Fire Coral: Look, but do not touch

by B. N. Sullivan

Caribbean fire coral (Millepora alcicornis)When is a coral not a coral? When it is a fire coral.

Fire corals (Family: Milleporidae) look like corals, and that's how they came to be called corals, although some biological characteristics related to their life cycle set them apart distinctly from true corals.

Fire corals are reef builders just like true corals. They secrete a calcareous skeleton. They take on a variety of different shapes ranging from lacy branches (like the example in the first photo on this page), to plate-like structures, to crusts that can cover other things growing on the reef, such as sea fans.

Fire corals and true corals do belong to the same phylum (Cnidaria). A characteristic that all Cnidarians have in common are nematocysts.

Nematocysts are tiny structures on the surface tissue of the organism that are used to capture food, and to defend against predators. Nematocysts actually are very cool structures -- one of nature's engineering marvels. They consist of a fine tube, inside of which is a little coiled thread with microscopic barbs on the end. When something touches the end of the nematocyst it fires the barbed thread into whatever has touched it, just like a little harpoon fired from a harpoon gun.

Red Sea fire coral (Millepora dichotoma)The second photo on this page is an enlarged 1:1 macro shot of fire coral. The little hair-like structures on the surface (called dactylozooids) are armed with the nematocysts. Touching those little hair-like structures triggers the nematocysts to fire. Click on that photo to see an even larger, more magnified version.

The nematocysts of fire corals carry a toxin that is intended to paralyze the minute bits of plankton that are the fire coral's prey. The toxin also causes pain to predators. Divers who touch or even accidentally brush against fire coral, experience a painful sting that burns like all get out -- thus the name fire coral.

Marine biologists who study these kinds of organisms have discovered something that is useful to know. The nematocysts of fire coral (and their first cousins, the hydroids) are de-activated by acids. Thus, it's a very good idea for divers to include in their kits a small container of vinegar when they visit places where they may possibly encounter hydroids or fire coral. A little squirt of vinegar immediately stops the nematocysts that may still be stuck to the skin from firing.

Conversely, fresh water and soapy solutions actually aggravate the nematocysts. The last thing you want to do if you are stung by hydroids or fire coral is to rinse the skin with fresh water. It actually prompts any remaining nematocysts to fire.

If you are ever stung by hydroids or fire coral, you won't forget it. Usually a welt or rash arises immediately and stays for a week or more, burning again every time you take a shower or bath.

For the record, the fire coral in the first image on this page, is Millepora alcicornis, a Caribbean species. It was photographed in the Cayman Islands. The species in the second photo is Millepora dichotoma, photographed in the Red Sea near Sharm El-Sheikh, Egypt.

UPDATE: Here are some more fire coral articles and photos on The Right Blue:

29 comments:

  1. Those little hairs really have a lot of detail! Great info and pics!

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  2. Yes, Kathy, it's those tiny little hairs that you don't want to touch.

    Bobbie & Jerry

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  3. I have heard they pack a lot of punch, but still a great shot.

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  4. The inside of my knee hit a fire coral in Bonaire just a couple of weeks ago. I didn't know what it was at first until someone told me an hour or so later what it was. The sting felt like a ton of bee stings at once. I was told not to rub it, which I had been doing for the previous hour and to put vinegar on it. Which I had none of. So it still itches.

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  5. Hi Anonymous - Don't know if you'll be coming back here to look for a reply, but in case you do -- at this point, if it still bothers you, try some hydrocortisone cream. The kind that you can buy over the counter at a drugstore or Wal-mart should help. If not, you could see your doc and get a prescription for a stronger version.

    Hope this helps. We've been stung by fire coral on a few occasions, and I know how miserable it can be.

    Bobbie

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  6. Just back from Cozumel and a couple of us are now wondering when the welts might go away. Not much burning or itching after 4 days but the 3 spots on the thumb are almost like raised blood blisters. There was contact on the leg as well but it's doing fine. I got closer then normal taking close up pictures. The water might have been great but I will have a dive skin on the next time!

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  7. Hi Anonymous - Fire coral stings are not the kind of souvenir you'd hoped to bring back from Cozumel. Now that the itching and burning has stopped, you probably just need to be patient for the welts to go away, but do monitor them for any sign of infection. Keep the area scrupulously clean.

    We always dive fully covered -- full suits, boots, etc., even in summer. It's all too easy, especially when doing photography, to accidentally brush against fire coral, or hydroids, or the odd stinging jellyfish. And if there's any surge at all, this can amplify the odds.

    Hope your welts disappear very soon. Look after yourself.

    Bobbie

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  8. I was stung by fire coral while snorkeling in Guam while in the Navy in 1976. I fell onto the coral and it cut into my skin. Now, and for the last 10 years, I have a patch of seborrheic keratosis there on my back.
    Does anybody have info on long term effects on the skin from having the nemocists more deeply imbedded in your skin and never doing anything medically about it?

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  9. Look, but do not touch... for certain! We were snorkeling off Jost Van Dyke this New Year and I was unfortunate enough to brush up against Fire Coral. I have a huge welt(s) on my upper thigh. This happened on New Year's Day. After a day or so of agony from the burning, it finally subsided to a annoying itch... then it all but went away. Yesterday morning, I woke to a horrible itching and the welts have come back. The area is hot, red, welted and itches like crazy. Any idea why it would come back like this. Think I'm going to go to the dr. Any feedback would be brilliant. Thanks! Nicola

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  10. Hi Nicola - Sorry to hear about your Fire Coral encounter. It probably would be a good idea to see your doc if the welts persist. Meanwhile, you could try some hydrocortisone cream, which is available over the counter in most places. However, if the welts look like they are infected, do not apply hydrocortisone unless directed by the doctor. In that case your doc may prescribe an antibiotic cream or ointment.

    Fire coral lesions do sometimes last for a long time, unfortunately. Hope yours get better very soon.

    Bobbie

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  11. Hello, I am in the same boat as Nicola. I was diving in Cozmel on February 13th and brushed up against fire coral as I was petting and admiring a sea turtle. Area of my skin stung pretty good when it happened. Dive Master didn't give any indications that I needed to do anything special, so after our next dive, laying on beach, and shopping, we boarded our cruise boat and I took a shower. Initially it was red in a few spots, stung in some others, but didn't see and reaction. A few days went by and it seemed red and raised and then seemed to be almost gone. the 20th, 7 days later, it came back, now I have large red welt's/blisters. Reminds me of when you get pircked by a sticker and it festers. It doesn't have a pus appearance/look infected. Are the spines maybe still in my skin? Has anyone heard of maybe lansing them and trying to squeeze the contents out, maybe if the transparent spine is in there, it will come out? All the web sites I have read state not to wash with fresh water and apply vinegar, well, it's a little late for that. Any help would be appreciated.
    Thanks, Jacqueline

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  12. I just returned from diving in Bonaire, and was actually snorkeling when stung by fire coral. It's been about 10 days since the sting, and it is still red & raised, but doesn't itch or burn anymore. Just looks pretty bad, that and the sand flea bites, not too pretty!

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  13. I was in the Florida Keys, Islamorada, with my family. Two (out of six)of us picked up this orange spongy thing in the shallow water on the ocean side. About 20 minutes later our hands felt like they were full of splinters. We put vinegar on them and it got better slowly of the next day and a half. Now, 9 days later, the two of us woke up to swelling,itchy, hives on our hands.....Is this the same thing coming back???

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  14. Wow, that photo is amazing the detail is so intrege!!

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  15. i am in the same boat like nic and anonymous.. it came back after a week ..itching, burning and looks awful, i ve used antihistamine creams and its not working so what did the doctors tell u after it went back?? when does it completely go away ? doest it come back ever again after months of treatment ? please guys any help

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  16. i ran into coral nearly 3 months ago scrapping my arm and foot a bit. My arm still swells and itches at the site of the scrape. It is not infected but slightly bothersome and looks a bit like eczema? I'm not sure what to do. Will it go away eventually?

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  17. BLUEBOX JELLYFISH DO NOT TOUCH!!!!!!!!

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  18. To anonymous.
    My son had the same thing happen- about 9 days later- course of oral steroids (prednisone) from doctor took it away, but now that he's off steroids, it's coming back- glad to hear he's not alone- but not sure what to do- and we live in AZ- nobody here knows what to do for this, much less even heard of it

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  19. To all of you who have been battling this long term, have you found any solutions to the burning/itching? I have had mine for 4 months, and live in Idaho where they have no experience. I have tried all the over the counter options, high dose steroids and today they did a biopsy of the area, I don't think they're going to find an answer there either, but...so long term care..any options?

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  20. This happened over 40 years ago but, maybe it will help. While making a beach landing (in the South Pacific) I rolled over a broken piece of fire coral with the inside of my right lower leg. There were several punctures where the coral was in bedded in my leg. Didn’t have time to administer any further First-Aid at the time. The fire coral had probably been broken off by a storm the night before our landing. After three days ashore, we made it back to the ship where we found the inside of my ankle from sole of foot to 4 inches above the ankle bone were infected and had turned almost black from blood pooling. The doc who had been stationed at Pearl Harbor prior to this assignment, put me on a powerful broad spectrum antibiotic. (He said when I took it, it would cure my buddies infection. Lol) It all cleared up but then little pieces started surfacing and getting snagged when I would pull on my socks. I would pick out a tiny speck of coral (about twice the size of a large grain of sand) from my leg. This went on for about 3 more years. But all burning and itching stopped after the antibiotic course.

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  21. I'm now scared to go to the Caymen Islands...

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  22. i had a bad encounter with fire coral once, its not actually a coral its more closely kin to a jellyfish, the sting was potent but only hurt me for about 3 days.

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  23. Personally, I never ran into any fire coral in the Caymans. But, I sure did in Bonaire. Wear a LONG wetsuit in Bonaire~

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  24. Could someone reply to the question above asking if its a good idea to pop the raised blisters and look for stingers?

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  25. I got stung by some kind of coral about 4 years ago on the back of my knee and still flares up and itches now! (currently scratching it) my mum has the same problem from the same holiday in Sharme el sheik, is this normal? anything we can do? its annoying, and looks ugly, have white wiggly lines which go dark red when they flare up =S

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    1. I had reactions for about 8 years. Nothing now. Unfortunately I recently got bit by some bed bugs on a trip. Two and half months and everytime I sweat I can see the welts from the bites. That was the same reaction I had with the fire coral. My dermatoligist is working on it and says that my system reacts bad to this type of thing.

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  26. We my gf and I went snorkeling in free port Bahhama's at deadmans reef and she brushed some fire coral with her knee wasn't till reading this we knew for sure it was fire coral thought maybe a jelly fish stinger broke off and had been floating in the water but been two weeks now and she still has a mark that is a dark red and has a corral shape to it!
    Will say we had been drinking. So according to her the pain wasn't to bad and so if you like to drink it will help with the pain lol!
    Just wish we had asked the people that ran our excursion about it so we would have known to put vinegar on it might not have been as bad.
    Any one know if it ever scars? She thinks its gonna scar.

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  27. Hello Anonymous - Sorry your girlfriend had this experience with fire coral. Also sorry to say it may indeed scar, mostly because little tiny bits of the nematocysts (the stinger part of the fire coral) may remain in the scrape. In general, scrapes will scar less if you keep them moist while they heal, e.g. with antibiotic ointment and a covering bandage, but this method seems less effective with fire coral scrapes compared to other scrapes. Worth a try, though.

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We welcome your comments and invite your questions. Dialogue is a good thing!

Bobbie & Jerry