Institute for Biodiversity and Ecosystem Dynamics, Dept. of Freshwater and Marine Ecology, University of Amsterdam, Amsterdam, The Netherlands.
UWA Ocean Institute, The University of Western Australia, Perth, WA, Australia.
PeerJ. 2023 Sep 15;11:e15987. doi: 10.7717/peerj.15987. eCollection 2023.
Coral reefs face an uncertain future punctuated by recurring climate-induced disturbances. Understanding how reefs can recover from and reassemble after mass bleaching events is therefore important to predict their responses and persistence in a rapidly changing ocean. On naturally extreme reefs characterized by strong daily temperature variability, coral heat tolerance can vary significantly over small spatial gradients but it remains poorly understood how this impacts bleaching resilience and recovery dynamics, despite their importance as resilience hotspots and potential refugia. In the macrotidal Kimberley region in NW Australia, the 2016 global mass bleaching event had a strong habitat-specific impact on intertidal and subtidal coral communities at our study site: corals in the thermally variable intertidal bleached less severely and recovered within six months, while 68% of corals in the moderately variable subtidal died. We therefore conducted benthic surveys 3.5 years after the bleaching event to determine potential changes in benthic cover and coral community composition. In the subtidal, we documented substantial increases in algal cover and live coral cover had not fully recovered to pre-bleaching levels. Furthermore, the subtidal coral community shifted from being dominated by branching corals with a competitive life history strategy to opportunistic, weedy corals which likely has implications for the functioning and stress resilience of this novel coral community. In contrast, no shifts in algal and live coral cover or coral community composition occurred in the intertidal. These findings demonstrate that differences in coral heat tolerance across small spatial scales can have large consequences for bleaching resilience and that spatial patchiness in recovery trajectories and community reassembly after bleaching might be a common feature on thermally variable reefs. Our findings further confirm that reefs adapted to high daily temperature variability play a key role as resilience hotspots under current climate conditions, but their ability to do so may be limited under intensifying ocean warming.
珊瑚礁的未来充满不确定性，反复发生的气候诱发干扰时有发生。因此，了解珊瑚礁在大规模白化事件后如何恢复和重新组合对于预测它们在快速变化的海洋中的反应和持久性非常重要。在自然极端的珊瑚礁中，由于每日温度变化较大，珊瑚的耐热能力在小的空间梯度上会有很大的差异，但人们对这如何影响白化抗性和恢复动态的了解仍然很差，尽管它们作为抗性热点和潜在避难所具有重要意义。在澳大利亚西北部的金伯利大区，2016 年全球大规模白化事件对我们研究地点的潮间带和亚潮带珊瑚群落产生了强烈的生境特异性影响：潮间带温度变化较大的珊瑚白化程度较轻，并在六个月内恢复，而亚潮带温度变化适中的珊瑚中有 68%死亡。因此，我们在白化事件发生后 3.5 年进行了底栖调查，以确定底栖覆盖和珊瑚群落组成的潜在变化。在亚潮带，我们记录到藻类覆盖面积大幅增加，而活珊瑚覆盖面积尚未完全恢复到白化前的水平。此外，亚潮带的珊瑚群落从以分枝珊瑚为主的群落转变为以机会主义、杂草丛生的珊瑚为主的群落，这可能对这个新型珊瑚群落的功能和应激抗性产生影响。相比之下，潮间带的藻类和活珊瑚覆盖或珊瑚群落组成没有发生变化。这些发现表明，小空间尺度上珊瑚耐热能力的差异可能对白化抗性有很大影响，并且在白化后恢复轨迹和群落重组的空间斑块性可能是温度变化的珊瑚礁的一个共同特征。我们的研究结果进一步证实，适应高每日温度变化的珊瑚礁在当前气候条件下作为抗性热点发挥着关键作用，但在海洋变暖加剧的情况下，它们可能会受到限制。
