Performance of selectively-bred lines of eastern oyster, Crassostrea virginica, across eastern US estuaries

Eastern oyster, Crassostrea virginica, aquaculture has expanded greatly in recent years, but further growth of the industry is constrained by disease-related losses. Oyster breeding programs supporting the oyster aquaculture industry along the east coast of the US have targeted resistance to three prominent diseases: MSX, Dermo, and ROD, caused by Haplosporidium nelsoni, Perkinsus marinus, and Roseovarius crassostreae respectively. Consequently, selected oyster lines possess some level of resistance and/or tolerance but the extent to which these lines, derived from various programs, perform across diverse growing environments used by industry has not been tested. The performance of six selected eastern oyster lines was evaluated at five sites along the east coast of the US (Maine to Virginia) to 1) identify differences in performance among lines at each site, and 2) identify lines that perform well across all sites. Performance measures included growth, mortality, and yield over a 15-month evaluation period. During unusually high mortality events, subsets of oysters were processed for disease diagnosis. Growth trajectories were similar among lines within a site, but varied significantly across sites (78% of random variance explained). Oysters grown in Rhode Island were largest while oysters grown in Maine were smallest at the end of the study. Mortality varied greatly among lines at each site as well as among sites. Line × site interaction explained 61% of the total random variance in the mortality data. In Maine, extensive mortality was observed early in the year for all lines, coincident with increased ROD prevalence. In New Jersey and Virginia, unusually high mortality was evident in the UMFS, Clinton, and NEH-RI lines during the final months of the experiment when the prevalence of both Dermo and MSX were 100% and <. 50%, respectively. NEH, DEBY, and hANA lines were less affected, demonstrating that lines selected to perform better in their native site surpassed those selected outside the area. Despite large and significant line × site interaction effects for mortality and yield, NEH, DEBY, and hANA performance was above average across all sites. These findings have important implications for oyster breeding strategies and industry practices.