Assessing techniques to enhance early post-settlement survival of corals in situ for reef restoration

For degraded coral reef systems with limited larval supply, active restoration techniques may provide a means of replenishing adult coral populations. Settling or seeding large numbers of sexually-produced larvae directly onto denuded substrate is a potential restoration tool that can eliminate the costs associated with rearing coral spat in culturing facilities. However, the long-term potential to enhance recruitment using seeding techniques has generally been limited due to high post-settlement mortality. Using the brooding coral Porites astreoides (Lamarck, 1816), we explored two potential strategies-choosing favorable substrate communities and caging recently settled spat-to enhance early post-settlement survival during seeding efforts. Larvae were collected from adult colonies in the laboratory and, once competent to settle, were seeded directly onto the reef substrate. Settled spat were individually mapped and monitored using fluorescence techniques, and found to have a low survivorship with <3%-15% surviving after 1 mo, and <1% after 5 mo. Techniques to enhance survival, including choice of substrate and post-settlement caging, did not significantly influence the high rates of natural mortality. These results underscore the general lack of knowledge regarding the major factors that drive the magnitude of early post-settlement mortality, and future identification of these mortality factors may lead to suitable techniques to enhance survival in seeding efforts.