Environmental emergent problems: the influence of the reproduction cycle in a freshwater sentinel species submitted to climatic and chemical stressors?
Résumé
Currently, the study of the fate and adverse effects of toxicants remains increasingly complicated in a global change context. Although no consensus was established between the occurrence of extreme events and global changes, the frequency and the magnitude of heat waves is still increasing. The basal metabolic activity of sessile aquatic organisms could be strongly affected, limiting thus their defence capacity facing to additional stresses. This study aimed to assess the combined effects of a multi-metallic stress and recurrent heat waves in a freshwater bivalve, Dreissena polymorpha, during contrasted reproduction cycle steps. Mussels were exposed to an environmental concentration of a nickel-chromium mix solution (20 μg.L-1 and 5 μg.L-1, respectively) for 40 days. A gradual increase of the temperature (+15°C) was weekly performed in exposed media for 24 hours. The same experimental design has been set up in the reproduction (May-June) and the rest (November-December) periods. Key metabolism functions were targeted along the biological organisation levels through a panel of markers. Different physiological patterns of responses were highlighted between both sexes and reproduction cycle stages. An effect of recurrent heat waves was observed in females while males’ one was only impacted by the multi-metallic stress. Mussels exposed to the combined stress showed a decrease of the global metabolic activity compared to organisms exposed to the simple stress conditions. This study pointed out the need to include global change issues and temporal variations for further ecotoxicological investigations. This study questioned about classical used approaches in ecotoxicology, which often do not consider confounding factors.