GLOBAL PROJECTIONS OF CORAL BLEACHING UNDER WARMING AND OCEAN ACIDIFICATION USING A MECHANISTIC MODELLING APPROACH
Global climate models project increased rates of mass coral bleaching such that many of the world's reefs will disappear by mid-century. Typically, models use a Degree Heating Week (DHW) – based bleaching threshold in combination with sea surface temperature (SST) output from global climate models. While these approaches are empirically justifiable, they are nonspecific in applying a generic bleaching threshold to all coral species and typically do not incorporate the potential for corals to adaptively respond to an increasingly warmer, more acidic ocean. We scaled up a mechanistic model of coral and symbiont ecological dynamics and symbiont evolutionary dynamics to the global scale, and estimate severe bleaching events based on declines in coral cover. The model was run for changes in SST and water chemistry predicted by the NOAA/GFDL Earth System Model 2 through 2100. We normalized the model to achieve a reasonable global severe bleaching frequency (~10%) between 1985-2010 based on ReefBase bleaching observations. Coral bleaching responses to rising SSTs are tested using susceptible versus tolerant coral types, with and without variation in symbiont thermal tolerance, and in combination with ocean acidification. Projected bleaching frequencies are also compared and contrasted regionally to results from previous DHW–based threshold models. A global mechanistic model provides a valuable tool for assessing the potential effects of genetic or community-level variation in symbiont thermal tolerance on projected rates of mass coral bleaching.
Logan, C. A., California State University, Monterey Bay, USA, email@example.com
Dunne, J. P., NOAA-GFDL, USA, firstname.lastname@example.org
Donner, S. D., University of British Columbia, Canada, email@example.com
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