The Effects of a Simulated Suspended Sediment Plume on Eastern Oyster (Crassostrea virginica) Survival, Growth, and Condition

Bottom sediments are resuspended into the water column during dredging operations. These resuspended sediments are an often cited concern used to justify restrictions applied to dredging schedules in many areas of the USA. One example of a temporal restriction, commonly referred to as an environmental window, involves dredging schedules in the James River, Virginia, because of potential impacts on the eastern oyster (Crassostrea virginica Gmelin). Yet, effects' data are lacking to understand the effects of suspended sediments to C. virginica. To address this data gap, we performed a laboratory study mimicking sediment resuspension during annual dredging operations in the James River. Field-collected oysters were exposed for 7 days under flow-through conditions to 0, 100, 250, and 500-mg/L total suspended solids (TSS) in a unique exposure system where oyster movements could be electronically monitored. Endpoints analyzed were survival, percent of time open, total number of shell movements, weight change, and condition index. Data indicated no significant effects of suspended sediment on these endpoints after 7 days of exposure. Weight change in oysters attached vertically to monitor their movements was significantly less than in oysters not monitored in every treatment. No significant differences in condition index, an indicator of oyster growth sensitive to environmental pollutants, were observed among treatments measured 30 days postexposure. Correlations performed for each treatment among monitored oyster endpoints found significant negative associations between number of movements and percent open in the 100, 250, and 500-mg/L TSS treatments and in all treatments combined. These data will help reduce the uncertainty surrounding the effects of suspended sediments on C. virginica.