The Crown of Thorns Sea Star (COTS) is known locally in Fiji as “Bula”. It is a large, spiky star with up to 15 legs, which feeds on the live coral animals, leaving white, dead coral skeletons behind it.

These quickly grow over with fuzzy algae, leaving a dead, unattractive piece of reef.

On a natural reef there are animals which would feed on this sea star and keep it in check, but in Fiji many of these animals have been removed by over- fishing or to sell for the tourist trade.

Two Crown of Thorns Sea Stars feeding on the reef
Two Crown of Thorns Sea Stars feeding on the reef

Main natural predators of COTS are;

  • Humphead Wrasse
  • Triggerfish
  • Triton’s Trumpet Shell (Davui)
  • Giant Clams may feed on the larvae when the COTS breed.

COTS feed mostly at night, so you may not see many during the day. Looking for COTS scars (round white patches on corals, or round patches of dead coral on a coral that is alive elsewhere – see photos), will give you a better idea of how many there are, rather than counting actual COTS. However, if you see more than 10 during a 30 minute snorkel, you can assume that they have reached problem levels.

On a reef where there are a lot of scars, look UNDER overhanging corals – that is where they usually hide during the day. They prefer table and branching corals, but will eat boulders too.


Once they are about 30cm across they start to breed and can quickly eat an entire dive or snorkel site. In 1996 / 97 the Mamanucas lost nearly all the branching and table coral to COTS and a new wave is starting now in 2010.

Recommended Removal Programme

Crown of Thorns feeding scars and dead corals caused by COTS
Crown of Thorns feeding scars and dead corals caused by COTS

Remove every COTS seen – do not chop them up and leave them in the water as they can re-grow. I personally do not recommend poisons, as these are difficult to use, expensive, and can also poison the fish. Removal is the best way. Paying a bounty on each one taken out by the community is a very effective way to do it.

One way to remove them is using spears – this works but if the COTS is ready to spawn, she may release up to 10,000 eggs when she is speared.

Recommended – THICK work gloves (leather if possible), LONG barbecue tongs, a rice sack bag for use in the water, and a solid plastic tub to collect
them on the boat.

Pry them off the reef using tongs, drop them in the bag, put into the plastic tub and bring to land. Take them INLAND, away from the beach (they can turn over and crawl back into the sea), tip them out and let them dry up. Burn them or mash for compost.

TAKE CARE WHEN HANDLING (USE THICK GLOVES AND TONGS) – stings should be treated by immersing hand or foot in very hot water for 20-30 minutes and then using antibiotic paste.

Keep the removal programme going until no more are seen – every week if possible, once a month if not.

This may take 1 – 2 YEARS.

Crown of Thorns Sea Star – Recommended Removal Programme for Fiji – download pdf.

Best Practices Guide For Crown-Of-Thorns Clean-Ups

Best Practices Guide For Crown-Of-Thorns Clean-Ups
Best Practices Guide For Crown-Of-Thorns Clean-Ups

Best Practices Guide For Crown-Of-Thorns Clean-Ups

Nicole Fraser, Brian Crawford, And Janny Kusen Proyek Pesisir – Crmp Indonesia

May 2000

Coastal Resources Center, Coastal Management Report #2225

The coral reefs of Indonesia are currently under threat of degradation from both natural and human activities. Human destruction of coral reefs by bomb fishing, cyanide poisoning or anchor damage is now the target of a variety of public awareness campaigns. Natural causes of reef degradation include typhoons, earthquakes, tsunamis, coral bleaching from above-normal sea surface temperatures, and Crown-of-Thorns (COTs) starfish outbreaks. While human causes can be controlled and reversed, natural causes are more problematic. Outbreaks of COTs, however, sometimes offer an opportunity for successful human intervention.

Crown-of-Thorns starfish are naturally occurring organisms on Indonesia’s coral reefs. Their main food sources are corals such as Acropora (karang jari). However, at times the population of COTs exceeds normal levels. Like other biological infestations (for example, locusts infesting paddy fields), COTs outbreaks can cause extremely rapid destruction of an ecosystem (coral reefs) in a matter of months. In recent years, reports of COTs outbreaks have increased. With increased media attention and resulting public awareness, many people now wish to protect the vulnerable, but socioeconomically and biologically important coral reef areas. With responsible intervention, the damage of COTs outbreaks can be decreased by a COTs cleanup, thereby protecting the health of a reef.

This guide is written for anyone concerned about COTs infestations who is considering a COTs clean-up. Information on COTs biology is provided so the potential clean-up team can understand the nature of COTs, lead public education activities on them and be able to answer some of the more common questions. Survey and interview guidelines are provided to determine if a coral reef area is experiencing a COTs outbreak, and whether or not a clean-up is warranted. If so, further information is offered on how to lead a COTs clean-up. This guide concentrates on COTs cleanups in Indonesia and one particular method: physical removal of COTs from the reef and burial ashore. However, each coral reef area is unique and poses a different set of complexities. In addition, each organization’s capacity and resources may vary. The methods detailed in this guide are best practices based on Proyek Pesisir’s experience with COTs clean-ups in North Sulawesi. Potential clean-up teams may wish to adapt or modify these recommendations to meet their specific circumstances.

The goal of a COTs clean-up is to reduce or prevent the damaging impact of COTs outbreaks on a coral reef. Before intervening in any area experiencing a COTs outbreak, it is imperative to recognize that this is a long-term commitment. At least one year (or even longer) may be needed to protect the coral reef area from further COTs damage and to ensure the success of the clean-up. A potential clean-up team must be willing to make this long-term commitment, and be able to secure enough resources (financial and personnel) to maintain a COTs clean-up program for a sufficient period to be effective.

The strategy recommended in this guide for a COTs clean-up follows the seven steps listed below:

  1. Determine whether there is a COTs outbreak.
  2. Decide if a clean-up is needed.
  3. Plan the clean-up.
  4. Conduct the clean-up.
  5. Return to do a post-survey to ascertain the effectiveness of the clean-up.
  6. Monitor the area and undertake additional clean-ups as needed.
  7. Publicize the clean-ups and publish results.

This guide is not meant to be a comprehensive manual on COTs ecology, out breaks, research or clean-ups. Rather, it is to provide basic information, ideas and a framework for making decisions and organizing a clean-up. We encourage sharing any new experience and ideas on COTs clean-ups with us and others. Part or all of this guide may be reproduced for educational puposes or for individuals and organizations unable to obtain an original copy, as long as proper credit is given to the original source. Feedback on the usefulness of this guide (and how it could be improved in subsequent editions) is also welcome.

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