INDIVIDUAL AND POPULATION-LEVEL CONSEQUENCES OF AN ALGAL EPIBIONT ON DAPHNIA

In spring 1990 an algal epibiont (Synedra cyclopum var. incisa) infested cladocerans and copepods in Lake Mendota, Wisconsin. Daphnia pulicaria and Daphnia galeata mendotae were particularly infested (mean maximum diatom density, 22,900 cells animal-1). Laboratory experiments revealed that infested Daphnia had greater sinking and filtering rates than uninfested animals. Respiration rates were not significantly different between the two groups. Field-collected animals were counted and scored for degree of infestation, number of eggs, and total body size. Abundance of both adult and immature Daphnia increased only after the epibiont no longer infested Daphnia. Clutch size was not significantly different between infested and uninfested Daphnia, but death rates were higher during the period of infestation. This increased mortality is attributed to added stress on individuals caused by the epibiont, demonstrating the translation of physiological effects into population level consequences.