Exceptional Thermal Tolerance of Coral Reefs in American Samoa: a Review
As climate change poses an ever increasing threat to coral reefs globally, understanding why particular corals are resistant to bleaching is paramount to their continued survival. The coral reefs of Ofu Island, American Samoa, provide a living laboratory to examine mechanisms of coral adaptation to extreme thermal conditions and serve as an analog for a future environment impacted by climate change. Three backreef pools exhibit remarkably different temperature regimes, which consequently results in varying levels of coral thermal tolerance. In pool 300, temperatures can reach 35 °C and fluctuate up to 6 °C throughout the day. Pools 400 and 500 are less variable, with temperatures rarely exceeding 32 °C. Yet, the pools contain a highly diverse community of corals, including an abundance of thermally sensitive species. This review summarizes the results of nearly two decades of research into the mechanisms contributing to differential bleaching resistance among pools. Factors examined include the effects of intermittent water flow, previous exposure to subbleaching temperatures, Symbiodinium genotype, modifications of genetic expression within the polyp, and the associated bacterial microbiome. Corals within the highly variable pool 300 appear to be more adequately adapted to thermal extremes by retaining chlorophyll concentrations during frequent heat pulses, associating with thermally tolerant endosymbionts, upregulating gene expression associated with heat acclimatization, and potentially possessing an advantageous microbiome composition. Though encompassing a small geographic area, the findings from Ofu’s reefs have widespread implications for coral conservation as they serve to elucidate the impacts of these many confounding factors and their contributions to bleaching resistance.
KeywordsAmerican Samoa National Park of American Samoa Ofu Island Coral bleaching Thermal tolerance
The author would like to thank D. Barshis, B. Fuiava, I. Moffitt, and two anonymous reviewers for their constructive comments and review of this manuscript.
Compliance with Ethical Standards
Conflict of Interest
The author is currently an employee of American Conservation Experience who works as a marine technician at the National Park of American Samoa. All parties state that there is no conflict of interest.
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