Comparative field study of Crassostrea gigas (Thunberg, 1793) and Crassostrea virginica (Gmelin, 1791) in relation to salinity in Virginia

To evaluate and compare the performance of triploid juvenile C. gigas (mean shell height = 19.2 mm) and triploid juvenile Crassostrea virginica (mean shell height = 31.7 mm), 600 oysters of each species were deployed for 1 year in floating mesh cages at three replicate sites within low, medium, and high salinity regimes (respectively, 25ppt) in the Chesapeake Bay and the Atlantic Coast of Virginia. The comparative performance of the two oyster species varied with salinity. At low salinity sites, cumulative mortality of C. virginica (10%) was significantly (P < .05) lower than that of C. gigas (63%), and over-all mean growth rate of C. virginica (2.9 mm mo super(-1)) was significantly (P < .05) higher than that of C. gigas (1.6 mm mo super(- 1)). At medium salinity sites, survival and growth rate of C. virginica and C. gigas were not significantly (P > .05) different. Both species experienced moderately high cumulative mortality at the medium salinity sites - 35% for C. virginica and 53% for C. gigas - but considerable variation among sites was observed. At high salinity sites, mean cumulative mortality was similarly low (