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3, Sep, 2015

Crown of Thorns Sea Star – a beauty misunderstood?

Posted in Fish Finder, Ko Lanta, Latest News, Marine Life, Reef Today by andre

The amazing Crown of Thorns Sea Star

The first time I saw a Crown Of Thorns I had no idea what it was. It was the beautiful blue colour of the arms that first drew my attention. That and its vicious looking spikes. I remember thinking something along the lines of, “Hold your buoyancy! Better not go near that by accident”. I asked my dive instructor about it afterwards and she told me some crazy facts about the Crown of Thorns and sea stars in general. You couldn’t make this stuff up!


Sea star arms and scary shrimps!

The Crown of Thorns is the second largest Sea Star (coming in a close second to the Sunflower Sea Star) and with arms outspread, they can get to a whopping metre in diameter. The arms of these creatures are quite interesting – if sea stars lose an arm they can regrow a new one. This is both amazing and quite useful! If the sea star is threatened by a predator, they can sacrifice an arm to get away and save themselves. Most of their vital organs are located in their arms, so some species can even regenerate a whole new sea star from just one arm and a portion of their central body.

Some predators, such as the Harlequin Shrimp (hymenocera-picta) take advantage of this regenerative super-power and have been known to feed their captured starfish, keeping them alive, so that they can feast on them at a later date!

Harlequin shrip eating Crown of thorns


Inside out stomach for eating

Crown Of Thorns have rows of very sharp spines that work as a defence mechanism and are poisonous. Even if you just touch the spines you will hurt. Crown of Thorns Sea Stars have hundreds of tiny tubular feet on the underside of their body. These tube feet allow the starfish to move along the reef and sandy bottom as they look for food to eat. The Crown of Thorns feeds by a method known as ‘eversion’ where the stomach is forced back out through its mouth and turned inside out, smothering the coral. It then secretes digestive enzymes onto the coral polyps, and starts to absorbs the pre-digested coral-prey, externally.

Crown of Thorns Starfish


Are Crown Of Thorns Starfish good for the Sea and Ocean?

If populations get out of control, Crown of Thorns can eat up entire colonies of coral, so they are not considered good for the sea and the ocean. Over-population can easily cause mass destruction of corals and other marine life.
Even if you try to move them away from munching on delicate and beautiful corals, they will often walk straight back – they can move pretty fast for a starfish. The Crown of Thorns starfish is a nocturnal eater and in just one night it can it its own body weight in coral. This means that an average Crown of Thorns starfish can eat its way through 6-12 square metres of coral reef in just 1 year!

However, although the Crown of Thorns has rather a bad reputation and has even be named ‘The Killer Starfish’, it still plays a crucial and useful role in the delicate balance of the reef ecosystem. The Crown of Thorns starfish eats Staghorn and Plate Corals, which are fast growing hard corals that can overtake a reef if left to grow unchecked. By predominately feeding on the fast-growing corals, the Crown of Thorns can give the slower-growing corals a chance to flourish. Overall, in smaller numbers, the Crown of Thorns is needed to keep the reefs balanced and increase coral diversity.


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