Hazardous marine species

In short

A few marine species can sting, burn or bite. In almost every case, the incident comes from accidental contact: a hand placed on a rock, a knee in the sand, a jellyfish nobody saw. The best protection is therefore simple: touch nothing and control your buoyancy. This guide presents the main groups of hazardous species by region. It gives no first aid procedure: if you are stung or bitten, get out of the water, tell someone and follow the advice of emergency services.

Why it matters

These animals are not aggressive: they defend or protect themselves. Knowing them lets you watch them safely, recognise the cause of a sudden pain and react without panicking. Intense pain underwater can also cause breathlessness or an ascent that is too fast: knowing what is happening helps you stay calm.

The principle: avoid contact

• Control your buoyancy so that you do not touch the bottom (see the weighting guide).
• Look before placing a hand, a knee or a fin; if you must lean on something, use bare rock only.
• Do not put your hands into holes or under overhangs.
• Wear gloves, boots and a suit to reduce skin contact, without using them as an excuse to touch more.
• Watch camouflaged animals on the bottom from a distance.
• At the surface and when entering the water, look out for jellyfish, especially in summer.

Common species

Scientific names let you find each species in the reference databases listed in the sources.

Jellyfish and relatives (stinging)

• Mauve stinger (Pelagia noctiluca): common in the Mediterranean and the Atlantic, sometimes in large numbers; its tentacles sting badly.
• Portuguese man o' war (Physalia physalis): a bluish float at the surface with long, very painful tentacles; Atlantic and warm seas, sometimes on the French Atlantic coast.
• Snakelocks anemone (Anemonia viridis): stings on contact, especially sensitive skin.
• Fire coral (Millepora spp.): a tropical hydrozoan that looks like a yellow-brown coral; it burns on contact.

Venomous fish

• Weevers (Trachinus draco and related species): buried in the sand in shallow water, in the Mediterranean and the Atlantic; their dorsal spines are venomous.
• Scorpionfish (Scorpaena scrofa, Scorpaena porcus): motionless and camouflaged on rocks in the Mediterranean and the Atlantic; venomous spines.
• Stonefish (Synanceia verrucosa): tropical seas; perfectly camouflaged, its venom is among the most powerful of all fish.
• Lionfish (Pterois volitans, Pterois miles): tropical seas, and now the eastern Mediterranean where they are invasive; long venomous spines.
• Stingrays (Dasyatis pastinaca and related species): a venomous barb on the tail; they defend themselves if cornered or touched.

Spiny or venomous invertebrates

• Sea urchins (Paracentrotus lividus in the Mediterranean, long-spined Diadema spp. in warm seas): their spines break off in the skin.
• Cone snails (Conus spp.): tropical shells; some inject a dangerous venom. Never pick up a cone-shaped shell.

Animals that bite

• Moray eels (Muraena helena in the Mediterranean, Gymnothorax spp. in the tropics): they only bite if you put your hand near their hole or feed them. Keep your distance.

The species present depend heavily on the region; ask at the briefing which hazardous species live on the site.

What to do

Without going into care, which is a matter for emergency services and dedicated training:

1. Signal to your buddy and end the dive, ascending calmly at a controlled speed.
2. Get out of the water and tell the person in charge of the dive.
3. Do not rub the affected area.
4. Call emergency services without delay in case of intense pain, feeling unwell, difficulty breathing, major swelling, an allergic reaction, or if the animal involved is a highly venomous species (stonefish, cone snail, Portuguese man o' war). At sea in France: CROSS on 196 or VHF 16; anywhere in Europe: 112.
5. Follow the instructions of emergency services and your instructors; the rescue guide presents the alert chain.

Key takeaways

• Most incidents come from accidental contact: touch nothing.
• Control your buoyancy and look before placing a hand.
• Beware of camouflaged animals: weevers, scorpionfish, stonefish.
• Never pick up a cone snail and keep your hand away from a moray.
• Stung or bitten: end the dive, get out of the water, tell someone, call for help if needed.

Further reading

In the app's species guide, species flagged as dangerous carry a "Dangerous" badge. Automatic photo identification does not replace caution: an unrecognised or misidentified species may be hazardous. Photos of the main species will be added from the guide image library. The guides on the environment, underwater photography and diving accidents complement this one.