Effects of differing concentrations of microcystin-producing Microcystis aeruginosa on growth, reproduction, survivorship and offspring of Daphnia magna

Abstract

The effects of differing concentrations of a microcystin-producing strain of Microcystis aeruginosa on the life history characteristics of adult Daphnia magna were studied in long-term experiments under controlled laboratory conditions. D. magna clones from a single female were grown at 2 mg C l -1 of Chlorella vulgaris. After producing the fifth clutch of eggs, D. magna were subjected to different concentrations of M. aeruginosa (0, 3, 6, 12, 25, 50, and 100%) in mixed suspensions with C. vulgaris at combined food concentrations of 2 mg C l -1 . After 6 days of exposure there was a decrease in survivorship, body weight, production of eggs and number of viable neonates with increasing Microcystis concentration. Neonate weights were significantly lower from mothers that had been exposed to pure Microcystis, compared to mothers fed pure Chlorella. The overall pattern showed an increase in neonate weight at low Microcystis concentrations (0-0.24 mg C l -1 ), but decreases at higher concentrations. At Microcystis concentrations above 0.5 mg C l -1 mortality, growth and reproduction were similar to the effects of starvation. Adult Daphnia recovery rate from exposure to toxic Microcystis was related to the exposure concentration of Microcystis. The effects were reversible at low concentrations of Microcystis, (0.06-0.5 mg C l -1 ), but above 0.5 mg C l -1 Microcystis animals did not recover and died. Continuous and linear losses in the body weight of Daphnia with concentration of Microcystis suggest the starvation-like effects on D. magna are caused by either cyanotoxin that is ingested or a chemical produced by Microcystis that inhibits feeding.