Geographically speaking, the Florida Keys are in the Atlantic, but the marine life on these reefs is remarkably similar to that found almost anywhere in the Caribbean. A complex ecosystem supports marine life here including the islands themselves, fringing mangroves, seagrass meadows, patch reef, hard bottom, sand flats and the outer reefs.

HAZARDOUS MARINE LIFE

Fire Coral
The most common dive injury in the Florida Keys is the burning rash caused by contact with fire coral. It can be found — and accidentally touched — nearly anywhere. Fire coral is actually not a true coral but a hydroid colony with a coral-like calcareous skeleton. It comes in two basic forms: leafy fire coral (shaped like mustard brown leaves or ribbons), and encrusting fire coral that can coat structures, ropes or even other coral, such as brain coral or sea fans.

Fire coral stings by discharging small, specialized cells called nematocysts. Contact on bare skin causes a burning sensation that lasts for several minutes and may produce red welts. Do not rub the area, as you will only spread the stinging cells. Cortizone cream can reduce the inflammation and antihistamine cream is good for relieving the pain. Immersing the affected area in hot, non-scalding water may also help. Serious stings should be treated by a doctor.

Jellyfish
Stinging cells called nematocysts are responsible for the pain that jellyfish tentacles can inflict on unwary divers and snorkelers. There are three species of jellyfish to watch out for in the Florida Keys. The Portuguese man-o-war is the most dangerous. The body of this jellyfish floats on the surface, often with the tentacles trailing more than 10ft (3m) into the water. The sting from this jellyfish can be extremely painful, perhaps life-threatening to individuals with allergies.

The moon jelly is often seen along the reef line, floating in the current. They can be found at nearly any depth, but are not particularly dangerous. The tentacles can cause a mild sting or burning, similar to that produced by fire coral.

The upside-down jellyfish is found primarily in shallow water and is most common in Florida Bay. Snorkelers in this area may come into contact with the upside-down jelly while it is lying on the bottom with the tentacles facing up. The sting from this jellyfish is comparatively mild, but should be avoided.

Stings should be treated immediately with a decontaminate such as vinegar, baking soda or a paste made of meat tenderizer. People experiencing a strong reaction may need to be resuscitated and will require immediate medical attention.

Bristle Worms
Also called fire worms, bristle worms are found nearly everywhere on the reef, but are most common in reef rubble zones and seagrass beds. They are also encountered quite often on wrecks. Bristle worms have segmented bodies covered with tufts of sensory hairs that extend in fluffy looking but very sharp bristles. If you touch one, the tiny stinging bristles lodge in your skin and cause a burning sensation that may result in a red welt. Remove embedded bristles with adhesive tape, rubber cement or a commercial face peel. Apply a decontaminant such as vinegar, rubbing alcohol or dilute ammonia.

Sea Urchins
Several decades ago there were thousands of long-spined sea urchins in the Florida Keys, but a Caribbean-wide blight killed most of them in 1987 and the urchins have not yet recovered. That’s not so good for the reef since the urchins helped keep the algae under control, but it’s good news for divers. With far fewer urchins on the reef, it’s much easier to avoid their needle sharp spines.

If you do come into contact with a long-spined sea urchin, the spines will easily penetrate wet suit material and break off in your flesh. Treat minor punctures by extracting the spines and immersing the area in non-scalding hot water. More serious injuries may require medical assistance.

Scorpionfish
These well-camouflaged fish have poisonous spines along their dorsal fins. They lie motionless on the reef or sand, hoping to surprise their prey. Since they are so difficult to see, it’s possible to put your hand, foot or knee on one accidentally if you are not careful with your buoyancy.

Scorpionfish wounds can be exceptionally painful. To treat a puncture, wash the wound and immerse it in non-scalding hot water for 30 to 90 minutes. Seek medical aid if necessary.

Moray Eels
Moray eels have been a favorite with movies and television for years, where they are often portrayed as vicious killers. They do indeed have extremely sharp teeth and strong jaws. They can do a lot of damage in the blink of an eye and even a minor bite by a moray is serious. However, the truth is that you would have to go out of your way to provoke an attack by a moray eel. If you encounter an eel on the reef, keep a reasonable distance and enjoy the moment. It’s always a good idea to keep your hands and fingers away from the eel, since they could be mistaken for small fish.

In the unlikely event that you are bitten, don’t try to pull your hand back quickly — the teeth slant backward and eels have an incredibly strong grip. Let the eel release your hand, then surface slowly. Treat the bite with antiseptics, anti-tetanus and antibiotics and seek medical assistance.

Barracuda
A lot of myths have circulated about barracuda, such as their propensity to attack shiny objects like dive watches or necklaces. The general experience in the Keys is that these fish, like moray eels, are not dangerous to divers and snorkelers unless directly provoked. Fishermen are much more likely to be injured while handling hooked or boated barracuda.

However, barracuda are large, quick predators with an impressive mouthful of very sharp teeth. In addition, they have a habit of closely approaching divers and snorkelers, especially when you first enter the water. Remember that thousands of people swim, snorkel and dive in the Keys every year without being attacked by a barracuda. Keep your hands to yourself, though, because a little caution is never a bad thing.

Irrigate a barracuda bite with fresh water and treat with antiseptics, anti-tetanus and antibiotics.

Sharks
Shark encounters of any kind are actually fairly rare for divers and snorkelers in the Florida Keys. Shark attacks on divers or snorkelers are almost unheard of, and the rare instances usually involve somebody who ill-advisedly grabs a resting nurse shark by the tail.

Sharks will generally not attack unless provoked, so don’t chase, tease or feed them. Avoid spearfishing, carrying fish baits or mimicking a wounded fish, and your likelihood of being attacked will greatly diminish. Quietly face any shark that is acting aggressively and be prepared to push it away with a camera, knife or tank. If someone is bitten by a shark, stop the bleeding, reassure the patient, treat for shock and seek immediate medical assistance.

Stingrays
Identified by its diamond-shaped body and wide wings, the stingray has a venomous spine at the base of its tail. This stinger is primarily a defensive weapon, used by the stingray to discourage an attacker. As with the other fish in this section, unprovoked attacks are exceedingly rare.

There are two common stingrays in the Florida Keys; the southern stingray and the yellow stingray. Southern stingrays are larger and are generally an even gray color. When not feeding or swimming, they tend to bury themselves partly in the sand and rest with only their eyes and gills exposed. Stepping on or attempting to handle a sleeping ray may result in a sting.

Yellow stingrays are smaller, with mottled black and yellow markings. They tend to ignore divers and will calmly continue to search for food right in front of you. Don’t be fooled by their small size. If you harass a yellow stingray, you may get stung.

Though injuries from either species are uncommon, the wounds are always painful and often deep and infective. Immerse wounds in non-scalding hot water and seek medical aid.