The influence of a predatory ostracod,Australocypris insularis,on zooplankton abundace and species composition in a saline lake

The influence of the predatory ostracod Australocypris insularis on zooplankton abundances and species composition in an Australian saline lake was monitored over 8 months in aquaria and tank microcosms. Control, Predator (double A. insularis Control densities) and No Predator (all A. insularis removed) treatments were set up in small 11.5l aquaria and large 883.5l tanks. Microcosm salinities were manipulated to accord with seasonal lake salinities and ranged from 35 to 110 gl^-1. Densities of the calanoid copepods Calamoecia clitetellata and C. salina, the small ostracods Diacypris compacta and D. dietzi, and juvenile ostracods (excluding A. insularis) were significantly reduced by A. insularis predation in the aquaria experiments. Daphniopsis sp. was only present (in low numbers) in the No Predator aquaria. Results from the large tank experiments were not as clear-cut, due to difficulties in the manipulation of predator numbers. Differing salinity tolerances of predator and prey may confound the predation impact of A. insularis.