A PALEONTOLOGICAL PERSPECTIVE ON THE CONSERVATION OF CHESAPEAKE BAY OYSTERS

The goal of conservation paleobiology is to use the fossil record to provide a long-term perspective on conservation priorities and restoration efforts. The eastern oyster (Crassostrea virginica) is a possible candidate for this approach, since Chesapeake Bay populations have experienced a massive decline in the past two centuries, and remediation is hampered by a lack of long-term monitoring data. During the past four years, my collaborators and I have explored whether the Pleistocene fossil record can provide information on oyster body size, growth rates, and population density. Although C. virginica are easily preserved, fossil assemblages are patchily distributed, environmentally variable, and rapidly disappearing due to erosion control practices. Thus far, we have sampled 11 Pleistocene sites (representing 3500 specimens), ranging from Delaware to South Carolina, from field or museum collections.

Assessment of population dynamics has been difficult, due to the problem of biologically aging specimens. Previous studies have relied on shell length, resilifer bumps, and banding in bisected hinges to estimate biological age. To evaluate the accuracy of these techniques, 200 modern oysters of known age were collected from four Chesapeake Bay sites. Sclerochronological data were also collected from four Pleistocene specimens. Although preliminary, these results suggest that banding in bisected hinges is more accurate and less prone to ecophenotypic variation than other techniques. In modern C. virginica, environment exerts a strong influence over shell size and shape, not to mention predation, encrustation, and boring. Each of the fossil localities was therefore assessed with respect to paleoenvironment based on substrate type and associated mollusks.

Even with paleoenvironmental control, late Pleistocene oysters are substantially larger, with lower growth rates than modern Chesapeake oysters. Both early and late Pleistocene oyster assemblages document higher population densities than modern oysters from the mid-Atlantic region. Possible implications for conservation include using sea level predictions to prioritize locations for reseeding; establishing a maximum shell length for harvest; and shifting focus from oyster spat release to the preservation of older disease-resistant adults.