Coral restoration research and technical developments: what we have learned so far

Coral reef restoration is not the same as forest restoration as its success is not always guaranteed because of insufficient knowledge of coral biology. The technology of active restoration has a history of only 40 years or less. In spite of many devices and efforts, restoration is often hampered by low survivorship of colonies, fragments or sexual propagules. In order to enhance coral resilience and adaptation in a changing world, many new approaches to coral reef restoration are being suggested. However, we wouldn't be able to succeed or achieve expected result, i.e. recovery and thriving of the coral reefs, if outplanted coral recruits do not grow well and spawn and successfully fertilize in the sea. The cost to restore a few hectares of reef is often considerable. More studies are needed to improve the methodology. Contractors and practitioners of coral reef restoration projects must have advanced techniques supported by strong science for successful propagation, rearing, and transplantation/outplantation of corals. This review describes what we have learned so far from research on active coral reef restoration and discusses seven topics that may facilitate successful restoration projects.