Coral restoration is only practical when local human pressure levels are low

Coral reefs are threatened by interacting local (fishing, coastal development) and global (climate change) stressors that degrade coral cover and reduce overall reef biodiversity. Adding coral to the reef (coral restoration) is gaining prominence as a management strategy, however it is unclear whether restoration alone can ensure self-sustaining high coral cover (i.e., > 30% coral cover) under interacting stressors. We assess how much restoration is needed for a self-sustaining healthy coral reef using a mathematical model and real-world restoration case studies. We find that a reef with low macroalgal cover and high coral recruitment requires low levels of restoration to ensure self-sustaining high coral cover. As nutrient enrichment and fishing increase, more restoration is required to ensure self-sustaining high coral cover. Thus, if the reef is facing high local human stressors, restoration is unlikely to ensure self-sustaining high coral cover, suggesting that under such conditions conservation resources should first be allocated towards reducing the impact of stressors, prior to any restoration.