A coral’s enemy: Crown of Thorns starfish (COTS)

What is the crown of thorns starfish?

The crown of thorns starfish (COTS) is the most voracious coral predator found on Indo-Pacific coral reefs. One starfish will eat a coral every day and can consume all of the corals within a 6-10 square meter area within a year.  They are responsible for destroying entire reefs during severe outbreaks. When COTS undergo population explosions, there may be ten COTS per square meter or more, with tens of thousands of animals invading a single reef. They tend to aggregate, piling on top of table corals and wrapping their bodies around delicate branching corals.  Their path of destruction often resembles a forest fire: they spread through a reef devouring the corals as they move and leaving only a few less preferred corals in their wake.


Outbreaks in the Maldives

Coral Reef CPR first began working in the Maldives in 2015 to tackle unnaturally high densities of COTS. This is the third reported outbreak in the Maldives. The first occurred in the 1970s, the second in the early 1990s was slightly larger and more widespread, while the current outbreak is the largest ever witnessed. It began in 2013 in North Malé Atoll; by October, 2015 large numbers of COTS were seen throughout Ari Atoll, two locations on Baa Atoll, one on Lhaviyani Atoll and four locations on South Malé Atoll. Localized but large densities were noted for the first time in 2016 on Shaviyani Atoll.


Why do outbreaks occur?

Excess nutrients: COTS larvae feed on plankton and normal survival rates are very low. When nutrients from sewage, fertilizer and run-off enter the usually nutrient-poor tropical waters, there plankton blooms providing these larvae with more food and their survival rates increase.


Overfishing of predators: Removing the few predators (Napoleon wrasse, pufferfish, triggerfish, trumpet triton) for the food and souvenir trades reduces predation pressure on the COTS, allowing their numbers to increase.

Life-history and biology: COTS are extremely resilient organisms, with a very rapid and successful life-history. They can regenerate their arms and oral discs within 5-6 months; they are highly fecund and one individual can produce up to 60 million eggs per breeding season (once a year); they can last 6-9 months with no food; they can live and move through very deep water (including between atolls!); their bodies are covered in poisonous spines making them less attractive to the few predators.

 What can be done?

Efforts have been undertaken in the Maldives to remove COTS from the reefs and also inject them with chemicals. This can be very successful, but it requires involvement by dive operators, recreational divers, scientists and resort staff and other volunteers. An effected reef requires an initial clean-up, along with follow up collection efforts to remove any missed starfish. Physical removal is very simple and low cost, our team uses a pvc pipe and mecotscollectingsh bag to collect starfish, sending full bags to the surface with an SMB to avoid injury. If injection methods are used, they must be conducted correctly otherwise the starfish can shed the injected limb, re-growing it rapidly. It is also vital that non-toxic substances are used when injecting so collateral damage to the reef is avoided. The only known effective and non-toxic substances are bile salts and vinegar.

Coral Reef CPR has partnered with Carpe Diem Maldives Pvt. Ltd. to detect outbreaks of COTS throughout the Maldives and remove them from affected reefs.

Dive teams of each of the 3 boats have been provided with the education, tools and mesh bags to remove them and will start removing them whenever possible during regular dives and register the information.

During the 10 night trip on the Vita in August 2016, Coral Reef CPR together with the dive team of the Carpe Vita  removed 242 COTs from different sites.


Check back frequently on the Carpe Diem website ( for the total numbers of COTS we have removed!



Coral Reef CPR

Coral Reef CPR joining Carpe Vita Nov. 10/20

Marine biologist from Coral Reef CPR joining again on Carpe Vita November 10/20

Andy Bruckner, Coral Reef CPR Director

The Maldives is known for its megafauna, with annual arrivals of mantas and whale sharks, frequent sitings of pilot, humpback and even blue whales, dolphins, recovering shark populations and an abundance of hawksbill turtles.  The Maldives has over 1190 islands in 26 atolls, and also support more coral reef habitat than anywhere else in the Indian Ocean. In fact, the Maldives has more coral reef than the entire Caribbean Sea and about 3.5% of all shallow water coral reefs found worldwide.  The reef structures are unique and diverse ranging from outer, exposed fore reef communities, steeply sloping walls, and lagoonal reefs (circular faru’s and seamounts known as a thila) influenced by tidal currents, to swift flowing, deep clefts (c20160415-P7260002hannel reefs known locally as a kandu) in the rim of the atoll.  They also support more than 220 species of corals, 1,200 reef fish and thousands of other invertebrates.  Yet for more of these reefs, especially those around the more remote northern atolls, we know very little about their structure, composition or health, or the challenges and opportunities they present.

We do know that coral reefs in the Maldives and also elsewhere on the planet are under severe threat as a result of unusual warmer than normal conditions due to the combined impacts of climate change and the worst El Niño event recorded in history.  Other Pacific and Indian Ocean-wide threats, such as the recent population explosion of the voracious crown of thorns starfish (COTS) place these reefs under further risk.


Coral reef scientists are also aware that the reefs of the Maldives may be doing better than many other locations.  The wide expanses (more than 90,000 square kilometers!) of clean, open ocean water flushes these reefs during the winter and summer monsoons, cooling the reef and bathing it in a nutrient rich plankton soup.  Further, with exception of the densely populated, highly urbanized city of Malé, there are very few people in the Maldives, and very little direct human pressures on the reefs. Fortunately for the coral reefs.

While guests will be enjoying the normal 4 dives a day offered by the Carpe Vita on this part Northern itinerary, we will thoroughly characterize the coral and fish communities, and their health as we did on our previous trip with the Carpe Vita in August 2016. These surveys will allow us to determine how severe the 2016 coral bleaching event was throughout the Maldives , by combining these data with information from our other sites in Central Maldives and our previous visit.  We will also gather valuable information on the spread of the COTS and impacts of these starfish.


COTS first appeared on the west side of North Malé Atoll in 2013, and in 2015 they begin to spread, invading South Malé atoll and Ari Atoll.  Recently, they’ve been spotted on Lhaviyani and Shaviyani Atolls.  Yet, little is known about their abundance, or effects on these reefs.   Whenever we spot a starfish, we’ll collect it to gather additional scientific information on its genetics and also to prevent it from causing more damage on the reef.  In 2015, in about a week, a team of four scientists removed over 7,500 starfish from two reef systems in North Malé Atoll and one in South Malé Atoll, saving these reefs from demise.  We plan to undertake the same effort during this excursion if we identify outbreaks of the starfish, saving the corals while preventing further expansion of the starfish and future outbreaks.

We are extremely excited to partner with Carpe Diem Maldives Fleet and looking forward to working alongside their team to research these reefs and preserve their health! We will be running regular educational seminars during the trip and be available for all questions, no matter the time of day!

For more information on the work of Coral Reef CPR please visit our website ( and if you want to make a difference, why not donate now to help coral reefs of the Maldives (!