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ENVIRONMENTAL AND BIOLOGICAL EFFECTS ON NUTRITIONAL MODE AND RESOURCE PARTITIONING IN SCLERACTINIAN CORALS
|Title:||ENVIRONMENTAL AND BIOLOGICAL EFFECTS ON NUTRITIONAL MODE AND RESOURCE PARTITIONING IN SCLERACTINIAN CORALS|
|Authors:||Wall, Christopher Bennett|
|Contributors:||Donahue, Megan (advisor)|
Marine Biology (department)
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|Publisher:||University of Hawai'i at Manoa|
|Abstract:||Reef corals are threatened by climate change. Increasing atmospheric CO2 has resulted in ocean acidification (OA) and ocean warming, which contribute to reductions in coral growth and to widespread coral bleaching events. The resilience of coral reef ecosystems to climate change fundamentally relies on the physiological resilience of reef corals to environmental change. Coral resilience may be supported by (i) biomass reserves, (ii) the capacity to switch feeding modes from autotrophy to heterotrophy, and (iii) the flexibility to associate with stress tolerant endosymbionts (Family: Symbiodiniaceae). To better understand the physiological response of corals to natural and human-induced environmental stress, I used a combination of laboratory and field studies to examine the tradeoffs in these three aspects of coral physiological resilience under ocean acidification stress, bleaching and post-bleaching recovery, and light limitation.|
First, under ecologically relevant irradiances, the coral Pocillopora acuta does not exhibit OA-driven reductions in calcification as reported for other corals. Instead, reductions in biomass reserves suggest that OA induced an energetic deficit and contributed to the catabolism of tissue biomass. Second, coral bleaching had extensive effects on the biomass of Montipora capitata and Porites compressa, and isotope mass balance revealed that changes in coral δ13C values were best explained by changes in tissues (proteins:lipids:carbohydrates) not a greater reliance on heterotrophy during bleaching or recovery. Finally, M. capitata-Symbiodiniaceae holobionts exhibited distinct traits and δ13C isotope values that differed between seasons and were modulated by light-availability. δ13C isotopic values did not reveal changes in nutritional modes, but instead suggest lower rates of carbon fixation/translocation by the symbiont Durusdinium, in agreement with laboratory studies identifying Durusdinium as an opportunist symbiont providing less nutritional benefit to the host. Together, my research provides insights into the complex consequences of environmental change on reef-building corals. Moreover, physiological tradeoffs that underlie coral resilience may mask the full effects of climate stressors on coral reefs. My work highlights the need for future research to consider (i) energetic costs and growth tradeoffs, (ii) biomass compound-specific isotope values, (iii) and the role of seasonality and (iv) symbiont community effects.
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Ph.D. - Marine Biology|
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