the species composition in spring, fall and winter (non-blooming seasons for blue-green algae) changed from year to year. Daphnia ambigua and D. galeata often established large populations in these seasons after 1984; they appear to reduce greatly the algal biomass by their grazing.Article信州大学理学部付属諏訪臨湖実験所報告 7: 105-112(1991)departmental bulletin pape
