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Crown of Thorns Starfish
PhuketDiving - 8/11/2023 8:18 AM
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Crown of Thorns Starfish

The crown of thorns starfish is beautiful to look at but definitely don’t touch

Fortunately Phuket hasn’t got a huge population of crown of thorns starfish. They’re strange appearance and beautiful colours make them great to look at but high numbers can cause immense damage. Their diet of healthy corals and venomous spines don’t place them high on the welcome visitors list which is incredibly unfair. The venomous spines is all on them but destroying coral reefs?
Place Your Hate SOmewhere Else

In a healthy ecosystem they would be just another link in the chain. Human activity has created a number of issues that allow the starfish populations to explode on a more regular frequency than the remaining coral reefs can handle. Overfishing their predators and increased nutrient levels from pollution allow more of the juveniles to reach the adult stage. Coral reefs can naturally recover from the population explosions that have always occurred but struggle when the frequency is exaggerated. So when they do appear in high numbers on reefs already heavily damaged by human activity, panic ensues. This means we have to step in and deal with the problem that we caused. Usually by culling with injections of vinegar.

The good people at the Australian Institute of Marine Science are working on more innovative solutions that hopefully can be used soon.
Prolific Breeders

A single female starfish can release up to 200 million eggs at a time. With the breeding season stretching for months, you can see why numbers can quickly increase. After being successfully fertilised, they drift as larvae feeding on microscopic plants until they’re big enough to settle on a reef. Algae will be it’s diet for up to a year until it reaches its adult form. It can then eat up to 10m2 of coral polyps every year. They reach sexual maturity after 2 years and are ready to start the cycle again.

Just because you can’t see them doesn’t mean they’re not around. Although they can have over 20 arms, grow up to 80cm across and are brightly coloured, they very often hide under rocks and coral heads when they’re not feeding.
Look But Don’t Touch

The spines that can be up to 4cm long don’t inject venom like lionfish for example. They’re covered in a toxic slime that enters the wound from the spine. The toxin as well as being very painful can cause liver damage. If that doesn’t put you off then they can double down and release a cloud of compounds that can destroy red blood cells.
close up of the venomous spines on the crown of thorns starfish

You would think that with this impressive armoury that predators would give the crown of thorns starfish a big swerve. For a long time there was thought to be only a few animals that could eat them, such as triton snails and titan triggerfish (the only thing they’re good for). Recent studies suggest that napoleon wrasse, puffers, groupers and snappers can all stomach the spines and toxins.
If I Get Stung?

Well firstly, you shouldn’t. They’re not fast moving or well camouflaged so you would have only yourself to blame. If you do, it’s not going to be pleasant but highly unlikely to be life threatening (although it can kill mice). The spines should be removed and the wound thoroughly cleaned. If any swelling, pain or redness still persist then professional medical help should be sought. It’s very likely that there are still spines lodged in you which can continue to cause pain and possibly a secondary infection.

We get them on all of our Phuket dive sites so it’s very likely that you’ll encounter one. Just remember as with all our marine life, look but don’t touch.

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