HORSESHOE

Originally surveyed in 1986, this reef has been surveyed regularly since 1991. Surveys in 1986 revealed an Incipient Outbreak of COTS but subsequent surveys showed COTS to have dropped below outbreak levels on this reef. COTS activity remained below that which would be expected to have a large impact of reef-wide live coral cover over ensuing years. Subsequently there was a small increase in reef-wide live coral cover up until 1995. From this time on COTS activity increased on this reef peaking in 1998 and more recently in 2003. Over this time there has been a corresponding decline in reef-wide live coral cover (due to COTS feeding activity) which is currently low (1-10%) and at the lowest level yet recorded. This reef is currently classified as Active Outbreak. Low levels (generally restricted to a few individual colonies) of bleaching and White Syndrome Disease were recorded from this reef during manta tow surveys in 2003.

Due to increased numbers of COTS, cover of hard coral has declined from 52% in 1997 to 27% in 2000. This decline in cover of hard coral was mainly driven by decreases in cover of the Acroporidae (particularly tabulate Acropora). Consequently there has been an increase in cover of algae on this reef. Cover of soft corals has also decreased by 4% over the survey period. Amongst large reef fishes, the increases in abundance noted for Acanthuridae, Scaridae and Siganidae, mostly reflect peaks in abundance associated with schooling species in either the 1999 and 2000 survey, or both. Certainly the Siganidae result is driven by single schools of S. punctatus and S. corallinus in individual surveys, and the Acanthurid result by schools of Naso tuberosus and Acanthurus blochi in 1999-2000, and 2000 respectivly. However Zebrasoma scopas and Z. veliferum have shown general increases over the period of survey. The curent increase in Labridae results from relatively high abundance for the more common labrids in 2000. Serranidae (Plectropomus leopardus) counts have been variable over the survey period and as such the indicated trend should be viewed with caution. Within the Damselfishes, only Pomacentrus has shown a significant trend with an increase due to highest recorded abundances for P. lepidogenys, P.wardi and P. coelestis in the 2000 survey.

Horseshoe (No. 22-104) is a middle shelf crescentic reef with an area of 12.5 sq.km. Last surveyed September 2002.







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