Actions to achieve rapid coral self‐attachment: insights from outplanting nails, coral orientation, and substrate biological condition

Abstract

Coral outplanting is a potential method for restoring coral cover in degraded reefs. Rapid coral self‐attachment is key to successful outplanting. Although many technical details have been noted during coral outplanting, it remains unclear how nail type and coral orientation affect the outplanting success. To test the effect of nails and coral orientations on outplanted Acropora intermedia corals over 8 months in Luhuitou Reef, China, three nails (normal, cross, and eta) were selected based on their ability to limit coral movement and combined with two axial corallite orientations (upright and upside‐down). Survival, growth, and especially coral tissue growth on nails or substrates were monitored during the experiment. The survival, partial tissue mortality, and growth showed no significant difference between treatments. However, the ratio of normal nail self‐attachment to the reef substrate was significantly lower than with eta nails. Self‐attachment to the substrate of the upside‐down group was significantly higher than in the upright group. The results have suggested eta nails and upside‐down orientation are most favorable for coral self‐attachment. The sea cucumber Ocnus sanya outbreak at one experiment site gave us the opportunity to study the effects of species interactions on outplanted corals, showing that O. sanya may increase coral tissue mortality by staying at the corals' base and reducing their self‐attachment to the reef. These findings highlight the importance of considering nail type, coral orientation, and substrate biological competition on coral self‐attachment during outplanting.