Our PADI instructors Oleg from Belarus and Nika from Ukraine are our heroes of the week! After discovering the odd crown of thorn starfish while snorkeling along our beautiful house reef we were a little concerned and decided to collect them before their numbers increase.

Here are some interesting crown of thorn starfish facts:

• The abbreviation for Crown of Thorn is COT
• A COT is a large starfish that preys upon hard coral polyps.
• It has venomous thornlike 4cm long sharp spines
• The COT has the same body like a star fish, it starts its life cycle with 5 arms and is later multi-armed
• A COT grows up to 35cm and can have up to 21 arms
• In our region their colour is a beautiful purple blue with red spine tips
• They are very bendy and wrap their arms around the contours of the coral they want to eat
• They prefer branching coral like staghorn and table coral to coral bommies
• To eat, it extrudes its stomach through its mouth over the surface of the coral.
• The stomach secretes digestive enzymes that allow the COT to absorb the nutrients from the liquified coral tissue. This leaves a white scar of coral skeleton behind
• COTs have regenerative powers, if they lose an arm, they can re-grow it

Do not touch
Of course, we do not touch any underwater creature! But be especially careful not to touch this one. If the spine pricks your finger or your toe, it releases some kind of toxin which causes a sharp stinging pain for several hours and swelling for a week. Possible nausea and persistent bleeding due to the blood-thinning effect of the toxins might occur. Also one of its brittle spines could break off and embed itself in your skin, causing an infection.

In healthy numbers, COTs can maintain the coral reef’s biodiversity. They prevent fast growing coral from overpowering the slower growing coral varieties. Of course, an overpopulation of COTs can be dangerous for a coral reef.

The COT has few enemies. In the Red Sea two species of puffer fish been feeding on COTs. The Tritons trumpet is a well know predator. It is a mollusc that has been described as tearing the starfish to pieces with its file-like radula. And a small painted shrimp preys on it.

Overpopulation
Overpopulation has occurred in 21 locations, ranging from the Great Barrier Reef to the Red Sea. 140 – 1000 animal per hectare are considered an outbreak. Studies suggest that over collection of triton shells, overfishing, decline in predators and the increase in COT larvae development due to warmer sea temperatures could be the reasons.

Solution
Injecting sodium bisulfate or common household vinegar into the COT is deadly to the starfish but not to the surrounding reef. This method is more effective as it eliminates 120 COTs per hour per diver. Whereas dismembering or collecting them, as our heroes have done, is less effective, as much fewer individuals can be collected and the risk of being stung is higher. Scientists In Australia developed an autonomous robot called COTSbot. It can seek out COTs and gives them a lethal injection of bile salts.

Our heroes Oleg and Nika collected 4 crown of thorns along our house reef today.