STUDY OF THE ABILITY OF DAPHNIA-CARINATA KING TO CONTROL PHYTOPLANKTON AND RESIST CYANOBACTERIAL TOXICITY - IMPLICATIONS FOR BIOMANIPULATION IN AUSTRALIA

The properties of Daphnia carinata King as a grazer for use in biomani pulation trials were investigated. Mesocosm experiments suggested that in water from a lake where D. carinata was scarce, phytoplankton was nutrient-limited and the manipulated biomass of zooplankton had no eff ect on total chlorophyll a, whereas in water from a lake where D. cari nata was dominant, nutrients were not limiting and total chlorophyll a was negatively correlated with the manipulated biomass of zooplankton . When offered lake phytoplankton in feeding trials, D. carinata consu med all items present, including colonies of cyanobacteria and long fi laments of diatoms. In large outdoor tanks with natural plankton, the biovolume of prokaryotic ultraplankton (possible predecessors of cyano bacterial blooms) was consistently reduced in the presence of D. carin ata. There was no evidence of an adverse effect of single-celled Micro cystis aeruginosa containing the peptide toxin microcystin-LR on D. ca rinata grazing rates or survival. Different concentrations of microcys tin-LR in solution covering the range of toxicities observed during M. aeruginosa blooms (5-500 nM) had no effect on D. carinata grazing. Th e suppression of phytoplankton biomass by D. carinata grazing is one o f several possible mechanisms that might be considered for biomanipula tion in Australia.