| Summary: | Human activity since the Industrial Revolution has increased global greenhouse gas concentrations resulting in rapid climate change, which now threatens terrestrial and marine ecosystems. Tropical coral reefs, along with the biodiversity and communities they support, are particularly threatened by these changes in climate. Corals are a consortium of organisms, with the coral host along with its photosynthetic endosymbiont (Family Symbiodiniaceae) and diverse community of microorganisms (bacteria, archaea, fungi, and viruses) together forming the ‘coral holobiont’. However, the symbiosis between tropical corals and Symbiodiniaceae algae is sensitive to even small changes in temperature and ‘coral bleaching’ events – the loss of symbiosis – are now occurring with increased frequency and severity. These bleaching events can result in coral mortality and loss of entire reefs if stressful conditions do not subside. While research efforts have increased our ability to understand and predict coral bleaching events, fundamental questions remain surrounding how genetic diversity of the coral holobiont and interactions with its environment can drive coral resilience or resistance under climate change. The overarching goal of my dissertation is to understand how various abiotic (i.e., stress duration, spatiotemporal variation on the reef) and biotic (i.e., holobiont diversity, symbiosis) factors determine a coral’s response to environmental change at the level of phenotype and genotype. To achieve this goal, I first tested how environmental history and stress duration modulated the physiological responses of two reef-building corals under combined ocean warming and ocean acidification conditions. I found that one species was more stress-resistant (Siderastrea siderea), but that both duration of stress exposure and environmental history (inshore vs. offshore reef origin) modulated coral physiology. Next, I investigated the importance of holobiont genetic identity and abiotic environment in driving phenotypic responses of S. ...
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