Résumé
Outbreaks of Acanthaster planci (COTS) in French Polynesia were observed in 1969 and between 1980-1984 where concentrations as high as 110 ind/hectare were observed at Tahiti and Moorea in 1984. Subsequently, outer reef slopes have recovered their preoutbreak percentage coral cover. According to a general survey carried out at the end of 2006, COTS have increased in abundance on islands of both the Society (Tahiti, Moorea, Bora Bora, Raiatea, Huahine) and the Austral archipelagos (Rurutu), but not for the Tuamotu atolls (Manihi, Rangiroa, Tikehau, Fakarava). In order to evaluate the distribution and abundance of COTS at an island scale, a « manta tow » was developed to survey the outer reef slope along the 95 km perimeter of Moorea. This method consists of evaluating feeding marks and after establishing the correlation between feeding marks and COTS abundance, the density of COTS is calculated. Results from 2006-2007 show a mosaic distribution of COTS around Moorea. The outer slope of Moorea, between 10 and 30 m in depth was divided into sectors 250 m long, parallel with the reef crest. Only a few sectors (10 out of 395), mainly on the North and East coasts, show COTS concentrations above 17 ind, which is lower than in 1984. Other sectors show lower concentrations, of which 117 sectors had less than 2 COTS. A comparison of COTS densities between November 2006 and April 2007 does not indicate that the COTS outbreak is progressing. Nevertheless on some sectors with COTS, coral cover, mainly Acropora and Pocillopora, has been reduced by up to 50 %. Future surveys are planned to monitor this event and its consequences