An evaluation of artificial reef structures as tools for marine habitat rehabilitation in the Maldives

Abstract

1. In the Maldives, coral mining for the construction industry has resulted in widespread degradation of shallow reef-flat areas. Due to the loss of these coastal resources and the associated problems of coastal erosion, there is an urgent need to find practical methods for rehabilitating mined reefs. 2. The slow rates of natural recovery of mined reefs has prompted interest in the potential of artificial reef structures to rehabilitate these degraded habitats. An experimental artificial reef programme was initiated in 1990 to discover whether it is feasible to use a bio-engineering approach to kick-start natural reef recovery. 3. The main goals of the project were to restore the capacity of degraded reefs for sea defence and their ability to harbour fish species. Accordingly, 360 t of concrete structures of varying levels of topographic complexity, stabilising effect and cost were deployed on a heavily mined study site close to the capital island, Male. 4. Within 1 year of deployment, the artificial reef structures had similar or greater species richness and densities of reef fish than did control pristine reef flats. However, the community structure of the fish populations on the artificial reef structures was significantly different to that on unmined reef flats. 5. Preliminary results of a monitoring programme indicated that substantial coral recruitment had occurred on the larger reef structures which were each supporting ca. 500 colonies, some of which were approaching 25 cm in diameter after 3.5 years. An evaluation of the effectiveness of the various artificial reef structures is discussed in relation to their design features and costs and in line with timescales for the recovery processes.