Seasonal studies on the zooplankton community of Lake Alexandrina, River Murray, South Australia, and the role of turbidity in determining zooplankton community structure

Abstract

Zooplankton was quantitatively collected from Lake Alexandrina from November 1975 until March 1978. Twenty-eight species of zooplankton were identified, although momentary species composition usually comprised two calanoids, one cyclopoid, from three to six cladocerans and from zero to four rotifers. There were no consistent patterns in the vertical or horizontal distribution of the major zooplankters. Some species, including Boeckella triarticulata, Calarnoecia ampulla, Bosrnina meridionalis, Ceriodaphnia quadrangula and possibly Daphnia carinata were perennial, whereas Diaphanosorna unguiculaturn, Moina rnicrura and Daphnia lumholtzi were seasonal. Zooplankton density was relatively high and constant throughout the study. The zooplankton community included both large and small species. In Lake Alexandrina, high turbidity may preclude size-selective fish predation, allowing the persistence of large species, while invertebrate predation may be insufficient to remove small species.