Abstract
The projected increase in frequency and intensity of hypoxia is expected to have negative impacts on Scleractinian corals. The effects of increased temperature and lowered pH are well documented for corals; however, the threat of hypoxia has received less attention. While hypoxia alone may not be an immediate threat to the persistence of coral reefs, the compounded impact of multiple climate change stressors represents a significant challenge to coral resilience and survival. Before the complex interaction of multiple stressors can be unraveled, it is critical to comprehensively elucidate the impacts of hypoxia in isolation and at multiple intensities. This dissertation aimed to uncover the physiological and metabolic response of multiple scleractinian coral species, including Acropora cervicornis, Siderastrea radians, Siderastrea siderea, Porites astreoides, Porites porites, and Orbicella faveolata, to diverse hypoxia conditions encompassing (1) acute, severe deoxygenation, (2) long term diel hypoxia, (3) long term diel hypoxia under ocean warming, and (4) chronic, stable hypoxia. A combination of laboratory techniques including intermittent flow respirometry, buoyant weight and vertical extension measurements, and tissue sample biopsies were used to identify significant metabolic suppression, changes in growth rate, and the utilization of multiple anaerobic pathways under the aforementioned hypoxia regimes. This dissertation demonstrates the high variability of acute hypoxia tolerances among different coral species, elucidates the species-specific responses under sustained hypoxia, confirms the additive negative effects of thermal stress and hypoxia, and reveals the differential utilization of anaerobic pathways among different coral species. The results presented here highlight the ineffectiveness of a universal hypoxia threshold and demonstrate the importance of considering ocean deoxygenation when predicting the resilience and community structure of coral reefs under climate change.