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Dangerous Marine Life

 Dr Oliver Sykes

Marine life in tropical waters that pose hazards to man can be divided into four general categories: Contact irritants and toxins, Injected toxins, Ingested toxins and Predators . This month I will cover contact irritants and toxins.



All these animals possess nematocysts, a stinging apparatus that discharges on contact. Floating tentacles can retain active nematocysts, even after drying and there is a wide range of toxicity, from mild to severe.

Symptoms: Rapid onset of pain, varying from mild to severe. The rash is red, hot and swollen, usually linear. There is frequent pustule and vesicle formation and severe stings may cause muscle cramps, abdominal pain, fever, chills, nausea, vomiting, respiratory distress, and cardiovascular collapse. Fatalities are increased if there is pre-existing cardiac and respiratory disease. Box jellyfish (aka chironex, irukandji or sea wasp) may cause death in healthy individuals in less than 15 minutes.

Treatment: Use topical vinegar to neutralize undischarged nematocysts or sea water if copious volumes of vinegar are not available and then removal of remaining tentacles. Apply topical analgesics and steroids or intravenous versions if available. Treatment for shock or cardiac arrest may be required and therefore monitoring of pulse and blood pressure is required. Box jellyfish anti-venom is not universally available at all dive sites or smaller hospitals or clinics. Avoiding box jellyfish contact is of paramount importance. When diving in remote resorts in south-east Asia it is wise to ascertain the availability of anti toxin.



This is the only known venomous starfish, its arms having large spines with venom producing integument.

Symptoms: Rapid onset of swelling, redness and pain.

Cleanse the wound and apply topical antibiotics. Give tetanus protection.




Multiple slender spines puncture the skin and break off.

Symptoms: Immediate pain, joint pain, swelling and numbness.

Treatment: Remove spines, cleanse, topical antibiotics and tetanus protection. Soaking in hot water for 60-90 minutes is said to offer relief from the pain and swelling. Surgery is indicated for a foreign body reaction and if a joint capsule is punctured. Topical antibiotics and tetanus protection should be offered.



Some species eject a visceral liquid.

Symptoms: Redness, itching and pain. If eyes are involved, symptoms are similar to chemical burns and blindness can occur.

Treatment: Copious irrigation of the affected area.



Three species of sponges produce a rash on contact, including the red-beard sponge, fire sponge and poison-bun sponge.

Symptoms include: redness, joint pain and swelling.
Treatment: symptomatic with soothing lotions and topical steroids.



Coral may cause abrasions that become infected but there are no toxins associated with coral. Fire coral is not actually coral. It has nematocysts and is more closely related to jellyfish. On close inspection, fire coral has tiny hair like tentacles, unlike coral.



Question 1: What is shock?

Shock is a medical term for poor organ perfusion. The casualty looks pale, has a weak pulse, low blood pressure and may be drowsy or confused. There are many causes of this, but severe decompression sickness, arterial gas embolism, severe bleeding or anaphylaxis are the likely causes in divers. The treatment requires intravenous fluid resuscitation and needs medical support urgently.


Question 2: What is anaphylaxis?

Anaphylaxis is a life threatening reaction which is rare but can occur due/ as a result of to medications, commonly penicillin or stings, such as bee stings. Therefore it is possible to have an anaphylactic reaction to any of the above sea animals. The symptoms come on within minutes of exposure and include wheeze, itching, redness, confusion, drowsiness and shock.


Question 3: How do I treat anaphylaxis?

This may be indistinguishable from a severe jelly fish sting, but the treatment is the same. Therefore remove the cause, apply oxygen and intravenous fluid resuscitation but also adrenaline. People who are known to suffer anaphylaxis often carry adrenaline around with them. Also known as epinephrine, the injection is known as an epi-pen. Steroids, such as hydrocortisone and anti-histamines, such as chlorpheniramine, are used to prevent the reaction recurring. This is a life-threatening condition and patient’s should be taken to hospital for stabilisation or observation if responding to emergency treatment


Question 4: How do I avoid getting stung?

Find out about the dive site beforehand. Jellyfish appear seasonally and most others are rooted to the spot or at least move slowly. The best plan is not to touch anything but a thin wet suit is very effective at preventing stings. Be careful when it comes to washing the suit afterwards, as the nematocysts will still be active!


Question 5: What is Irukandji syndrome?

Irukandji syndrome is similar to anaphylaxis and is produced by a small amount of venom from a box jellyfish. There are muscle cramps, severe pain, a burning sensation in the skin and face, headaches, nausea, restlessness, sweating, vomiting, an increase in heart rate and blood pressure, and psychological phenomena such as the feeling of impending doom. The syndrome is delayed for 5–120 minutes and the treatment is symptomatic, with anti-histamines and anti-hypertensive drugs used to control inflammation and high blood pressure; intravenous opiates are used to control the pain. Irukandji are usually found near the coast, attracted by the warmer water, but blooms have been seen as far as five kilometres offshore. When properly treated, a single sting is normally not fatal, but two people in Australia are believed to have died from Irukandji stings in 2002.


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fire box