The crown-of-thorns starfish (Acanthaster planci) is the greatest natural threat to coral populations. Outbreaks of the species occur periodically in the Indo-Pacific ocean and lead to the devastation of entire reefs, as is observed in French Polynesia.

The archipelago has been suffering from a new population explosion of the predatory starfish since 2004. It is one of the most intense and devastating outbreaks ever recorded.   The reasons for the outbreak remain unclear, as the causes identified in Australia (excessive rainfall increases nutrients from land-based sinks causing increase in algae) doe not seem to exist.

More information can be found here.