It had been a great dive on the USS Spiegel Grove, a large intentionally sunken ship off Key Largo, which is now a popular destination for advanced level scuba divers and all manner of sea critters.

One woman diver probably didn’t think the dive was so great. She ended up sitting near the front of the dive boat madly rubbing ointment on a red rash that covered the upper parts of both her legs.

When diving on the Spiegel Grove, most divers enter the water, pull themselves along a line attached from the boat to the mooring ball line and then descend the mooring ball line — very handy to use when there are currents and for safety stops to vent off nitrogen during ascents.

The downside of this is that some of the mooring lines attached to the Spiegel Grove have picked up a few passengers such as fish hooks and certain types of small fire coral and other stinging critters that can make a diver’s day very unpleasant if grabbed or bumped into by an unprotected arm or leg.

That is what happened to the woman diver. The current pushed her bare legs into the line during a safety stop. Ouch!

Fire corals have nematocysts (barbed, threadlike tubes that deliver a toxic sting) and some have sharp edges that cause lacerations or abrasions.

Over their diving careers many folks, including me, have experienced a sting or burning sensation from accidently touching or bumping into a fire coral. Most of these encounters are unpleasant but the sensation and embarrassment soon subsides.

A person’s reaction to fire coral depends on the amount of exposure to the toxins, extent of the abrasion for a hard coral and any pre-existing sensitivity — like some folks have for bee stings.

In some cases the accidental contact, besides symptoms of immediate stinging and burning, causes more pronounced skin reactions including red welts, blisters, and considerable itching.

The Divers Alert Network — a non-profit organization that provides dive safety information, emergency services, and insurance for the dive community — says it gets about 12,000 to 13,000 information calls each year. The good news is that it only gets approximately a call a week pertaining to someone who has had a run-in with a coral.

Fire corals are hydrozoans, rather than true corals, and are cousins to other hydrozoans such as the Portuguese man-o’-war.

Fire corals, which get their common name from the painful stings they inflict on divers, include colonies composed of tree-like branches, solid colonies that are typically dome-shaped, and colonies that grow on the substrate (surface or material on or from which an organism lives).

Fire corals live at depths up to 120 feet in the Pacific, Atlantic and Indian Oceans and the Caribbean Sea.

According to reef experts Paul Humann and Ned Deloach the three types of fire coral in the Caribbean are branching, blade and box. Another type of coral, lace coral, lacks the “batteries of stingers” of fire coral. Lace corals can irritate sensitive skin but are not considered toxic to divers. The Florida Museum of National History says the branching and blade varieties are found in Florida’s waters.

Fire corals have different appearances. Some grow in small, bubble like patches on other corals. Some look like seaweed. Others grow in thin branches and may have small or large bubble shapes at the end of each branch. Certain fire corals appear like large, stiff leaves.

Reef-building fire corals may appear green, cream, yellow or orange. Species with branches have hollow cores that can be easily broken. Other types of fire coral form thick colonies capable of withstanding the movement of waves.

The stinging cells of fire corals are used to capture prey, which are then engulfed by the corals’ specialized feeding polyps.

Like other coral, fire coral also gets nutrients because of its special relationship with certain types of algae that live on it. The coral gets oxygen and food. The algae get a secure place to live and compounds for photosynthesis (the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water).

Reproduction is more complex in fire corals than other corals. The polyps reproduce asexually (without the union of male and female eggs and sperm) producing jellyfish-like medusa.

The medusa contains the reproductive organs that release eggs and sperm into the water. Fertilized eggs develop into free-swimming larvae that eventually settle on the substrate and form new colonies. Fire corals can also reproduce asexually by fragmentation. (http://www.arkive.org/fire-corals/millepora-spp/)

Fire corals face the same threats as other corals reefs including: poor land management practices that cause the release of sediment, nutrients and pollutants into the oceans; overfishing resulting in the increase of macro-algae; destructive fishing techniques that damage the coral; and, bleaching.

Many types of fire coral are brittle and can be broken by storms and unintentionally by scuba divers. But, sometimes the damage is intentional.

In Brazil, fire coral colonies are extensively damaged when yellowtail damselfish are captured for the aquarium trade. “They are often deliberately smashed and fishes hiding amongst the branches are ‘shaken out’ into plastic bags.” (See earlier site at arkive.org.)

Because fire corals are important to the health of the world’s reefs they are protected in many locations. “All species of stony corals (scientific order Scleractinia), including fire corals (Genus Millepora), as well as sea fans of the species Gorgonia flabellum and Gorgonia ventalina, are protected from take, attempted take, destruction, sale, attempted sale or possession under Florida Administrative Code Rule 68B-4216.” (http://www.dep.state.fl.us/coastal/programs/coral/threats.htm)

All new divers are taught the importance of good buoyancy control to avoid placing their hands or other body parts where they may harm them, ocean creatures or the fragile reef.

But, as occurred to the lady diver at the start of this column, accidents do happen. It is a good idea, even in warm water, to wear a thin protective wetsuit and gloves if holding onto a mooring line is necessary. That said, some dive locations prohibit gloves to discourage touching or holding onto the reef.

There are some first aid treatments if you do happen to get stung by a fire coral.

▪  Rinse the affected area with vinegar or use a paste of baking soda.

▪  Remove any fragments taking care to avoid direct contact with bare fingers or hands – wear gloves or use tweezers if available.

▪  Hot water, heat packs, cold packs or ice may give some pain relief – do not place ice or unheated freshwater directly on affected skin. Rinse again with vinegar.

▪  Certain over the counter cortisone creams may be helpful but, if uncertain, check with a knowledgeable physician or pharmacist before applying the cream

▪  Notify a physician if you have a serious allergic reaction or develop a fever.

▪  Proper cleansing is very important. The most frequent complications from non-stinging coral scrapes are inflammation, which leads to poor healing and possibly a secondary infection.

The Divers Alert Network provides information on first aid for marine life injuries. The organization’s website is: http://www.diversalertnetwork.org/

A quick reference for “The Dos and Don’ts for Treating Aquatic Stings” is: https://www.tdisdi.com/dos-and-donts-of-aquatic-stings/

An on-line source of information on fire corals can be seen at: http://www.arkive.org/fire-corals/millepora-spp/.