Ecotoxicological investigation of cyanobacterial crude extracts to Daphniamagna under subchronic test conditions

Abstract

Cyanobacterial blooms often consist of mixtures of microcystin-producing and microcystin-free species and both of them can cause unpredictable effects on aquatic organisms. In this work, the subchronic effects of the cyanobacterial crude extracts (CCEs) from microcystin-producing and microcystin-free cyanobacteria, with different microcystin concentrations (1, 10, and 50 µg L −1) on Daphnia magna (D. magna) were investigated. The life-history trait responses of D. magna to CCEs were determined based on survival, reproduction, and somatic growth. In addition, the physiological response represented by the feeding rate of D. magna on green algae (Scenedesmus sp.) after exposure to both type of crude extracts was also estimated. Our results showed that both microcystin-containing (MCCE) and microcystin-free (NCCE) crude extracts insignificantly reduced survival but strongly enhanced reproduction and somatic growth of organisms. However, the degradation of eggs and neonates of the gravid females exposed to the CCEs was observed. Besides, the feeding rate of D. magna exposed to MCCE has been increased significantly whereas no change in the feeding rate was observed for NCCE-exposed D. magna. In general, new and interesting aspects of the toxicity of MCCE and NCCE were obtained from this study and our study contributed to the understanding of the toxicity of Pseudanabaena sp. extract on D. magna under bioassays.