GROWTH RATES AND SCLEROCHRONOLOGY OF MODERN CRASSOSTREA VIRGINICA FROM THE LOWER CHESAPEAKE BAY (SOUTHEASTERN VIRGINIA)

Populations of the Eastern Oyster (Crassostrea virginica) have declined over the last century in the Chesapeake Bay due to anthropogenic factors including climate change and overharvesting. Oyster lifespan is a useful proxy for overall reef health but is difficult to assess without time-consuming and expensive methods, such as sclerochronology. Although morphological proxies for lifespan (such as growth-band counting) have been identified in Pleistocene C. virginica, it is unclear whether these same approaches can be applied to modern specimens. This study has three main objectives: (1) quantify maximum lifespan and growth rates in a small sample of modern C. virginica from the Chesapeake Bay, (2) compare growth rates of modern C. virginica to Pleistocene specimens from similar environmental conditions, and (3) assess the validity of growth-band counting as a proxy for estimating lifespan in modern oysters, which would help reduce the cost and time required for certain sclerochronological analyses.

Over 1,400 oysters were sampled in 2020 and 2021 from Baines Creek and Felgates Creek, which are tributaries of the Elizabeth and York Rivers, respectively, in southeastern Virginia. The oysters were sampled from a restored, intertidal reef at Baines Creek and a restored, subtidal reef at Felgates Creek, both of which are currently protected from harvesting. The largest ten live oysters from each reef were cleaned, their left valves were bisected at the hinge, and the hinges were embedded in epoxy. The longest three hinges for each of the two sites were processed for sclerochronology. Sample line density varied from 7 to 8 tracks per cm of the hinge, making it possible to collect multiple samples of shell powder per year of original shell growth. A total number of samples collected per hinge varied from 80 to 120. Oxygen and carbon isotope analyses were performed to quantify the number of years each oyster lived and the extent to which growth banding in the hinge corresponds to annual cycles. Preliminary results indicate that, at least for the intertidal site, growth banding in the hinge may provide an accurate estimate of lifespan. Lifespan was shorter and growth rates were significantly faster for the six modern shells compared to Pleistocene localities, despite similar temperature and salinity growing conditions.