Date of Award

Summer 2019

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Holly D. Gaff

Committee Director

Richard C. Zimmerman

Committee Member

David Gauthier

Committee Member

Mark E. Warner


Scleractinian corals are animal partners in exquisite symbioses with a suite of algal, microbial, fungal and viral associates comprising miniature ecosystems collectively referred to as a holobiont. In recent decades, ocean warming has jeopardized the delicate balance of the very symbioses that have enabled coral survival. Thermal stress causes a reduction of algal symbionts, a phenomenon referred to as ‘coral bleaching’ that represents dysbiosis in the holobiont and often leads to mortality. Current thermal acclimation theory states variation and gradual increases in temperature can ameliorate thermal stress. Indeed, there is evidence some coral species have some capacity to acclimatize to thermally variable environments, increased temperature, or both, leading to enhanced thermal tolerance. However, disadvantages to thermal plasticity have been identified for several coral species, suggesting acclimation may not always be beneficial. In order to better understand coral thermal acclimation, this dissertation investigated the short-term acclimatization potential of two foundational reef species to natural thermal variability, compared thermal performance with acute and cumulative exposures in the absence of acclimation, and explored the potential of corals to acquire thermal tolerance. The studies presented here put the thermal stress response in a dose context to enable cross-experiment comparisons. Corals under gradual stress showed physiological plasticity on the part of the animal, but any benefits appeared to be limited by the algal partner. Acquired thermal tolerance may reduce bleaching in the short term, but whether acquired tolerance can increase recovery from bleaching requires investigation. Further, no signs of acclimatization to thermal microhabitat variability were detected in a seven-month period, and any small benefits of repeated thermal stress appeared to be short-lived. Hence, despite the adherence of coral respiration to the standing theory, there is overwhelming evidence that thermal acclimation, acclimatization and acquired thermal tolerance are insufficient to enable coral survival in the coming century. The majority of Scleractinian corals will not survive the pace of climate change, dictating the dire need for the restoration of the global carbon balance and other substantial human interventions.


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