Availability of suitable phytoplanktonic food for zooplankton in an ice-covered lake

Edible phytoplankters were found throughout the winter in a shallow ice-covered lake in Pennsylvania, U.S.A., in conjunction with a diverse population of zooplankton. Environmental conditions during the winter seemed to eliminate large and non-motile types of algae in favor of the smaller motile forms which may be the best foods for zooplankters. The phytoplankton were classified for study both by systematic position and by size group. The total volume of phytoplankton comprising the group Chrysophyta and algae 80 µ declined rapidly during the period of ice-cover, while algae 15 µ and Chlorophyta maintained more stable volumes. During the latter weeks of ice-cover phytoplankton densities were low (50–200/ml), and bacteria, detritus, or µ-algae (2 µ) not detected by the counting methods used, may have been important foods for the zooplankters. The lack of suitable phytoplanktonic foods may have contributed to the decline of calonoid copepods during the late winter.Based on a thesis submitted to the Department of Biology, East Stroudsburg State College, as a partial requirement for the degree of M.S. in Biology.