COTS How To’s


We’ve recently received news that there’s a growing number of crown of thorns starfish (COTS) in Anilao particularly in Koala, Arthur’s Rock, Twin Rocks & Cemetery Beach.

Before doing a COTS clean-up, do determine if there is actual COTS infestation. Crown of thorns starfish in low numbers is crucial in maintaining the number of fast growing hard corals (Staghorn or Acropora spp) which grows abundantly in some areas.

Whenever ocean temperatures and nutrient levels increase, the phytoplankton or algal bloom increases providing food for the developing starfish larvae leading to COTS outbreaks. Major predators that should, under normal conditions, keep COTS populations in check, have suffered from the intense pressures of over fishing.

Among these predators are several Wrasse species (including the Napoleon Wrasse or Mameng), the Giant Triton (Charonia tritonis) and coral polyps themselves – all of which are steadily declining due to illegal collection for the food and aquarium trade.

The COTS are nocturnal and feeds on the coral by everting its stomach and excreting a digestive enzyme onto the coral tissue and then absorbs the digested tissue as it withdraws its stomach. The result is a white scarring of the coral.

How to recognize COTS infestation:

According to WWF CEO Lory Tan, “When diving or snorkeling, look for conspicuous portions in healthy coral heads worn white. Nearby you should be able to spot a COTS, which looks like a cross between a sea urchin and a large grey starfish. Do NOT touch it – for a COT’s long spines are capable of severe stings. Contact will almost surely inflict severe swelling, pain and nausea that can last for hours or days, so be extremely careful.”

How to clean-up COTS properly:

The easiest and cheapest method is by physical removal. Using tongs, pincers or anything similar, gently pry the COTS from the coral head or rock face. Do not cut it up, for its constituent parts may live on. Place all collected COTS in a bucket or holding bin – then dispose of them by fully burying them under the sand just above the high tide level. Utmost care should be taken that the spines of the COTS are not exposed, as they are highly poisonous.

Another method of eradicating COTS is by injecting them with a dry acid or sodium bisulfate. This is very effective and does not produce adverse effects on the marine environment when properly handled.

Normally, reefs should be left alone to deal with unusual occurrences such as this. However, the situation facing Philippine reefs is far from normal. We once had 25,000 square kilometres of coral reef. A recent World Bank study reveals that barely 1% remains pristine and more than 50% are unhealthy.

Everyone going to the beach is encouraged to help clean up COTS infestations – to minimize local damage and support the rehabilitation of our ailing coral reefs. Ultimately, the best response it to keep the reef healthy, stop overfishing, manage sewage and agricultural runoffs, and promote balanced reef biodiversity.

REFERENCE: WWF-Philippines

PHOTOGRAPHY: Paz Santos (Twin Rocks, Anilao)


  1. When do we do the COT clean-up?

  2. Maybe we can do it during Minnie’s check out dive on Aug 25 -26.
    Anyone else interested in joining the COTS clean-up?
    Let’s do garbage clean-up too, I saw lots of floating garbage when I went diving two weeks ago 😦

  3. Game ako diyan …

  4. keep me posted… will try to fix up my sked… want to help out… also i miss diving and of course – you guys… see you soon…

  5. Went diving in Arthur’s Rock yesterday on the third dive of our day trip and we saw lots of COTS. Judging by the number I would say that there’s definite COTS Infestation in the said sanctuary. They are located around 27 – 30 feet, a few meters from the buoy. Judging by the number of COTS we saw, I suggest we do our COTS clean-up earlier, if possible a day trip within the week before the COTS destroys more corals. We were so helpless yesterday and very much unprepared for what we saw. Any volunteers? Dave won’t be available this coming weekend. He has a class scheduled.

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