When coral reefs are damaged, their ecosystem can change so radically that a new stable state is reached. This process, known as regime shift, is occurring globally: previously super-diverse reefs are becoming dominated by macroalgae instead of coral, losing animal biodiversity and potentially ecosystem services as a result. Regime shift is not ubiquitous however, and perturbed reefs can also recover to their coral-dominated state. Nicholas Graham and colleagues used long-term data from 21 perturbed reefs in the Indo-Pacific region to examine the factors predisposing a reef to recovery or regime shift. By way of this natural experiment, they identify thresholds for characteristics such as structural complexity, water depth and fish density that predict reef responses to an extreme weather event. These results improve our understanding of one of the greatest threats to marine biodiversity and could enable pre-emptive action to mitigate climate change effects on tropical coral reefs.
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