Effets chroniques de Microcystis aeruginosa et Oscillatoria sp., prélevées de la retenue El Kansera (Maroc), sur la survie et la reproduction de Daphnia magna Strauss

Abstract The aim of this study is to investigate the effects of two cyanobacteria (Microcystis aeruginosa and Oscillatoria sp.) on the survival and reproduction of Daphnia magna (Cladocera). Juvenil animals were exposed individualy in 100 ml vessels to different food (Scenedesmus) and cyanobacteria (Microcystis ou Oscillatoria) concentrations at 20°C and a 16: 8 L/D cycle. There were 10 replicates per treatment combination. The time of exposure was 21 days, a period sufficient for estimation of the population intrinsic growth rate. The animals were transferred to fresh treatment media each two days. M. aeruginosa and Oscillatoria sp reduced survival and reproduction of D. magna. The toxic effect increased with increasing concentrations of cyanobacteria and decreasing concentrations of Scenedesmus crassus. Juveniles were more sensitive than adults to high levels of M. aeruginosa. Furthermore, the study results show that aged cultures of cyanobacteria were more toxic than fresh one.