RIB

This reef has been surveyed extensively since 1987. Residual COTS population and large areas of old dead coral indicated that Rib Reef was subject to extremely high COTS populations prior to this time. The reef was classified as Recovering in 1988. Between 1990 and 1994, in the absence of COTS activity, median reef-wide live coral cover increased markedly on this reef from low to high levels (40-50%) where it remained through to 1998. large numbers of COTS were observed on this reef in 1999 and the reef was reclassified as Active Outbreak. Surveys since this time and including our latest survey in 2003 indicate COTS numbers have remained at outbreak levels on this reef and there has been a corresponding drop in reef-wide coral cover to a very low (1-15%) level. Rib Reef remains classified as Active Outbreak. White Syndrome Disease and coral bleaching were recorded from a small number of scattered coral colonies during surveys in 2003.

Detailed coral surveys since 1994 show that cover of hard coral reached a maximum of 68% in 1996. A decrease in cover of hard coral in 1997 was attributed to the impact of Cyclone Justin and in 1999 cover of hard coral averaged 45%. In the past year cover of hard coral has decreased by apporximately 16% and in 2000 averaged 28%. This decline is likely to be due to the presence of COTS, as large populations have been observed on this reef. Declines in cover of hard coral have largely been driven by decreases in tabulate Acropora however despite large reductions in cover, the benthic community on this reef is still dominated by this coral (23% cover) . Cover of all other families average less than 2% in 2000. Cover of hard coral has largely been replaced by turfing algae and cover of this group has increased from 47% in 1999 to 64% in the year 2000. Following cyclone Justin cover of soft corals also declined to approximately half their original levels and no increase has been observed since this time. Cover of soft coral is dominated by the family Xeniidae and now averages 2%. This reef is the only reef in the sector where a similar number of taxa have shown increasing and decreasing trends. A decrease in Acanthuridae is due to the large drop in abundance of Ctenocheatus spp. from a high in 1995-96 to a lower stable level in subsequent years. Chrysiptera. rollandi and C. talboti have both declined to around one fifth of the abundance observed during peaks in 1995-96. Plectroglyphidodon lacrymatus and Amblyglyphidodon curacao have steadily increased over the period of surveys driving the significant trends observed for their respective genera.

Rib (No. 18-032) is a middle shelf crescentic reef with an area of 5 sq.km. Last surveyed March 2003.







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