Ecotoxicological investigation of cyanobacterial crude extracts to Daphnia magna under subchronic test conditions

Authors: TAN DUC NGUYEN, XUAN QUANG NGO, THANH LUU PHAM, THANH SON DAO

Abstract: Cyanobacterial blooms often consist of mixtures of microcystin-producing and microcystin-free species, and both 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 μgL$^{-1}$)on Daphnia 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 types of crude extracts was 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, degradation of eggs and neonates of the gravid females exposed to CCEs was observed. In addition, the feeding rate of D. magna exposed to MCCE 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 revealed by this study, which contributes to the understanding of the toxicity of Pseudanabaena sp. extract on D. magna under bioassays.

Keywords: Cyanobacteria, ecotoxicology, feeding rate, life-history traits, somatic growth

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