Severe 2010 Cold-Water Event Caused Unprecedented Mortality to Corals of the Florida Reef Tract and Reversed Previous Survivorship Patterns

BackgroundCoral reefs are facing increasing pressure from natural and anthropogenic stressors that have already caused significant worldwide declines. In January 2010, coral reefs of Florida, United States, were impacted by an extreme cold-water anomaly that exposed corals to temperatures well below their reported thresholds (16°C), causing rapid coral mortality unprecedented in spatial extent and severity. Methodology/Principal FindingsReef surveys were conducted from Martin County to the Lower Florida Keys within weeks of the anomaly. The impacts recorded were catastrophic and exceeded those of any previous disturbances in the region. Coral mortality patterns were directly correlated to in-situ and satellite-derived cold-temperature metrics. These impacts rival, in spatial extent and intensity, the impacts of the well-publicized warm-water bleaching events around the globe. The mean percent coral mortality recorded for all species and subregions was 11.5% in the 2010 winter, compared to 0.5% recorded in the previous five summers, including years like 2005 where warm-water bleaching was prevalent. Highest mean mortality (15%–39%) was documented for inshore habitats where temperatures were Conclusions/SignificanceThe cold-water anomaly of January 2010 caused the worst coral mortality on record for the Florida Reef Tract, highlighting the potential catastrophic impacts that unusual but extreme climatic events can have on the persistence of coral reefs. Moreover, habitats and species most severely affected were those found in high-coral cover, inshore, shallow reef habitats previously considered the “oases” of the region, having escaped declining patterns observed for more offshore habitats. Thus, the 2010 cold-water anomaly not only caused widespread coral mortality but also reversed prior resistance and resilience patterns that will take decades to recover.背景 珊瑚礁正承受着愈发严峻的自然与人为胁迫压力，此类压力已引发全球范围内珊瑚礁的大规模衰退。2010年1月，美国佛罗里达州沿岸珊瑚礁遭遇极端冷水异常事件，珊瑚暴露于远低于其已知耐受阈值（16℃）的水温中，引发了空间范围与严重程度均前所未有的珊瑚快速死亡。方法与主要结果 该异常事件发生后的数周内，研究团队在马丁县至佛罗里达下礁群区域开展了珊瑚礁调查。调查记录的灾害影响远超该区域此前任何一次干扰事件。珊瑚死亡模式与原位（in-situ）观测及卫星反演得到的冷水温度指标直接相关。此次事件的影响在空间范围与强度上，可与全球范围内广为人知的暖水白化事件相媲美。2010年冬季，所有物种与分区的平均珊瑚死亡率达11.5%；而此前五年夏季（包括2005年暖水白化大面积暴发的年份）的平均死亡率仅为0.5%。近岸生境的平均死亡率最高（15%–39%），该生境的水温条件最为极端。结论与意义 2010年1月的冷水异常事件造成了佛罗里达礁群有记录以来最严重的珊瑚死亡事件，凸显了罕见但极端的气候事件对珊瑚礁存续可能造成的灾难性影响。此外，受影响最严重的栖息地与物种，是此前被视为该区域"绿洲"的高珊瑚覆盖度近岸浅礁生境——这类生境此前曾逃脱了远岸礁生境所经历的衰退趋势。因此，2010年的冷水异常事件不仅引发了大范围珊瑚死亡，还逆转了此前的珊瑚礁抗逆与恢复力模式，而这种模式的恢复将耗时数十年。