Population Study Survey of Acanthaster planci, the Crown-of-Thorns starfish on the North-West Coast Moorea, French Polynesia

Outbreaks of Acanthaster planci, the Crown-of-Thorns starfish, have been known to cause considerable amounts of damage to coral reef systems. Surveys of A. planci populations in Moorea, French Polynesia in 2004 indicated the island was experiencing the beginning stages of an outbreak. The goal of the present study was to survey the population densities of these sea stars at 3 sites on the north coast of the island in November 2006. Average densities inside the island’s lagoon were found to be 566 A. planci/ km, while densities on the outer slope were found to be 1352 A. planci/km. These numbers were well above both the outbreak threshold of 30-40 A. planci/km, as well as the population densities measured in the 2004 survey. Data were analyzed to look for a correlation between population densities inside and outside of the reef crest at all 3 study sites. Only the interaction between study site and side of the reef crest was found to be statistically significant. In addition, studies were conducted into the average size and local population density of Acanthaster inside the lagoon as a function of distance from the reef crest. A marginally significant positive correlation was observed for question of average size with distance from the crest. Any measured trend in local population density was determined to be statistically insignificant.