Predicting climate-driven regime shifts versus rebound potential in coral reefs

摘要

当珊瑚礁受损时，它们的生态系统会迅速发生改变，以达成一个新的稳定状态。被称为体系转变(regime shift)的这个过程正在全球范围内发生：以前超级多样化的珊瑚现在正受到大型藻类（而不是珊瑚）的支配，从而丧失动物多样性，而且还有可能因此而失去生态系统服务。然而，体系转变并不是普遍性的，而且被扰动的珊瑚礁还能恢复到它们受珊瑚支配的状态。Nicholas Graham及同事采用来自印度洋一太平洋地区21个被扰动珊瑚礁的长期数据对决定一个珊瑚礁是会恢复还是会发生体系转变的因素进行了研究。通过这一自然实验，他们识别出了决定珊瑚礁对某一极端天气事件之反应的相关特征如结构复杂性、水深和鱼类密度等的阈限。这些结果加深了我们对海洋生物多样性所受到的最大威胁之一的认识，并且还有可能使我们先行采取行动来减轻气候变化对热带珊瑚礁的影响。%Climate-induced coral bleaching is among the greatest current threats to coral reefs, causing widespread loss of live coral cover. Conditions under which reefs bounce back from bleaching events or shift from coral to algal dominance are unknown, making it difficult to predict and plan for differing reef responses under climate change. Here we document and predict long-term reef responses to a major climate-induced coral bleaching event that caused unprecedented region-wide mortality of Indo-Pacific corals. Following loss of ＞90% live coral cover, 12 of 21 reefs recovered towards pre-disturbance live coral states, while nine reefs underwent regime shifts to fleshy macroalgae. Functional diversity of associated reef fish communities shifted substantially following bleaching, returning towards pre-disturbance structure on recovering reefs, while becoming progressively altered on regime shifting reefs. We identified threshold values for a range of factors that accurately predicted ecosystem response to the bleaching event. Recovery was favoured when reefs were structurally complex and in deeper water, when density of juvenile corals and herbivorous fishes was relatively high and when nutrient loads were low. Whether reefs were inside no-take marine reserves had no bearing on ecosystem trajectory. Although conditions governing regime shift or recovery dynamics were diverse, pre-disturbance quantification of simple factors such as structural complexity and water depth accurately predicted ecosystem trajectories. These findings foreshadow the likely divergent but predictable outcomes for reef ecosystems in response to climate change, thus guiding improved management and adaptation.