SCHLEROCHRONOLOGY AND STABLE ISOTOPE VALUES OF CRASSOSTREA VIRGINICA COLLECTED FROM LATE EIGHTEENTH CENTURY MIDDENS AT STRATFORD HALL, VIRGINIA

The Colonial Plantation of Stratford Hall on the Northern Neck of Virginia, owned by Revolutionary War hero Henry Lee (1756 - 1818), and birthplace of Robert E. Lee, included a number of slave quarters that generated middens. Six oysters collected from the Stratford Hall middens were analyzed for growth histories and stable isotope values. Scanning Electron Microscopic (SEM) imaging of the growth bands along an axial transect across the internal umbo divulged a quadripartite seasonal record of growth to include interpreted intervals that corresponds to winter (January-March), spring (April-June), late summer (July-September), and fall (October-January). A computer-controlled robotic micromill was employed to isolate discrete aliquots of calcite powder for isotopic analysis at the University of Saskatchewan.

The six specimens of Crassostrea virginica ranged in age from 5-8 years with an average of age of 6.5 years. Growth rates averaging ~14.2 mm per year generally declined throughout the life history of the oysters. In the context of seasonal variability, maximum growth rates occurred during late summer (July-September) with a minor exception for two of the specimens. δ¹⁸O values display a reasonable correspondence to variability with changes in growth patterns. Values ranged from -7.4 to -0.9 δ¹⁸O‰ VPDB with an average of -5.1 δ¹⁸O‰ VPDB. The greatest variability typically occurs between the fall and spring interval.

Growth rates decrease and δ¹³C values generally increase by ~1% through ontogeny oxygen as metabolism slows. Variations in δ¹³C and δ¹⁸O record annual and/or seasonal shifts in temperature and/or salinity in response to climatic variability at the height of the Little Ice Age II.