Award: OCE-1737207

This project focused on understanding how Crassostrea virginica oysters from different regions in the Gulf of Mexico will be affected by ongoing and predicted changes to salinity and temperature caused by a warming climate and altered rainfall patterns. Although C. virginica is adapted to estuarine conditions and can tolerate broad ranges of salinity and temperature, there are limits to how long oysters can survive at environmental extremes, especially when multiple stressors occur concurrently. Local adaptation to salinity was tested by measuring survival in progeny of C. virginica from four populations in Louisiana and Texas spanning a broad range of salinity conditions. Upper critical thermal limits were measured for these progenies, as well as how those limits were affected by extreme salinity. Salinity tolerance varied among C. virginica stocks acclimated to extreme salinities in the laboratory. The highest salinity Texas stock performed worse at lower salinities and better at higher salinities than the lower salinity Louisiana stocks. The moderate salinity Texas stock performed as well as the high salinity Texas stock at high salinity and as well as the low salinity Louisiana stocks at low salinity. Field results supported these laboratory findings, indicating local adaptation of C. virginica to salinity. Mortalities differed between the two acute salinity tolerance trials, likely due to differences in the size of oysters and magnitude of salinity change between trials. The response of C. virginica following acclimation to low salinity in the laboratory was the only good predictor of low salinity tolerance in the field. When exposed to increasing temperatures, C. virginica thermotolerance was influenced by salinity, with the combination of extreme temperature and salinity having greater effects on mortality than either individual stressor. Oysters from all Texas and Louisiana stocks were most sensitive to increasing temperatures at low salinity, with mortalities occurring more quickly than at moderate and high salinities. At moderate salinity, mortality for all C. virginica stocks occurred most slowly, with high cumulative mortalities at the highest temperatures. Results indicate that the response of C. virginica to changing future salinities, for example from altered frequency, duration, and magnitude of rainfall events, will be modified by concomitant predicted increases in temperature. By identifying populations of C. virginica that are the most resilient to environmental changes, results may be used to inform and guide future resource management, ecological restoration, and/or oyster farming efforts. Study findings are incorporated into courses at Texas A&M University-Corpus Christi, a federally designated Hispanic Serving Institution. The study supported the training of 1 PhD student, 2 MS students, and 1 undergraduate student in ecological field sampling, planning, designing, and carrying out manipulative laboratory experiments, data analysis, and scientific writing. Two of the students were women, and one was from a traditionally underrepresented minority group. Last Modified: 01/25/2022 Submitted by: Jennifer Pollack