Cooperative Fish and Wildlife Research Units Program: Louisiana
Education, Research and Technical Assistance for Managing Our Natural Resources

High-frequency recording of valve opening behavior (VOB) in bivalves has been widely used to detect changes in environmental conditions. Generally, though, focus is put on a single variable such as temperature, salinity, the presence of a toxicant, or harmful algae in the surrounding water. Description of routine VOB under non-stressful conditions is also important to interpret responses to changes in surrounding conditions. Here we present the first detailed quantitative investigation of the in-situ VOB response of eastern oysters to environmental variables and their rates of change under conditions typically considered not stressful. The VOB of 8 eastern oysters (Crassostrea virginica) was monitored continuously for 7 weeks in a Louisiana estuary. We examined the relationship between VOB metrics (inter-individual variability, the probability of an oyster being closed, and the rate at which oysters closed their valves), and abiotic variables (temperature, salinity, and chlorophyll-a (chl-a) concentration), the rate of change in those abiotic variables, and the rate of change in water depth. The relationship between oyster VOB responses and environmental variables was analyzed through statistical models including no rate of change variables, the change from the previous measurement, and rates of change over 1-, 6-, 12-, and 24-hour time steps. All responses were best explained by the 12-hour time step model. The interaction between salinity and the rate of change of salinity had the most impact on inter-individual variability. Salinity had the most impact on the rate of valve closure, with oysters closing faster at higher salinities; chl-a had the most impact on the probability of oyster being closed, with oysters more likely be closed at lower chl-a concentrations. Significant interactions were found between many environmental variables, indicating the high level of complexity of oyster behavior in the natural environment. These interactions provided some insight into potential links between the VOB and the energetic physiology of oysters. For example, we showed that even with low salinities (< 5), oysters can remain open when enough food (chl-a) is available to support the costs of osmoregulation. VOB thus appears as a determinant factor in the capacity of oysters to maintain and conserve their metabolic and physiological functions in response to ever-changing conditions. This study contributes to the better understanding of the impact of environmental parameters variations on oyster behavior and could help inform predictive tools for restoration initiatives and fisheries practices.