The Effect of Ocean Warming on the Coral Communities of Hawai‘i

Abstract

The Main Hawaiian Islands experienced unprecedented back-to-back coral bleaching events in 2014 and 2015. This event occurred in the context of the third and largest global bleaching event to date, which occurred from 2014-2017 and affected reefs in every tropical coral reef habitat around the globe. Bleaching disrupts the symbiosis between coral animals and their algal symbionts, and the physiological damage accrued during times of bleaching causes partial or full mortality and widespread events can have lastly impacts on the functional complexity and diversity of reef systems. In an attempt to better understand bleaching and its effects on reefs, my dissertation addressed the following questions: 1) What were the bleaching patterns at Lanikai in 2014 and 2015, and was there any evidence of acclimatization between years?; 2) Were there genomic differences between differentially bleached Montipora capitata next to each other on the reef?; 3) Are growth anomalies (GAs) of Porites evermanni morphologically and physiologically different?; and 4) How well did a citizen science reef monitoring project describe reef health and bleaching? Results revealed characteristic differences in species susceptibility and recovery of bleaching patterns at Lanikai and in situ degree heating weeks revealed Porites and Pocillopora colonies acclimatized to thermal stress from 2014 to 2015, bleaching less per unit area during significantly higher thermal stress. Analysis from genome scans of M. capitata found no strong underlying signals of selection to explain differential bleaching responses, despite all harboring clade C Symbiodinium. P. evermanni GAs showed characteristic morphological and physiological differences with larger corallites and less lipid energy reserves than normal tissue. While normally not reproductive, the GAs of P. evermanni were found to be extremely reproductive, illustrating there is still more to learn about these anomalous coral growths. And finally, the citizen science monitoring project provided an opportunity for the community to take part in understanding how climate change is affecting their reef. With the intensity and frequency of coral bleaching events predicted to increase, it is important now more than ever to understand the ecological, physiological, and molecular aspects of bleaching and the implications for the future of coral reefs.