The status of coral reefs in Rodrigues: 2002 - 2006

Abstract

Coral reef monitoring has been carried out at sites around Rodrigues twice a year since 2002. Initially, 8 sites were monitored, however this has now increased to 13 permanent sites, with 7 sites on the reef flat and 6 on the reef slope. Surveys were undertaken using the Global Coral Reef Monitoring Network methodology to assess benthos, invertebrates and fish. In recent years, water quality was also measured and coral recruitment was  assessed at 3 sites. The results indicate that the reef slope sites were healthy and coral cover was over 50% at half of the sites. Live coral cover has remained stable over the 5 year period however, there were seasonal increases in red macro-algae during October 2004 and  2005. In contrast, sites on the reef flat had a low cover of live coral (<25%), and were dominated by coralline and turf algae. High dead coral was observed in March 2002 and October 2005 and high rubble recorded during March 2003. The fish community at all sites was dominated by Damselfish. Triggerfish, Snapper and Trevally were rare or absent. The fish communities were also dominated by small, undersized individuals. Invertebrates were low on the reef slope sites and most sites were dominated by the bio-eroding urchin, Echinometra mathaei; this species  also dominated the reef flat sites. Molluscs and crustaceans were rare at all sites. Nutrient levels were low;  however nitrate concentration was significantly higher at the two northern reef flat sites. Coral settlement was low, ranging from 0 recruits at Rivière Banane to 1.6 recruits per tile at Passe Armand. The results suggest that although reef slope sites are currently healthy, the reef flats are being subjected to both human and natural  impacts, through coral bleaching, trampling damage and overexploitation. The coral reefs of Rodrigues are    threatened by future coastal developments, population increase as well as climate change and the high numbers of urchins and low levels of coral settlement suggest that the reefs are very vulnerable to degradation. The  Rodrigues Regional Assembly has however approved the creation of a network of 4 marine reserves, and it is  hoped that this will allow damaged sites to recover and protect healthy sites from these future impacts.

Keywords: coral reef, reef fish, sea urchins, Rodrigues, monitoring