ACCURACY AND REPEATABILITY OF BIOLOGICAL AGING METHODS FOR CRASSOSTREA VIRGINICA (EASTERN OYSTER): APPLICABILITY TO FOSSIL AND ARCHAEOLOGICAL SPECIMENS

Crassostrea virginicaare extremely important, both ecologically and economically, in North American estuarine environments. They filter the water and provide hard substrate for other organisms. When oyster populations were at their peak, they provided millions of dollars in annual revenue to local communities in the Chesapeake Bay region. Several methods for determining the biological age of fossil and modern oysters have been developed and applied over the last century; however, verifying them for accuracy or repeatability has proven difficult. The ability to biologically age oysters will make it possible to reconstruct population dynamics from archaeological middens and the fossil record. These demographics will help us understand how oyster communities were structured in the past and the extent to which restoration is possible.

The three methods commonly used to biologically age oysters include: (1) bump counts, which involves counting the number of bumps on the shell hinge; (2) growth lines, which involves counting the number of lines visible on the cross section of a shell hinge; and (3) shell height, which involves measuring the maximum dorsal-ventral dimensions of the shell. We applied these three methods to approximately 175 Crassostrea virginicashells aged 1-6 years, (approximately 25 shells per age class) sampled from the York River (Virginia). Multiple users counted growth lines and bumps to identify the extent to which they were repeatable from user to user. We used a Kolmogorov-Smirnov test to determine normality, and then applied Pearson Product Moment and Spearman rank tests to correlate the three metrics.

Both the number of bumps counted and the number of growth lines were statistically significantly correlated with biological age (R₁₈₂=0.758, p < 0.001; R₁₆₀=0.891, p < 0.001). These results indicate that growth line counting is the most accurate metric for biologically aging oysters. This also suggests that paleontologists, archaeologists, and ecological managers would benefit from standardizing their techniques to facilitate the comparisons of data across multiple disciplines. For future work, we will be expanding this study to include approximately 80 additional oysters, 1-4 years of age, sampled from the Potomac River (Virginia).