Linking Physiological Effects Of Environmental Stressors From Cellular To Whole-Organismal Levels In The Early-Life History Stages Of Crassostrea Virginica (Eastern Oyster)

The Eastern oyster, Crassostrea virginica (Gmelin, 1791), is an ecologically and economically important species that resides in dynamic coastal ecosystems along the East and Gulf coasts of the United States. The success of oyster populations depends on the recruitment of their early life stages, which are especially vulnerable to environmental stress due to high developmental energy demands. As climate change continues, it is necessary to anticipate how the early life stages of the Eastern oyster will respond to environmental stressors under ecologically relevant scenarios. Therefore, the goal of this dissertation was to understand how the early life stages of C. virginica are physiologically affected by multiple global climate change stressors from a holistic perspective by incorporating local environmental data, observations across three life stages (i.e., carryover effects), responses from two important types of Eastern oysters, and physiological metrics from the cellular to whole-organism levels. To achieve this goal, chapter two observes the relative importance of three environmental tolerance mechanisms (selective mortality, carryover effects, and phenotypic plasticity) in shaping the performance of juvenile oysters in response to salinity exposures during the larval stage. Findings from this chapter indicate that typical differences in salinity among successive larval cultures in shellfish hatcheries likely do not impact performance as juveniles; rather, phenotypic plasticity likely underpins juvenile oyster performance as their physiology correlated with environmental conditions during the juvenile phase, not the larval exposures. Chapter three investigates carryover effects in more detail to explore how multiple global climate change stressors, ocean acidification and ocean warming, might affect the physiology of larval C. virginica, if those effects carry over to impact the performance of juvenile oysters and lastly, if those carryover effects change under different future environmental scenarios. Conditions of ocean acidification and ocean warming did affect the larval stage of the Eastern oyster and carry over into the juvenile stage, though these effects were nuanced and context dependent. Specifically, carryover effects from conditions of acidification were more persistent and negative, whereas warming had more fleeting carryover, and cross-tolerant, effects that were generally positive. Continuing to observe the effects of ocean acidification and ocean warming on the Eastern oyster, chapter four compares the larval responses of wild and selectively bred oysters. C. virginica larvae from wild and selectively bred oysters responded differently to conditions of acidification, but not warming. Furthermore, wild oyster larvae may be more resilient in the face of ongoing climate change. Despite exhibiting more lethal and negative effects of acidified conditions early in the larval stage, wild oyster larvae compensated for these earlier negative effects, while larvae from selectively bred oysters began showing signs of stress towards the end of the experiment. Lastly, exploring the development of carryover effects, chapter five observes how conditions of acidification during the settlement stage (i.e., settlement and metamorphosis) carried over to impact the juvenile stage. No detectable carryover effects were found, even though conditions of acidification negatively affected tissue growth at the beginning of the settlement stage. Overall, while Eastern oysters are able to withstand environmental stress to some degree, there were sub-lethal and carryover effects from multiple global climate change stressors identified in this dissertation that could have consequences for both wild and selectively bred populations in the future. The results from this dissertation will support subsequent studies to accurately predict the future success of wild oyster populations (e.g., effects to recruitment) and aquaculture production based on their physiological performances in the face of ongoing climate change