UC San Diego

Anthropogenic climate change is forecasted to increase in both severity and frequency, making it important now more than ever to be able to understand how coral will fare in the changing environment. Yet a prevalent gap in knowledge on coral physiology prevents accurate determination of coral health and energetics on the reef. The goal of my thesis was to investigate coral energy metabolism in two Caribbean coral species, Porites astreoides and Orbicella franksi. To this end, I analyzed coral samples that had been collected during expedition to the Smithsonian Tropical Research Institute (STRI; Bocas del Toro, Panama) in 2015 and 2016. One set of coral samples had been collected from 3 m and 8 m depth from the Punta Caracol reef and exposed to comparable light intensities in STRI’s experimental aquarium for 10 days. A second set of samples had been collected from Punta Caracol and Eric’s Reef at ~6.0 m depth after a one-year reciprocal transplant experiment. Punta Caracol is nestled inside the turbid Bahia del Almirante lagoon – with large influxes of terrestrial runoff – whereas Eric’s Reef is facing the open ocean – experiencing higher seawater mixing. At Scripps Institution of Oceanography, I measured the enzymatic activity of malate dehydrogenase (MDH), citrate synthase (CS), lactate dehydrogenase (LDH), strombine dehydrogenase (SDH), and alanopine dehydrogenase (ADH) as proxies for maximum aerobic and fermentative metabolic capacity in coral. My results suggest differences in the metabolic regimes between coral collected from different depths, generally favoring higher fermentative activity in coral from 8 m. Short-term exposure to alternative light intensities did not induce significant effects to enzyme activity, suggesting the lack of an adaptive response, or that such was not needed. Corals from the transplant experiments demonstrated differences in fermentative pathway preferences whereby enzyme activity was primarily dependent on the destination reef; however, the responses were species-specific and, in many cases, opposite each other. These diverse responses after long-term acclimation to reefs with different environmental characteristics exemplifies the importance of characterizing coral energy metabolic regulation as it pertains to better assessing coral vulnerability and resilience in a changing environment.