The impacts of coral bleaching in Rodrigues, western Indian Ocean

Rapid assessments of the degree of coral bleaching were carried out at 22 sites around the coast of Rodrigues during March-April 2005 and April-May 2006. During 2005, coral bleaching was observed at all sites, but the worst affected sites were in the north and west of the island. Bleaching was most severe on the shallow reef flats at depths of 0.5-2m, but also occurred on the reef slopes down to depths of 5-6m. It is suggested that the bleaching occurred due to a combination of high sea temperatures, high solar illumination and exposure. The worst affected species were Acropora spp. and Porites rus; partial bleaching also affected massive coral colonies, soft corals, zoanthids and anemones. No coral bleaching was observed during the 2006 surveys and all sites had recovered from the bleaching except for Totor in the north. At this site, dead standing coral cover was 15% and the site was dominated by turf algae. This site suffered from severe bleaching in 2002 and is also subjected to impacts from sedimentation and trampling, which may account for the mortality. There was a low abundance of coral recruits but a high abundance of the sea urchin, Echinometra mathaei, at this site, suggesting that recovery is limited and that erosion of the reef structure may occur. Rodrigues was also affected by coral bleaching during 2002 and bleaching occurred at other Western Indian Ocean sites in 2002, 2003 and 2004. Rodrigues is a small, isolated island and if coral bleaching events continue to occur on such a frequent basis then this will affect the integrity of the reef structure, leaving the island vulnerable to coastal erosion and storm damage.