Sunday, 24 October 2010

Crown of Thorns Starfish

Image: Matt Wright
The crown of thorns starfish seems to be less an animal and more a malevolent presence. Starfish are usually odd little things or perhaps just ornamental rocks or something, but the crown of thorns reaches about half a metre across and is a ruthless nocturnal hunter. They can have as many as 19 arms, which for no specific reason I find absolutely disgusting, underneath which are the thousands of tiny tube legs that starfish use to get around. Slowly.

On the upper side of the arms and the entire body is that horrific covering of spikes that lend it its Biblical name. They reach 5 centimetres in length and are sharp. Very, very sharp. On a molecular level in fact, such that they require absolutely no force whatsoever to pierce skin, also wetsuits in case you ever see one. They are also venomous, releasing a neurotoxin that causes pain, nausea and swelling. The spikes can even break off and get embedded in the skin, possibly leading to infection. This is bad enough at home or in your own bed, but in the sea? When all you wanted to do was get up close and personal with the wonders and vibrant colours of the coral reef? That would be disappointing to say the least.

Yeh, also they eat that very same coral reef. They clamber on to corals and use their tube feet to pull their own stomach out through their mouth and all over their food. Enzymes start the digestion process, liquefying the poor coral and allowing the crown of thorns to absorb the result. Something so disgusting probably shouldn't be legal but the crown of thorns seems to really enjoy it, each one can destroy up to 6 square metres (65 sq ft) of coral beauty every year.

It's a good job then that these starfish aren't particularly common, especially since barely anything is capable of eating them, which is understandable. They're solitary animals, usually keeping themselves to themselves (and to coral) and away from others of their own species. I don't know if they realise this, but that is also understandable. In fact, the crown of thorns usually promotes coral diversity by stopping any one type from completely dominating. I did, however, say 'usually'.

Since the 60's there have been some terrible observations of vast numbers of these creatures attacking Pacific coral reefs. They start in one patch and destroy it before moving on, leaving an ever encroaching path of coral skeletons covered in algae and devoid of fish activity. These attacks usually last between 1 and 5 years but can go on for as long as 20 years in particularly large reefs. It is absolute devastation and coral ghost towns can take decades to recover to the extent they were before.

The cause of these population explosions seems to be something to do with high nutrient levels, runoff of agricultural chemicals form nearby land. Overfishing also plays a factor, both of actual predator fish and also of a large, starfish eating marine snail called the Triton which is hunted to sell its beautiful shell. Some people even use poisons to kill or stun fish and the crown of thorns can actually store the same poisons to do the same, meaning they have even fewer predators.

Dealing with the problem is also tricky. People used to just get in their and stab the blighters to death but it turned out that a whole new starfish could regenerate from a severed arm. Remember it has quite a few of those, yikes! These days people inject them with yet more poisons, but carefully selected ones that soon break down in the sea. It's far from ideal, but I guess needs must when you're dealing with the thousands of shuffling tube feet of the zombie march of spiky, poisonous Arma Christi incarnate, bleaching and leeching their way through some of the world's most awe inspiring and biodiverse areas of the world.

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