Assessment of swimming behavior of the Pacific oyster D-larvae (Crassostrea gigas) following exposure to model pollutants.

This study describes an image analysis method that has been used to analyze the swimming behavior of native oyster D-larvae (Crassostrea gigas) from the Arcachon Bay (SW, France). In a second time, this study evaluated the impact of copper and S-metolachlor pollutants on D-larvae swimming activity and the possible relationship between developmental malformations and abnormal swimming behavior. Analyses in wild and cultivated oyster D-larvae were investigated during two breeding-seasons (2014 and 2015) at different sampling sites and dates. In controlled conditions, the average speed of larvae was 144 µm s-1 and the maximum speed was 297 µm s-1 while the trajectory is mainly rectilinear. In the presence of environmental concentration of copper or S-metolachlor, no significant difference in maximum or average larval speed was observed compared to the control condition but the percentage of circular trajectory increased significantly while the rectilinear swimming larvae significantly declined. The current study demonstrates that rectilinear trajectories are positively correlated to normal larvae while larvae with shell anomalies are positively correlated to circular trajectories. This abnormal behavior could affect the survival and spread of larvae, and consequently, the recruitment and colonization of new habitats.

Can pesticides, copper and seasonal water temperature explain the seagrass Zostera noltei decline in the Arcachon bay?

Dwarf eelgrasses (Zostera noltei) populations have decreased since 2005 in Arcachon Bay (southwest France). Various stressors have been pointed out, however the role of xenobiotics like pesticides or copper (Cu) and of parameters like water temperature warming have not yet been explored. To determine their impact, Z. noltei individuals were collected in a pollution-free site and transferred to the laboratory in seawater microcosms. This dwarf eelgrass was exposed to a pesticide cocktail and copper, alone or simultaneously, at temperatures (10°C, 20°C, 28°C) representative of different seasons. After a two-week contamination, leaf growth, leaf bioaccumulation of Cu, and differential expression of target genes were studied. Eelgrasses bioaccumulated Cu regardless of the temperature, with reduced efficiency in the presence of the Cu and pesticide cocktail at the two higher temperatures. High temperature also exacerbated the effect of contaminants, leading to growth inhibition and differential gene expression. Mitochondrial activity was strongly impacted and higher mortality rates occurred. Experimental results have been confirmed during field survey. This is the first report on the impacts on Z. noltei of pesticides and Cu associate to temperature.

Combined effects of temperature and copper and S-metolachlor on embryo-larval development of the Pacific oyster, Crassostrea gigas.

This study evaluates the combined effects of two contaminants (copper and a herbicide S-metolachlor) and temperature on the early life stages of the Pacific oyster Crasssotrea gigas, which is native to Arcachon Bay (southwest France). The responses of D-larvae, obtained from wild and cultivated oysters, were investigated for one year during the oyster breeding period at different sampling sites and compared with the response of D-larvae from a commercial hatchery. Embryotoxicity was measured by considering the percentage of abnormal D-shaped larvae. Normal development of embryos occurred only from 22°C to 26°C. There were synergistic effects of copper at low and high temperatures. Native oysters appear particularly sensitive to an increase in water temperature, suggesting a future increase in the percentage of larval abnormalities as a result of global climate change. Hatchery oysters represent a good alternative model for studying the effects of both pollutants and climate change stressors.

Combined effects of pollutants and salinity on embryo-larval development of the Pacific oyster, Crassostrea gigas.

For several years, low larval recruitment has been observed in Arcachon Bay, in southwest France. Exposure to pollutants could partly account for the reduction of early life stages of the Pacific oyster. This study evaluated the effects of copper and S-metolachlor in combination with salinity on the early life stages of Crassostrea gigas. Embryos were exposed to concentrations of copper (1, 10 and 50 µg L(-1)) or S-metolachlor (10, 100 and 1000 ng L(-1)) and six salinities (18, 21, 24, 27, 30 and 33 u.s.i). Embryotoxicity was measured by considering both the percentage of abnormalities and arrested development in D-shaped larvae. Embryo-larval development was only affected at salinities ≤24 u.s.i, which have never been observed during C. gigas reproduction period in Arcachon Bay. Both contaminants had an effect at environmental concentrations. Our results suggest that copper and metolachlor toxicity was enhanced with decreasing salinity.