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UBC Theses and Dissertations

Integration of sea surface temperature and light for prediction of coral bleaching González Espinosa, Pedro Cuautémoc


Climate change represents one of the principal threats to coral reef ecosystems because of an increase in mass coral bleaching and associated coral mortality due to more frequent and severe thermal stress. Even though most research has focused on temperature, coral bleaching results from the interacting effects of temperature and other environmental variables such as solar radiation. Exposure of corals to high light exacerbates the impact of thermal stress on corals, whereas reductions in light can reduce sensitivity to thermal stress. This dissertation aims to integrate the effects of light and temperature to assess how corals have responded to periods of cold and warm water, and under various future climate change scenarios. The synergetic effect of light is evaluated through the development of different models and methods. First, performing a logistic regression model approach on cold-water bleaching observations I find that cold-water bleaching can be best predicted with an accumulated cold-temperature metric (Degree Cooling Weeks), although the effect of light marginally improved prediction accuracy. Second, using mixed-effects models on a global database of warm-water bleaching observations and environmental metrics, I find that coral reefs exposed to severe bleaching-level heat stress show a reduced bleaching response if exposed to high cloudiness. Then, I developed a ‘cloudy refugia’ index which identifies regions where cloudiness is most likely to protect corals from bleaching. The findings suggest that incorporating cloudiness into prediction models can help identify reefs that may be more resilient to climate change. Finally, using mixed-effects models on future climate projections from GFDL-ESM4, I find that though warming ocean water is the primary driver of future coral bleaching conditions, cloudiness might delay the onset of frequent bleaching by four decades in low emission scenarios. However, the protection of clouds in addition to corals' ability to adapt to climate conditions are likely to be outpaced in high-emission scenarios. This research provides an overarching assessment of the influence of thermal stress and light on mass coral bleaching patterns globally. Furthermore, it demonstrates the value of including more driving variables when examining the fate of coral reefs in different future greenhouse gas emissions scenarios.

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