Large-scale coral reef restoration could assist natural recovery in Seychelles, Indian Ocean

The aim of ecological restoration is to establish self-sustaining and resilient systems. In coral reef restoration, transplantation of nursery-grown corals is seen as a potential method to mitigate reef degradation and enhance recovery. The transplanted reef should be capable of recruiting new juvenile corals to ensure long-term resilience. Here, we quantified how coral transplantation influenced natural coral recruitment at a large-scale coral reef restoration site in Seychelles, Indian Ocean. Between November 2011 and June 2014 a total of 24,431 nursery-grown coral colonies from 10 different coral species were transplanted in 5,225 m(2) (0.52 ha) of degraded reef at the no-take marine reserve of Cousin Island Special Reserve in an attempt to assist in natural reef recovery. We present the results of research and monitoring conducted before and after coral transplantation to evaluate the positive effect that the project had on coral recruitment and reef recovery at the restored site. We quantified the density of coral recruits (spat <1 cm) and juveniles (colonies 1-5 cm) at the transplanted site, a degraded control site and a healthy control site at the marine reserve. We used ceramic tiles to estimate coral settlement and visual surveys with 1 m2 quadrats to estimate coral recruitment. Six months after tile deployment, total spat density at the transplanted site (123.4 +/- 13.3 spat m(-2)) was 1.8 times higher than at healthy site (68.4 +/- 7.8 spat m(-2)) and 1.6 times higher than at degraded site (78.2 +/- 7.17 spat m(-2)). Two years after first transplantation, the total recruit density was highest at healthy site (4.8 +/- 0.4 recruits m(-2)), intermediate at transplanted site (2.7 +/- 0.4 recruits m(-2)), and lowest at degraded site (1.7 +/- 0.3 recruits m(-2)). The results suggest that large-scale coral restoration may have a positive influence on coral recruitment and juveniles. The effect of key project techniques on the results are discussed. This study supports the application of large-scale, science-based coral reef restoration projects with at least a 3-year time scale to assist the recovery of damaged reefs.