We have all seen plenty of them while diving and I’m sure many of you have had the misfortune of having to pick their spines out of your skin at some point. Be it from not looking where you’re walking in shallow water or from brushing up against one while diving, we know they hurt and that we don’t want to get close and for many that’s where we leave it. This week I would like to widen everyone’s knowledge about Sea Urchins!

Sea Urchins Koh Tao

Around Koh Tao we mostly see the Long Spined Black Urchin (Diadema antillarum), which is the most common urchin of all coral reefs. They are herbivores and like to feast on algae that if left uneaten could damage or kill the reef. They spend most of their time hiding in holes in the coral with only their sharp brittle spines exposed as a form of defense. Despite looking so unapproachable they are a favorite food for many creatures including Crabs, Triggerfish and, else where in the world, sea otters. They break off the spines and work there way to the soft center. They are also eaten by people in some countries and considered a delicacy served in a coconut soup.

Whilst there are many creatures, including humans, that would be happy with scoffing down these little creatures after properly preparing them, they are incapable of actively attack us. It is an accident when their spines injure us and while some of them are just painful or cause some irritation or itching, others can have more serious results. In the most extreme cases they can cause a drop in blood pressure, respiratory problems, unconsciousness and in very rare circumstances, death.

A general rule to treat Sea Urchins’ stings is pretty simple.

  1. Remove large protruding spines with tweezers.
  2. Shave the smaller spines or hairs away with a clean razor and shaving cream.
  3. Thoroughly clean with fresh water and soap. Rinse with fresh water after cleaning
  4. Submerge affected area in water as hot as you can handle to ease the pain.
  5. Do not cover with bandages, to allow any remaining spines to work their way out
  6. If redness, swelling or any other signs of infection start add a layer of tropical antibiotic. If infection gets worse consult a doctor
  7. If pain or irritation persist or if spines are deeply imbedded or any sever symptoms start such as shortness of breath, seek medical attention.
  8. If in doubt, play it safe and seek medical attention.

Of course the best thing to do is to just be careful when walking in shallow water and remember to keep good buoyancy while diving. Remember we never want to touch sea urchins or any marine life so as to not harm them or yourself.

Sea Urchin Close Up

On a funnier note this bit in the middle that looks like the sea urchins beautiful eye… Is actually its anus!

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  1. Marine life is not like the terrestrial ones. Most of the land invertebrates are quiet harmless but most sea invertebrates are not. Sea urchins, sea shells, nudibranchs and jellyfishes all can be venomous and deadly. It is because most marine animals are carnivores. That’s why these slow moving creatures like those sea urchins need a solid defense.

  2. Hi,
    I can´t believe, that your Diadema are really antillarum. In the Indo-pacific you may find rather Diadema setosum and Diadema savignyi. Even formerly named Diadema antillarum near the West-African coast are now a species of its own: Diadema africanum.

    Best regards
    willi Clarenbach

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