Oyster Shells from Jamestown: Time capsules for the James River, VA

Oysters (Crassostrea virginica) and the reefs that they created were central to the ecology of the Chesapeake Bay prior to the early 20th century. When the colonists arrived in 1607, they would have had to navigate their way through massive three dimensional oyster reef communities in the James River that were exposed at low tide and created living "rocks" that posed serious hazards to their wooden ships on the way to Jamestown.

Studies of oyster populations, past and present, rely on various levels of information. At the most basic level, presence/absence data combined with measurements of oyster shells provides information on general population demographics and ecology. As oysters grow, they deposit internal signatures within their shells that are preserved through time much like the concentric growth rings made by trees. These internal shell signatures are used for oyster age and growth rate evaluation. Estimates of individual oyster ages and growth rates provides a means to describe population dynamics (age structure, recruitment patterns, mortality rates) as well as general trends in environmental conditions (water temperature, salinity) given the body of knowledge relating oyster growth to these parameters.

Our research on the Jamestown oyster shells addresses each of these information levels for the 1600 era shells using the same techniques that we are using to evaluate modern oyster shells collected from the James River during 2005-2008. The use of the same techniques for historic and modern collections will allow us to make comparisons within the James River habitat across time periods. 
A comparison by Harding et al. (2008) of historic (1611-1616 era) and modern (2005-2008) James River oysters collected at similar salinities indicates that historic oysters reach larger sizes than modern oysters at the same ages. 

This research has been made possible through a collaboration with the Association for the Preservation of Virginia Antiquities staff at Jamestown. 
Related publications 

Harding, J.M., Mann,R., and Southworth, M. 2008. Shell length-at-age relationships in James River, Virginia oysters (Crassostrea virginica) collected four centuries apart. Journal of Shellfish Research. 27(5). 1109-1115. 
Harding, J.M., Spero, H.J., Mann, R., Herbert, G.S., and Sliko, J.L. 2010. Reconstructing early 17th century estuarine drought conditions from Jamestown oysters. Proceedings of the National Academy of Sciences, USA. 107(23): 10549-10554.