Carbon Fixation of the Diverse Coral Symbiont Symbiodinium in a High-CO2 Ocean

EPA Grant Number: FP917197
Title: Carbon Fixation of the Diverse Coral Symbiont Symbiodinium in a High-CO2 Ocean
Investigators: Oakley, Clinton Alexander
Institution: University of Georgia
EPA Project Officer: Michaud, Jayne
Project Period: August 16, 2010 through August 15, 2013
Project Amount: $111,000
RFA: STAR Graduate Fellowships (2010) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Global Change


The focus of these studies is the reaction of the carbon fixation mechanisms of the coral/algal symbiosis to predicted future climate scenarios, particularly to what degree the Calvin cycle of Symbiodinium, the algal symbiont of corals, is impaired by elevated temperatures. How the large genetic diversity of Symbiodinium relates to variation in their physiological function will also be investigated, including Form II Rubisco CO2/O2 specificity and carbon compensation points. The amount of carbon supplied, or possibly limited, by the coral host under thermally stressful scenarios is also of interest.


Coral reefs are under threat from many stressors, including climate change and thermally induced coral bleaching. The algal symbionts of corals are genetically very diverse, but how this diversity relates to tolerance to future climate conditions of higher temperatures is unknown. This project will determine the thermal tolerances of diverse symbiont types and provide insight into their unique means of photosynthesis to better inform coral management and predict reef response to climate change.


A series of studies utilizing novel methodologies will identify key differential responses of photosynthesis of many types of Symbiodinium to environmental conditions consistent with predicted future climate scenarios. Measuring the absolute respiration and photosynthetic rates of O2 and CO2 production/fixation of Symbiodinium types in real time, both in culture and in coral fragments, across a range of temperatures will elucidate the contributions of the alga and the animal to carbon fixation. The CO2/O2 specificity of Form II Rubisco, unique among eukaryotes to Symbiodinium, will be determined in vivo under normal and thermally stressful conditions in multiple genetic types, as these parameters greatly influence the productivity of corals.

Expected Results:

Genetic diversity of Symbiodinium is likely to be reflected in differential physiological responses to environmental factors relevant to predicted future climate scenarios, but broad cladal identity is unlikely to determine physiological specialization. These physiological differences are expected to correlate with geographic location and habitat (depth, light regime, average summer maximum temperature) of the host(s). The Calvin cycle of Symbiodinium is expected to be susceptible to thermal impairment at temperatures that correlate to bleaching thresholds reported from the source organisms at the geographic point of collection, which can be used as a point of comparison. Form II Rubisco CO2 specificity will likely have a negative relationship with temperature. Carbon limitation of photosynthesis due to high temperatures may promote a positive feedback loop by increasing photodamage.

p>Potential to Further Environmental/Human Health Protection:

The proposed research will significantly contribute to our basic understanding of coral reef biology and bleaching susceptibility; provide greater knowledge of the Symbiodinium host and ecosystem specialization; and identify coral species most at risk of climate-driven decline to aid potential reef management strategies.

Supplemental Keywords:

coral reefs, coral, global climate change, algae, algal physiology, photosynthesis, CO2, Calvin cycle, ocean acidification, Rubisco, Symbiodinium,, RFA, Scientific Discipline, Air, climate change, Oceanography, Air Pollution Effects, Environmental Monitoring, Ecology and Ecosystems, Atmosphere, ecosystem models, extreme weather events, climate models, atmospheric oxidant concentrations, ecosystem sustainability

Progress and Final Reports:

  • 2011
  • 2012
  • Final