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What is Fire Coral?

Mary McMahon
Updated Jun 04, 2024
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Fire coral is a marine organism in the family Milliporidae which is notable for its stinging cells, which can cause persistent pain to organisms — such as unwitting divers — which come into contact with it. These corals appear in tropical and subtropical waters all over the world, and they can be especially perilous for divers since they appear in a variety of guises. Incidentally, people who are stung with fire coral should use an acid such as vinegar or lemon juice to treat the sting, and if acid is not available, the sting should be flushed with seawater and lightly covered until some vinegar can be obtained.

In strict point of fact, fire coral isn't a coral at all. It is in the are in the same phylum, Cnidaria, as coral, so it is a distant relatives, but they are actually radically different organisms. Fire coral is part of a class of creatures known as hydrozoans, more closely related to jellyfish than true corals.

However, fire corals do share some traits with true corals. They live in colonies which cover themselves in a calcareous skeleton for protection, and they have a symbiotic relationship with algae which is encouraged to grow inside the organism. The algae converts sunlight into energy, and the tiny hydrozoans inside the “coral” use this energy to survive.

The life cycle of fire coral is markedly different from that of true coral. In colonies, the organism takes the form of a polyp, as is the case with coral, and the polyps are capable of reproducing asexually, cloning themselves to expand the size of the colony. The polyps can also bud to create medusas, free-swimming versions of polyps which are capable of sexual reproduction. When medusas reproduce, their offspring can in turn create new colonies.

Fire coral can range in color from yellow to brown, and it takes a variety of forms. Sometimes it takes over, creating a crust on top of rocks and true corals, and it can also grow in plate-like forms and finely branched forms. At a casual glance, this organism often looks like seaweed, so divers may accidentally touch it or swim through it, not realizing the danger. Fire coral is also very hard, and capable of cutting skin and damaging diving suits. People who are cut should seek medical attention, as the wound may need to be cleaned to prevent infection and remove all of the painful stinging cells injected by defensive polyps.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All Things Nature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By PelesTears — On Apr 05, 2011

@parnparsley- you can find plenty of fire coral information on various dive forums on the internet. Everyone reacts to the venom differently so stings can last for days or months depending on the number of times you have been stung and the severity. I have been stung a few times, and it gets better after a few times. I would say to wear gloves, but most places do not want you to wear gloves so that you do not touch the corals.

Fire coral stings are painful, but it is a part of diving. If you are showing signs of infection, you should see a doctor to make sure that you did not pick up an aggressive bacteria (especially in Caribbean and gulf water). Otherwise, time, corticosteroids, and antihistamines are going to be your best friend.

By Amphibious54 — On Apr 04, 2011

@parmnparsley- I am wondering if a hydroid rather than a fire coral stung you. If you compare fire coral pictures to those of certain hydroids, they can look quite similar. They were once thought to be the same species, but they are now known to be less closely related. Hydroids are closely related to jellyfish, essentially a hydrozoa during a certain stage of its development. They are in the same family as the Portuguese man-o-war and they can look like anything from sea ferns to fan corals. They can also attach to seaweeds, dock pylons, mooring ropes, and other underwater surfaces.

The burns are often delayed and they last up to two or three months. The remedies for these types of stings are the same as those for Portuguese man-o-war stings. I read another article on this site that had a discussion about treating jellyfish and Portuguese man-o-war springs. You may want to check some of the other wiseGEEK articles for tips and remedies to help treat hydroid stings after they have occurred.

By parmnparsley — On Apr 03, 2011

How long does a fire coral sting last? I was stung in a beginners dive group off a coral reef in the Caribbean and two weeks later, I still have welts and blisters. Heat seems to make the pain worse (more so initially than now), and it itches and burns like crazy. The blisters and welts also look kind of gross so I wish they would hurry up and heal. Are there any remedies to expedite the healing process?

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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