Assessing the contribution of aquaculture and restoration to wild oyster populations in a Rhode Island coastal lagoon

The decline of the eastern oyster (Crassostrea virginica) has prompted various restoration and aquaculture efforts. Recent field surveys in Rhode Island suggest that wild populations are increasing, yet the factors contributing to expansion are unknown. We used a population genetic approach to characterize genetic differences between wild and cultured oyster populations and explore the extent of connectivity and admixture between groups. Individual oysters from four wild, three farmed, and two restored populations were collected within or just outside Ninigret Pond, a coastal lagoon highly influenced by human activity, and genotyped at 13 microsatellite loci. Results from the multi-locus genotype data showed that wild populations were more genetically diverse than the cultured populations. We also observed significant genetic differentiation between paired wild and cultured populations but not between pairs of wild populations. A cluster analysis detected substantial admixture between wild and cultured groups. As oyster aquaculture and restoration activities are forecasted to increase in the future, this study highlights the potential degree of genetic introgression between remnant wild populations and less diverse, hatchery-reared stocks. Those tasked with preserving our living natural resources should carefully consider how the juxtaposition of aquaculture, restored, and wild populations at small spatial scales will impact the genetic composition and evolutionary trajectories of species in decline for generations to come.