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

Graham et al. (2017) Nature, 518:14140.

Climate-induced coral bleaching is among the greatest current threats to coral reefs, causing widespread loss of live coral cover1.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 change2. Herewe document and predict long-term reef responses to a major climateinduced coral bleaching event that caused unprecedented regionwide 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 fleshymacroalgae. Functional diversity of associated reef fish communities shifted substantially following bleaching, returning towardspre-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.Recoverywas favouredwhen reefswere structurally complex and in deeper water,when density of juvenile corals and herbivorous fisheswas relatively high andwhen nutrient loads were low. Whether reefs were inside no-take marine reserves had no bearing on ecosystemtrajectory. 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 improvedmanagementand adaptation.