Department of Geography, University of British Columbia, Vancouver, BC, Canada.
Institute for the Oceans and Fisheries, University of British Columbia, Vancouver, BC, Canada.
Glob Chang Biol. 2021 Aug;27(15):3474-3486. doi: 10.1111/gcb.15676. Epub 2021 May 24.
Climate change and warming ocean temperatures are a threat to coral reef ecosystems. Since the 1980s, there has been an increase in mass coral bleaching and associated coral mortality due to more frequent and severe thermal stress. Although most research has focused on the role of temperature, coral bleaching is a product of the interacting effects of temperature and other environmental variables such as solar radiation. High light exacerbates the effects of thermal stress on corals, whereas reductions in light can reduce sensitivity to thermal stress. Here, we use an updated global dataset of coral bleaching observations (n = 35,769) from 1985 to 2017 and satellite-derived datasets of SST and clouds to examine for the first time at a global scale the influence of cloudiness on the likelihood of bleaching from thermal stress. We find that among coral reefs exposed to severe bleaching-level heat stress (Degree Heating Weeks >8°Cˑweek), bleaching severity is inversely correlated with the interaction of heat stress and cloud fraction anomalies (p < 0.05), such that higher cloudiness implies reduced bleaching response. A Random Forest model analysis employing different set of environmental variables shows that a model employing Degree Heating Weeks and the 30-day cloud fraction anomaly most accurately predicts bleaching severity (Accuracy = 0.834; Cohen's Kappa = 0.769). Based on these results and global warm-season cloudiness patterns, we develop a 'cloudy refugia' index which identifies the central equatorial Pacific and French Polynesia as regions where cloudiness is most likely to protect corals from bleaching. Our findings suggest that incorporating cloudiness into prediction models can help delineate bleaching responses and identify reefs which may be more resilient to climate change.
气候变化和海洋水温升高对珊瑚礁生态系统构成威胁。自 20 世纪 80 年代以来，由于更频繁和更严重的热应力，大规模珊瑚白化和相关珊瑚死亡的情况有所增加。尽管大多数研究都集中在温度的作用上，但珊瑚白化是温度和其他环境变量（如太阳辐射）相互作用的结果。强光会加剧热应力对珊瑚的影响，而光照减少则会降低珊瑚对热应力的敏感性。在这里，我们使用了一个更新的全球珊瑚白化观测数据集（1985 年至 2017 年，n=35769）和卫星衍生的 SST 和云数据集，首次在全球范围内研究了云量对热应力导致白化的可能性的影响。我们发现，在暴露于严重白化级热应激（度加热周>8°Cˑweek）的珊瑚礁中，白化严重程度与热应激和云量异常的相互作用呈负相关（p<0.05），即云量越高，白化反应越低。采用不同环境变量集的随机森林模型分析表明，采用度加热周和 30 天云量异常的模型最准确地预测了白化严重程度（准确度=0.834；科恩氏 Kappa=0.769）。基于这些结果和全球暖季云量模式，我们开发了一个“多云避难所”指数，该指数确定了赤道太平洋中部和法属波利尼西亚是云最有可能保护珊瑚免受白化的区域。我们的研究结果表明，将云量纳入预测模型可以帮助描绘白化反应，并确定可能对气候变化更具弹性的珊瑚礁。
