Coral and Fish Community Development on Artificial Reefs of Different Ages in Bali:Expectations from Ecological Theory

Many severely degraded coral reefs around the world show no signs of natural recovery, even decades after the disturbances were eliminated. In these degraded reefs the lack of suitable substrate and high post-settlement mortality inhibits coral recolonisation and recovery. In reef sites where the physical structure is lost, restoration efforts aim to provide a fixed substrate, either for natural coral settlement or for the transplantation of coral fragments. Artificial reefs have been designed and developed to be used as a coral reef conservation tool for habitat restoration in disturbed coral reefs. Here, the extent to which an artificial reef can provide a habitat for reef species and support coral recruitment was assessed using a model system of artificial reefs in Bali deployed over six-month intervals for up to 3.5 years. A generally positive trend of coral community development was recorded, including increased coral size, density, cover, and richness on artificial reefs with increasing time since deployment. This change over time can be explained by the facilitation model of ecological theory while metacommunity theory can be applied to explain differences between artificial and natural reef communities. However, fish densities in the artificial reef were significantly lower than in the natural reef, were not significantly different to the adjacent sand sites, and did not change over time. Despite significant differences in coral and fish populations between the artificial reefs and adjacent natural reefs, the trajectory of corals at this stage is encouraging. Previous studies on artificial reefs have estimated it may take between 10-20 years for an artificial reef to re-establish the structure and function of a natural reef. Currently there are no published records describing reef restoration outcomes over such timeframes, making the establishment of this baseline and future long-term monitoring of the artificial reef important contributions to the field