What Is A Crown Of Thorns?

During their time in Malaysia, Nic and James were involved in an ongoing project to reduce the amount of coral destroying Crown of Thorn starfish.

But, what's a Crown of Thorns?

They’re a natural part of the coral reef ecosystem , and they're really beautiful creatures. However, like most beautiful things underwater they're deadly - for 2 reasons.

  1. They're Poisonous!

    You can see the spikes covering the body of the starfish - this is where the creature gets it's name. Each one of those spikes is packed with poison, and you'll know about it if you touch one! Although Nic and James never found themselves on the sharp end, those who have experience extreme pain, nausea and swelling around the puncture site - you'll certainly never touch one again!

  2. They Kill Coral

    COTs eat coral. Especially hard coral - they can't get enough of it. In small numbers this is actually a healthy process on the reef - think of it like a forest fire - it makes way for new growth. Coral is extremely slow growing. Some species only grow 25mm per year, while a COT can annually chomp it's way through 6 square metres of reef! If numbers exceed an acceptable limit, the COTs take over the reef and the coral takes decades to recover.

Why Do The Reefs In Tioman Struggle?

Historically, Tioman has had issues with this pesky little critter for a number of years. A decrease in their natural predators and other pressing issues like pollution has seen the COT population 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 a rapid reduction in numbers. In Tioman, they are almost non existent - Nic and James never saw one on their thousands of dives around the island.

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 feed fish on holiday!

Solving The Problem

It’s easy to spot a COT – they leave a tell tale bright white trail in the coral and with a bit of good buoyancy, a peek underneath the reef reveals their hideyhole. Nic and James trialled a number of control methods during their 4 years in Malaysia. Traditionally, the COTs were collected using a metal hook and placed into a mesh bag. This had a number of health and safety issues including accidental spikes (like the DiveMaster who was so proud of his massive haul, he sat back on the boat and triumphantly placed his mesh bag full of COTs in his lap for everyone to have a look at... that's definitely not somewhere you want to get spiked!) and disposal issues (digging a big hole and dumping them in - smelly and the nutrients aren't returned the reef). 

The best method was injection. A dry acid solution or even just household vinegar are deadly to the starfish, but completely safe to the rest of the reef and the divers using it. Injecting removed the spike risk (as long as you had good buoyancy!) and as the COT is left on the reef, it broke down it entered the food cycle. 

It's Not Just A Problem In Tioman...

Many reefs around the world are under threat from Crown of Thorns. The Great Barrier Reef has huge problems with COTs and coupled with coral bleaching, pressure from tourism and pollution scientists are extremely worried about our valuable reef  systems. 

Although we don't have COTs in the UK, you can still raise awareness when travelling. If you'd like any more information on Crown of Thorns, or to be hooked up on a COT control volunteer programme - get in touch

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