Crown Of Thorns Starfish

Reef Magic Cruises COTS Research Project

The crown-of-thorns starfish Acanthaster planci sp. is a native to coral reefs in the Indo-Pacific. The crown-of-thorns starfish is the most studied starfish in the world, as it eats coral.

On healthy coral reefs, the crown-of-thorns starfish have a functional role, eating the fastest growing corals such as staghorns and plate corals and allowing the slower growing coral species to become more established. This may help increase coral diversity.

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

According to research by the Australian Institute of Marine Science, coral cover on some surveyed reefs have declined by about 50 per cent over the past 27 years. Crown-of-thorns starfish were responsible for almost half of this decline. Cyclone activity along the Great Barrier Reef has also had an effect on coral cover.

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 April, with large females capable of producing up to 65 million eggs over the spawning season.                                                                           

Crown-of-thorns starfish Predators

Predators of adult crown-of-thorns starfish include the Giant Triton Snail, the Maori Wrasse, Starry Pufferfish and the Titan Trigger fish. Predators of the starfish in its younger life stages are less known.

              Starry Pufferfish                                                                                    Titian Triggerfish






                   Maori Wrasse                                                                                  Giant Triton Shell






Reef Magic Cruises is funding a pioneering juvenile crown-of-thorns starfish research project at Marine World. This research includes collecting juvenile crown-of-thorns, recording details such as size and habitat locations and removing juveniles from this site.

This research meets gaps in current knowledge providing essential information on:

  • Spawning
  • Aggregations
  • Movement
  • Habitat
  • Recruitment
  • Growth habitat
  • Coral preference.


The research is starting to provide patterns of recruitment levels. The juvenile crown-of-thorns like to feed on the small diameter branching corals of less than 20mm.





This knowledge has led to another research program where the Australian Institute of Marine Science are pioneering DNA markers for crown-of-thorn starfish larvae. Reef Magic Cruises has provided platforms to conduct time series surveys of crown of thorns starfish larvae presence. Results of this survey are indicating spawning patterns. This information will be essential for management strategies.