Southeastern Section - 62nd Annual Meeting (20-21 March 2013)

Paper No. 14
Presentation Time: 8:00 AM-5:30 PM


KUSNERIK, Kristopher M.1, GRANT, Amanda N.2 and LOCKWOOD, Rowan2, (1)Department of Geology, University of Georgia, 210 Field Street, Athens, GA 30602-2501, (2)Department of Geology, The College of William and Mary, P.O. Box 8795, Williamsburg, VA 23187,

Population levels of eastern oysters (Crassostrea virginica) in the Chesapeake Bay have declined precipitously during the past two centuries, due to disease, sediment influx, and overharvesting. To restore these populations, it is essential to establish baseline data on healthy reefs. This study focuses on a well-preserved late Pleistocene oyster deposit on the Piankatank River, Virginia. The population ecology of the reef, including age distribution, growth rates, and population density, provides a strong depiction of a thriving oyster reef. Additionally, studies of temperature, salinity, and tidal currents provide data on how the paleoenvironment differed from modern bay environments.

The deposit is divided into a larger, eastern section (17 meters long with a maximum height of 2.47 meters) and a smaller, western section (8 meters long with a maximum height of 2.04 meters). Fifteen bulk samples were collected along horizontal and vertical transects. Ages of the oysters were determined through two methods: counting the number of growth lines in the cross-section of the oyster hinge and counting the number of bumps on the hinges (“bump counting”). Preliminary data suggest that Pleistocene oyster populations had much higher concentrations of spat and juvenile oysters (x̄=31.4mm) and much higher population densities (x̄=6,212 oysters/m2) than modern reefs (300-500 oyster/m2). Calculated growth rates for the Pleistocene oysters were slower (x̄= 20.26 mm/yr) than the growth rates of the modern (x̄=21.6 mm/yr), but the difference was not statistically significant.

Amino acid racemization was applied to multiple specimens of Crassostrea and Mercenaria, yielding estimates ranging from 80-120 ky for this deposit. We attempted to reconstruct paleotidal current direction by comparing the orientation measurements of articulated oysters preserved in the reef, but no major trends were revealed. Salinity tolerances of 21 non-oyster species suggest a higher salinity environment (15 to 32 ppt) than the modern Piankatank River (6 to 23 ppt). Clumped isotope thermometry of Mercenaria specimens support a warmer environment than the modern temperature range. These factors suggest a more estuarine environment for the Pleistocene Holland Point reef than its current position on the modern Piankatank River.