TRACKING THE PARENTAL CONTRIBUTION OF THE EASTERN OYSTER Crassostrea virginica THROUGHOUT HATCHERY PRODUCTION USING MICROSATELLITE MARKERS  

A century of overfishing, habitat destruction, and disease introduction have left stocks of the Eastern oyster, Crassostrea virginica, at historically low levels in Chesapeake Bay, prompting wide-ranging restoration efforts to restore the fishery and the ecosystem services that oysters provide. A major component of the current restoration strategy involves the hatchery production and planting (enhancement) of millions of juvenile oysters to increase abundance and enhance recruitment at neighboring tributaries. However, as with any large-scale restoration program, concerns exist over the maintenance of diversity and effective size (N_e). Diversity and N_e can be maintained by minimizing the variance in reproductive success among parents of out-planted oysters, however, specific features of oyster life history, practical husbandry constraints and cost may hinder such efforts. High and variable early life-history mortality among hatchery-produced oysters has the potential to dramatically reduce genetic diversity, but currently, no genetic monitoring of restored oysters exists in Chesapeake Bay. The present study was conducted as a first step to examine diversity and the variance in reproductive contribution among parents during multiple phases of hatchery production of oysters for restoration in Chesapeake Bay

Following typical protocols for the production of spat for restoration at the Horn Point Oyster Hatchery, we performed group spawns in three cohorts made up of ~20-30 parents and took larval samples for genotyping at d9 and d14 and a post-settlement sample (spat). Five microsatellite markers were used to assess diversity and to assign offspring to the parents at each time point. The number of effective breeders (N_b) will be estimated at each time point using several different methods.

Preliminary results for a single marker genotyped in 22 parents and 100 spat (one cohort) show that the number of alleles and allelic richness are significantly reduced in the offspring (A = 22 vs 11.711). The spat sample showed higher observed heterozygosity but lower expected heterozygosity - neither comparison was significant. The exclusion probability across 5 markers was 99.9% and the genotyping error rate very low (0.01), which will facilitate detailed parentage analys