Crown-of-thorns starfish

The crown-of-thorns starfish (Acanthaster planci) is native to coral reefs in the Indo-Pacific region.

On healthy coral reefs, the coral-eating starfish plays an important role, as it tends to feed on the fastest growing corals such as staghorns and plate corals, allowing slower growing coral species to form colonies. This helps increase coral diversity.

However, outbreaks of this venomous invertebrate pose one of the most significant threats to the Great Barrier Reef.

According to research by the Australian Institute of Marine Science, coral cover on surveyed reefs has declined by about 50 per cent over the past 30 years. Crown-of-thorns starfish were responsible for almost half of this decline.

The research estimates that if crown-of-thorns starfish predation had not occurred over the past three decades, there would have been a net increase in average coral cover.

Cyclic outbreaks of the crown-of-thorns starfish occur approximately every 17 years. There have been four documented outbreaks on the Great Barrier Reef since the 1960s, with the latest starting in 2010. 

To minimise the impact of high numbers of crown-of-thorns starfish, short and long-term strategies are being used to address the current outbreak and minimise the impact of future outbreaks.

Crown-of-thorns starfish spawn during the warmer months (around October to February), with large females capable of producing up to 65 million eggs over the spawning season.

Predators of adult crown-of-thorns starfish include the giant triton snail, the humphead Maori wrasse, starry pufferfish and titan trigger fish. Predators of the starfish in its younger life stages are less known.