Intracellular basis of climate change resilience in oysters

Climate change is making the world's oceans warmer and more acidic. This environmental disturbance represents a major threat to marine life, particularly to calcifying organisms, such as oysters. Although adaptation to climate change is possible for many marine species, the intracellular basis of such stress-induced modifications is largely unknown. This thesis aims to discover the biological mechanisms that provide heritable protection against the adverse effects of climate change stressors in oysters. I explore the molecular processes underlying the improved performance of selectively bred populations of Sydney rock oysters (Saccostrea glomerata) under acidifying conditions. The thesis assesses the intracellular responses of CO₂-resilient and wild type (non-selected) oysters following single or transgenerational exposures to elevated CO₂ using transcriptomics, proteomics and cytology. The molecular profiles of CO₂-resilient oysters were also investigated in response to a combination of CO₂ and thermal stresses. It was found that elevated CO₂ affected different levels of biological complexity,ranging from changes in cellular structures (mitochondria and associated systems) to alterations in protein concentrations and gene expression. The data showed that oysters are highly responsive to ocean acidification, and that discrete populations of oysters differ in their responsiveness. CO₂-resilient oysters exhibited differential regulation of genes and proteins involved in a variety of fundamental cellular processes, including control of the cell cycle, maintenance of cellular homeostasis, energy metabolism and stress responses. Transgenerational exposures to elevated CO₂ further altered the transcriptional profiles of oyster populations, suggesting that they may also be able to undergo rapid acclimation or adaptation to CO₂ at the transcriptional level. However, concurrent exposure to CO₂ and thermal stresses did not produce additive or synergistic effects on the molecular responses of CO₂-resilient oysters. This indicates that the inherent capacity of selectively bred oysters to better cope with CO₂ stress may not extend to ocean warming, or that the addition of thermal stress overwhelms oyster stress responses. Overall, the thesis reveals the molecular processes that may enable marine organisms to survive and thrive as climate change progresses. I conclude by considering the implications of this knowledge to ecosystem dynamics and fisheries production, highlighting potential strategies to minimise the impacts of this imminent threat.