USING PLEISTOCENE FOSSIL ASSEMBLAGES TO ESTABLISH A BASELINE FOR CHESAPEAKE BAY OYSTER RESTORATION

The eastern oyster, Crassostrea virginica, is declining in abundance throughout the Chesapeake Bay due to sediment influx, disease, pollution, and overharvesting. Although ecological and historical records are limited to the past 400 years, the Pleistocene record in the mid-Atlantic stretches back almost one million years and may provide a baseline for ecological restoration. Pleistocene data can be leveraged to understand how shell height, biological age, growth rates, and population density varied before human disturbance.

The goal of this study was to reconstruct the size distribution, oyster growth rates, and population densities of Pleistocene oyster deposits in Virginia, Maryland, and North Carolina, to facilitate comparison with colonial and historical data. Bulk samples were collected from six localities, which ranged in age from early to late Pleistocene and yielded 21 to 2400 oysters per locality. Shell height was measured for 2800 left valves and population density was quantified at the only intact field locality. Age was estimated using two techniques: (1) counting bumps on the medial surface of the hinge and (2) counting growth lines on bisected hinges. Modern and colonial data were compiled from the oyster management literature.

Late Pleistocene oysters are significantly larger than colonial or modern oysters, with substantially lower growth rates than the latter. Population density for Pleistocene reefs is an order of magnitude larger than modern estimates. Aging techniques yield statistically significantly correlated age estimates, but additional sclerochronology is required to ground-truth these data. This study suggests that, although current restoration efforts primarily focus on the raising and seeding of oyster larva, priorities need to shift to protecting large, disease-resistant oysters.