Research summary

Anthropogenic disturbances have impacted coral reef functioning worldwide, necessitating the implementation of targeted management and restoration strategies. While protective management strategies may effectively conserve functional reefs exposed to less intense and frequent disturbance, coral reef restoration is well-equipped to bolster the future resilience of reefs that have been subject to significant and chronic disturbance in the past. To ensure restoration successfully restores reef function, recent work has recommended conducting restoration in areas less likely to experience high stress, as well as restoring a diversity of coral species and morphologies. As coral reef restoration is a relatively novel field, the current, global scope of restoration efforts and how these activities align with recent recommendations for success is largely unknown. These recommendations are also not currently evidenced quantitatively, necessitation a clearer understanding of the factors determining restoration success. Here, I integrated global datasets of coral cover from >2,000 reefs, coral restoration, human pressures, and climatic variables to identify key gaps in restoration efforts and predict the success of current initiatives given local conditions. Accounting for both stress exposure and background reef habitat, I applied k-means clustering and distance-based ordination methods to identify degraded sites with more stable climates where active restoration could rebuild coral cover and recover ecological function. I also applied a regression tree analysis to identify determinants of restoration occurrence and success, which I then predicted across reefs globally. My results revealed that, rather than targeting offshore reefs with more suitable conditions, restoration is largely occurring near human population centers and in coastal areas exposed to high climatic and local, human-induced stress, which could severely hinder coral survival and restoration success. I also found that restoration success is influenced by local, human-induced pressures and restoration methods, such as the morphologies of restored corals, supporting recommendations to conduct restoration in locations exposed to less stress and restore more diverse coral assemblages. Other determinants of success, such as monitoring time, were likely identified due to limitations in the data and current practices in restoration. Restoration success was predicted to increase at reefs near human population centers, but this finding could also be due to the concentration of restoration efforts near developed coastal areas. Overall, my findings indicate that restoration efforts should (1) shift efforts away from highly stressed reefs that are not suitable for restoration, as well as (2) account for environmental stress and background reef habitat quality when selecting reefs and coral diversity when selecting species to restore. Results from this study can inform a global framework for restoration action that establishes key target regions and reefs where restoration can be used to strengthen coral reef resilience under climate change. In combination with local conservation measures and global action against climate change, effective restoration practices could be key to preserving key coastal ecosystem processes and functions.

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