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Dr Gerbus Müller, one of SA's foremost toxicology experts, and marine biologist Cameron Ewart-Smith helped us compile this guide to venomous marine creatures – and how to treat the injuries they inflict.
1. Bluebottles
A bluebottle's tentacles contain millions of stinging cells (or nettle cells). If you come into contact with its long tendrils in the waves or on the beach, the venom bags inject poison into your skin through microscopic "needles".
You feel a severe stinging or burning sensation accompanied by itching where the skin came into contact with a tentacle. Red, raised lesions later turn into fluid-filled blisters (these clear up within a day or two).
In extreme cases shortness of breath, nausea, headache, dizziness, an irregular heartbeat, muscle spasms and painful joints may be experienced.
What next?
Rinse the affected area with lots of seawater. Don’t use fresh water (it makes the stinging cells explode) and don't rub the area; it will only cause more irritation.
Scrape the skin with the sharp edge of a knife (or something stiff such as a credit card) to remove the remaining stinging cells. Rinse the skin with vinegar to deactivate the poison. Alcohol and human urine are also effective. Place the affected area in warm (but not boiling) water: heat breaks down the poison.
Seek medical assistance if you experience any of the following: shortness of breath, nausea, dizziness, irregular heartbeat, headache, muscular spasms, joint pains or infection.
Stings from jellyfish and red coral, equally venomous relatives of the bluebottle, can be treated the same way.
Where should you worry?
The entire South African coastline although they're less common along the West Coast.
2. Sea urchins (Echinoidea)
The brittle spines of most sea urchins aren't poisonous but can easily penetrate the skin. Small pieces may remain and become infected. However the long-spined sea urchin (Diadema setosum) found along our coastline is highly poisonous. It's jet-black and has many long spines.
You feel sharp, burning pains and the affected area becomes swollen.
What next?
Place the affected area in warm (but not boiling) water to break down the poison. Use a local anaesthetic or calamine lotion to ease the burning. If you can't remove the spines lodged in the skin get medical help. They cause bumps that have to be surgically removed.
Where should you worry?
Everywhere along our coastline.
3. Sea sponges (Porifera)
The needle-like spines on the surface of sea sponges can cause skin irritation if you rub against them.
You may be stuck with a reddish, itchy rash for a few weeks.
What next?
Apply calamine lotion. See a doctor if the itching doesn't stop.
Where should you worry?
Sea sponges are found in many places along our coastline.
4. Poisonous fish
Some fish such as stingrays, rockfish (Scorpaenidae) including stonefish, devil firefish (Pterois volitans), rabbitfish (Siganidae) and red steenbras use sharp spines and fins to administer their poisons. Most of these fish are well camouflaged and quite passive and some live on the seabed. If you tread on one it releases its poison; pieces of spine can also break off in the skin. The short, thick poisonous spines of the stonefish can sometimes even penetrate the sole of a shoe.
The liver of the red steenbras is poisonous. It's not usually lethal but will cause nausea and stomach cramps if eaten.
You feel a sharp, throbbing pain that can last for hours. Wounds often bleed profusely. In extreme cases nausea, stomach ache, sweating, muscle weakness, fever and convulsions (especially in the case of stonefish) may follow immediately after the injury.
What next?
Rinse the injured area with lots of seawater then place it in warm water (45-50 degrees Celsius) for 30 to 90 minutes – or until the pain subsides – so the heat can break down the poison. If you experience nausea, muscular weakness, stomach ache or convulsions you need to go to a doctor. The spines may need to be surgically removed.
Where should you worry?
All along our coast. Rockfish and stonefish usually stick to shallow water around coral reefs, dense seaweed and rocky areas.
Danger! South Africa's only poisonous sea snake, Pelamis platurus, is black with a yellow stomach and is common along the KwaZulu-Natal coast. Its venom is said to be two to 10 times more poisonous than a cobra's. If you're bitten, get medical help urgently.
There are more friendly fish in the sea...
Don't let bluebottles and sea urchins stop you from enjoying the wonders of the ocean. Many parts of the South African coastline, especially KwaZulu-Natal's North and South coasts, boast abundant marine life.
The area north of Sodwana has beautiful coral reefs hosting brightly coloured tropical fish – even Nemo, which is called a clown fish.
Further north from Mozambique to Kenya and around the Seychelles, Mauritius and Madagascar the colourful underwater scenery is quite breathtaking.
