Understanding Zooplankton Communities in Farm Dams: the Importance of Predation

Abstract

The species composition, species abundance and size distribution of the zooplankton community of four farm dams in the Adelaide Hills were largely controlled by predation. In three farm dams without fish, winter-spring zooplankton communities were dominated by the large cladoceran Daphnia carinata and a species of the large calanoid Boeckella along with smaller populations of Calamoecia, Ceriodaphnia, Mesocyclops leuckarti and Asplanchna brightwelli. The mean length of zooplankters in each of the dams was 0·95, 1·28 and 1·33 mm, and the largest zooplankters were 3·6 mm. In summer, large populations of the notonectid Anisops deanei decimated the zooplankton and virtually eliminated D. carinata. Mean length of zooplankters in each dam was 0·60, 0·81 and 0·83 mm, and no specimens were more than 1·60 mm. In the dam heavily stocked with redfm (Perca fluviatilis), the zooplankton community was dominated by Tropocyclops sp., Mesocyclops leuckarti, Bosmina meridionalis, Ceriodaphnia spp., Brachionus spp. and Asplanchna spp. D. carinata and calanoids were absent. Mean and maximum sizes of zooplankters were 0·50 and 0·83 mm in winter and 0·37 and 0·80 mm in summer. The roles of dispersal, competition and predation in determining community structure are discussed. Consideration is given to how the type and extent of predation and the environmental conditions might affect the importance of predation in other farm dam or pond systems.