The impact of the toxic strain of Microcystis aeruginosa on Daphnia magna

The effects of the toxic strain of Microcystis aeruginosa on mature female Daphnia magna were studied under controlled laboratory conditions. Daphnids cloned from a single female were grown at 1 mg C l(-1) of Chlorella vulgaris until they reached the second adult instar. After production of a second clutch of eggs, some females were subjected to 1 mg C l(-1) of M. aeruginosa for two subsequent instars; remaining animals served as a control at 1 mg C l(-1) of C. vulgaris. D. magna had significantly decreased survivorship, dry body weight, and production of neonates when fed only toxic cyanobacterium. Animals lost weight, ceased reproduction and died on the sixth day of the experiment. Neonates born to mothers previously exposed for 5 days to M. aeruginosa, were smaller and lighter than newborns produced under the Chlorella treatment. Although increased mortality of D. magna fed Microcystis suggests toxicity effects, responses in growth and reproduction were similar to starvation. Possible consequences of cyanobacteria to neonate fitness are discussed.