Battle Stations… The COT’s Are Taking Over!

During the weekend of the 14th and 15th of May, our willing volunteers, DMTs and crew members took to the reefs of Tioman in their ongoing battle against the destructive Crown of Thorns Starfish.

Historically, Tioman has had issues with this pesky little critter for a number of years. They’re a natural part of the coral reef ecosystem, but the decrease in their natural predators and other pressing issues has seen their numbers soar to unacceptable levels.

The COTs main predator is the Triton Snail.

Unfortunately, the popularity of the Triton’s beautiful shell in the trinket and souvenir industry has led to rapid reduction in numbers. In Tioman, they are almost non existent.

Studies have also shown that fish feeding has a direct impact on the increase in COT numbers. Throwing bread to the fish changes the dynamics of the ecosystem. Herbivorous reef fish eat the algae that grows on rocks and coral. If inconsiderate snorkellers and snorkel trip operators offer the fish bread, they won’t eat as much of their natural food. This is important because it is thought that while grazing, the herbivorous fish inadvertently consume the larval stage of the COT, actually helping to control numbers. By reducing the grazing, the survival rate of the COT larvae increases and so we end up with more adult COTs eating the reef. So think twice before you buy that bag of roti ikan!

Reduced predators combined with increased pollution have meant that COT numbers can easily get out of control in Tioman. Small numbers of COTs are actually healthy for the reef – think of it like a forest fire making way for new life. However, having too many COTs in a small area overpowers the reef and it loses the ability to recover. This is why we have to take action to keep our beloved reefs healthy.

On Saturday we visited Fan Canyon, Batu Malang and Renggis Island. We’re extremely happy to report that over all the sites, only 3 COTs were spotted. This proves that our continued hard work, along side Tioman Marine Park, Reef Check Malaysia and Cintai Tioman and the other dive operators is making an impact.

However, there’s a site in Tioman that is less dived. We knew that there’s been a COT problem here for a while, and we know that it needs further attention. On Sunday we tackled Last Frontier. In a 50 minute dive, we injected a whopping 32 COTs. In some areas there were 3 or more COTs hanging under one table coral.

Crown of Thorns munching on the coral
The coral destroying Crown of Thorns

It’s easy to spot them – the tell tale bright white trail left on the coral and with a bit of good buoyancy, a peek underneath reveals their location. We use a dry acid solution to inject them. It’s deadly to the starfish, but completely safe to the rest of the reef. We’ve chosen to adopt this method of control, rather than to collect and remove as it’s safer for the diver (no accidental spikes!) plus the nutrients remain on the reef rather than being stuck in some deep smelly hole on land.

We also headed to our adopted dive site at Mangrove Bay to conduct our monthly Dive Against Debris survey. We knew there’s no issue with COTs here, but unfortunately we do have a massive issue with marine debris covering the reefs and root systems of the mangroves. That’s why we adopted this site and pledged to visit it once a month to pay it some very special attention! We removed 9kg of rubbish including glass bottles and tin cans that had obviously been inconsiderately disposed of by fishing boats – “out of sight, out of mind” right??


If you’re interested in taking part in any of our Project AWARE activities then drop us an email. We can even arrange a project for you if you can’t make it for any of our scheduled events.

2 comments on “Battle Stations… The COT’s Are Taking Over!”

  1. Genevieve Hew says: Wednesday July 12th, 2017 at 01:59 PM

    bad thing that the cot’s are taking over.Bad cot’s!!!!!!!!!cot’s are taking over the sea among coral reef. people are feeding fishes in the wrong way .people are treating the sea like a rubbish bin.

    1. B&J Staff says: Thursday July 13th, 2017 at 07:52 AM

      Dear Genevieve,
      We are happy to report that for Tioman we have to COTs pretty much under control. We’ve been doing COT collection since the late 90s and COT injection for the past 10 years very successfully. Get in touch if you’re keen on joining one of our cleanup events!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.