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

Abstract

This study describes an image analysis method that has been used to analyze early life stages behavior of native oysters (Crassostrea gigas) from the Arcachon Bay (SW, France). In a second time, this study evaluated the impact of Cu and S-metolachlor pollutants on D-larvae behavior and 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 control condition, 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 aberrant behavior could impacts the survival and spread of larvae and consequently the recruitment and colonization of new habitats.

Molecular and phenotypic effects of early exposure to an environmentally relevant pesticide mixture in the Pacific oyster, Crassostrea gigas.

“…Similarly, Kuchovská et al [83] did not find reduction of the swimming speed of C. gigas larvae upon pesticide exposure. In contrast, early exposure to single pesticide compound, such as chlortoluron (from 0.015 µg.L -1 ), reduced the swimming speed of oyster Dlarvae along with growth and developmental issues [28], while other compounds like glyphosate, isoproturon or S-metolachlor did not, even at relatively high concentrations compared to the one used in this study (11.1 µg.L -1 , 7.8 µg.L -1 and 1µg.L -1 respectively) [28,87]. Interestingly, the effects of the herbicide chlortoluron, a pesticide used in our cocktail, occurred at ecologically relevant levels (0.015 µg.L -1 ) [28].…”

Pesticide mixture toxicity assessment through in situ and laboratory approaches using embryo-larval stages of the pacific oyster (Magallana gigas)

“…EC 30 of imidacloprid and propiconazole were calculated to be 70.50 and 1.26 mg/L, respectively (Kuchovská et al, 2021). The effect of the mixture thus seemed to be slightly attenuated but insufficiently to be classified as antagonism, which is defined by a minimum two-fold difference (Cedergreen, 2014) No effects were found on the swimming speed or the trajectory paths in this study even though SM (10 and 1000 ng/L) decreased the rectilinear trajectories in the study of Gamain et al (2020). The rectilinear trajectory is considered as the major one at this developmental stage of the oyster larva, unlike later stages, when helical swimming is the most useful for hunting prey, finding a settlement, or avoiding predators (Maciejewski et al, 2019).…”

“…This is an interesting finding which should be 1. explored further in the future to assess if it is a usual proportion of swimming paths of larvae exposed in situ and 2. compared with larvae of the same age exposed in the laboratory to find out if it is a baseline locomotive activity at that age, or 3. if it is a direct effect of the water quality. Gamain et al (2020) established a link between erratic larval behavior and the presence of developmental malformations. In this study, negative control containing about 17 % of abnormal larvae exhibited predominantly (around 80 %) rectilinear, normal, trajectories, whereas 100 ng/L of S-metolachlor induced around 44 % of abnormal larvae with mostly circular trajectories.…”