Appraisal of coral bleaching thresholds and thermal projections for the northern Red Sea refugia
Appraisal of coral bleaching thresholds and thermal projections for the northern Red Sea refugia
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DOI：
10.3389/fmars.2022.938454
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发表时间：
2022-11
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影响因子：
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通讯作者：
A. Eladawy;Takashi Nakamura;M. Shaltout;Asmaa H. Mohammed;K. Nadaoka;M. Fox;Eslam O. Osman
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文献类型：
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作者：
A. Eladawy;Takashi Nakamura;M. Shaltout;Asmaa H. Mohammed;K. Nadaoka;M. Fox;Eslam O. Osman
红海北部的珊瑚在不断增加的热应力下表现出很高的耐热性。据推测，整个红海的珊瑚具有相似的漂白阈值(32°C或更高)，因此红海北部地区珊瑚的漂白耐受性可能是由于环境水温较低(25-28°C)，远低于珊瑚的生理最高温度。红海对岸的漂白模式是否独立于当地最高月平均海水温度，并与假定的32摄氏度阈值保持一致，还有待确定。在这里，我们使用1982-2020年的遥感表层海温数据来模拟红海上与假设的珊瑚温度阈值30、31和32°C相关的度热周的空间分布。我们还使用耦合的模式比较项目阶段5的模型输出来预测不同温室气体代表浓度路径(RCP)下红海的变暖趋势。我们表明，应用32°C阈值显著减少了北部的有效度高温周，但不能减少红海中部或南部地区的有效热周，这一发现与整个红海历史上的漂白观测一致。此外，最极端的RCP8.5情景下的模型预测显示，到21世纪末(1998-2020年)，整个红海变暖约3摄氏度，与中部和南部地区(2.7-3.1摄氏度)相比，红海北部(2-2.5摄氏度)变暖不那么明显。这一升温速度将保持在红海北部假定的温度门槛以下，这将有助于该地区成为珊瑚未来几十年的避难所(即保持有利的温度)。总之，我们的结果支持这样的观点，即珊瑚在整个红海都有类似的阈值；因此，珊瑚漂白阈值与当地的最大月平均值无关。因此，如果区域变暖预测表明，红海北部在21世纪末之前不会达到假定的漂白阈值(32摄氏度)，北部地区的珊瑚礁可能是最后几个抵抗气候变化的珊瑚礁之一。
Corals in the northern Red Sea exhibit high thermal tolerance despite the increasing heat stress. It is assumed that corals throughout the Red Sea have similar bleaching thresholds (32°C or higher), and hence greater bleaching tolerance of corals in the northern Red Sea region is likely due to lower ambient water temperatures (25–28°C) that remain well below the corals’ physiological maxima. Whether bleaching patterns across the Red Sea are independent of the local maximum monthly mean of seawater temperature and aligned with an assumed 32°C threshold has yet to be determined. Here, we used remotely sensed surface sea temperature data spanning 1982–2020 to model spatial distributions of Degree Heat Weeks across the Red Sea in relation to assumed coral thermal threshold values of 30, 31, and 32°C. We also used the Coupled Model Intercomparison Project Phase 5 model outputs to predict warming trends in the Red Sea under different greenhouse gas representative concentration pathways (RCPs). We show that applying 32°C thresholds dramatically reduces effective Degree Heat Weeks in the north, but not in central or southern Red Sea regions, a finding that is consistent with historical bleaching observations throughout the Red Sea. Further, model predictions under the most extreme RCP8.5 scenario exhibited ~3°C warming by the end of the 21st century (1998-2020) throughout the Red Sea with less pronounced warming for the northern Red Sea (2–2.5°C) compared to the central and southern regions (2.7–3.1°C). This warming rate will remain below the assumed thermal threshold for the northern Red Sea which should help this region to serve as refugia (i.e., maintaining favorable temperatures) for corals to persist for decades ahead. Together, our results support the notion that corals have similar thresholds throughout the Red Sea; hence, coral bleaching thresholds are independent of the local maximum monthly mean. Consequently, where regional warming projections suggest the northern Red Sea will not reach assumed bleaching thresholds (32°C) before the end of the 21st century, coral reefs in the northern region may be among the last standing against climate change.