Sclerochronological Basis for Growth Band Counting: A Reliable Technique for Life-span Determination of \u3cem\u3eCrassostrea virginica\u3c/em\u3e from the Mid-Atlantic United States

Widely used sclerochronological methods for biologically aging fossilized oysters, such as δ18O and Mg/Ca analyses, are costly, time-consuming, and not always practical for population-level analyses. A method that relies on visible morphological features, such as growth bands, to determine the lifespan of Crassostrea virginica would provide a cost-efficient and reliable alternative. Previous studies have assessed whether counting growth bands can be used to biologically age C. virginica from the southeastern U.S. but have produced conflicting results. For this study, we conducted subseasonal sclerochronological analyses on Pleistocene C. virginica from the mid-Atlantic U.S. to determine whether growth band counting could be used to reliably measure oyster lifespan. A highly significant correlation exists between δ18O peaks and major (annual) grey growth bands in these oysters. Major grey and white growth bands differ significantly with respect to δ18O values. These data suggest that, for C. virginica from the Pleistocene of the mid-Atlantic U.S., major grey growth bands are accreted during the colder months of the year and can be used as annual markers to biologically age specimens. The results presented here differ from previous studies that reported no link between growth bands and δ18O values, possibly because the latter focused on lower latitude regions with different seasonal temperature regimes and sampled only the early stages of growth, which contain morphological features that could be confused with major growth bands. While growth band counting of oysters shows promise as a method for biologically aging oysters that experience high seasonal temperature variability, future studies are needed to assess its applicability over a broader geographic range