Lethal and sublethal effects of sediment burial on the eastern oyster Crassostrea virginica

Eastern oysters Crassostrea virginica are dominant ecosystem engineers that construct complex reefs in estuarine systems. Reef persistence relies on reef growth, which must outpace reef degradation and sediment deposition. The quantitative impact of burial on oyster survival and sublethal effects of sediment deposition are undefined. In this mesocosm study, we quantified effects of partial and complete burial (0, 50, 70, 90, and 110% of oyster shell height) on survival, biodeposition, condition index and growth of oysters (shell height = 25-75 mm). Survival only declined significantly when 90% or more of an oyster was buried; the critical burial depth inducing 50% mortality was 108%. This finding will allow scaling of mortality rates of oysters as a function of sediment load and oyster size. Biodeposition and condition index were negatively related to burial depth, whereas shell growth increased with burial depth. Decreases in biodeposition and condition index were likely related to disruption of feeding by burial and reallocation of energy resources to shell growth. The increase in shell growth was analogous to vertical migration of infaunal species-buried oysters increased vertical shell growth to breach the sediment surface to feed and respire, at the expense of tissue growth. While oysters are tolerant of partial burial in terms of survival, burial adversely affects metabolic processes that influence demographic rates and reef persistence. Future management efforts should consider the effects of partial burial, which often occur more frequently than catastrophic burial events causing mass mortality.