Acute salinity and thermal challenge on genetic subpopulations of eastern oyster, Crassostrea virginica, in the western Gulf of Mexico

Aquaculture of Crassostrea virginica is expanding in the Gulf of Mexico, a region where low-salinity, warm-temperature conditions are common and associated with substantial oyster mortality. Reduced mortality rates may be possible with oysters selectively bred to survive during suboptimal salinities and high temperatures. Major sources of genetic variation in salinity tolerance may exist within the two distinct genetic subpopulations of C. virginica in the western Gulf of Mexico: the northern Gulf subpopulation and southern Texas subpopulation. To examine the salinity tolerance of oysters from each subpopulation in high temperatures, first-generation oysters derived from wild oysters collected in either northern or southern Texas were challenged at 34°C at either a low (2), control (30), or high (50) salinity condition. The target of 75 % mortality was reached in nine days at low salinity and twenty-one days at high salinity. Oysters derived from northern Texas died faster than those from southern Texas in both the low and high salinity challenge. Cox proportional hazards models revealed region of origin (northern vs. southern) was statistically significant in both challenges. The risk of mortality was 3.1 times greater (95 % CI: 1.99 – 4.73) for northern oysters at low salinity. A significant interaction existed between region of origin and grow-out site at high salinity. Higher survival of southern oysters supports previous findings and suggests the population may be particularly tolerant of extreme salinity at elevated temperatures. Field tests are needed to evaluate the effectiveness of salinity-thermal challenges for selecting for improved survival in the field. • More than 75 % of oysters died within 10 days at salinity 2 and 34°C. • Northern died faster than southern Texas subpopulation at low and high salinity. • Grow-out site had a significant impact on survival at high salinity.