Jellyfish of the Great Barrier Reef

Tropical northern Australian waters are home to a number of harmful jellyfish, including the large multi-tentacled deadly box jellyfish Chironex fleckeri and several species of smaller jellyfish known to cause the debilitating Irukandji syndrome.

Box jellyfish

There are almost 30 species of cubozoan or box jellyfish but the lifecycles of only a few are known. In Queensland, they are mainly found in the wet season (November to May) but can be present throughout the year. They are found near the coast as well as near reefs and islands.

The two main groups of cubozoan jellyfish are chiodropids and carybdeids. The Chirodropids include Chironex fleckeri while the Carybdeids include the smaller Irukandji jellyfish. The size of their bodies (known as bells) varies from about 10 mm diameter to 400 mm. Box jellyfish feed on fish, crustaceans and other marine invertebrates. They use potent venom that is injected via a hollow harpoon-like mechanism contained within highly specialized stinging stinging cells. The venom quickly kills the jellyfish’s prey once injected.

Chirodropid jellyfish have multiple tentacles hanging from each of the four corners of their bodies, while carybdeids usually have a single tentacle hanging from each corner. The Chirodropids usually only have stinging cells on their tentacles but most carybdeids have stinging cells on both body and tentacles.

Chironex fleckeri can extend its tentacles to more than three metres in length. Only a few metres of tentacle, which is almost invisible in the water, is needed to contact a swimmer’s exposed flesh to deliver a dose of venom that could be fatal within minutes. It is the most venomous marine creature on the planet and in Australia has killed 70 people in the last 120 years. Most stings occur in shallow water when the wind is light and the water calm. Death occurs rapidly without prompt medical aid.

Irukandji syndrome

An adult Irukandji jellyfish (Carukia barnesi) that periodically infests North Queensland beaches and reefs.

Stings from several species of almost transparent jellyfish may produce a reaction known as Irukandji syndrome – a set of symptoms that often includes severe lower back pain, muscle cramps, vomiting, restlessness and anxiety. These jellyfish are found near tropical islands, beaches and the outer reef. Carukia barnesi, the first jellyfish shown to cause Irukandji syndrome, has been found from Port Douglas in north Queensland to as far south as the Whitsundays.

The mesh used in stinger-resistant nets in north Queensland is fine enough to keep out Chironex fleckeri but may allow Irukandji jellyfish to pass through. Lycra body suits can help protect against stings.

First aid for box jellyfish stings

Should a sting from a box jellyfish occur, assistance should be sought immediately either by calling for a lifesaver, lifeguard or an ambulance. The victim should be removed from further danger when it is safe to do so, and prevented from rubbing and touching the area stung. The area stung should be doused with household vinegar in order to prevent further stings from undischarged stinging cells. Cardio-pulmonary resuscitation maybe required if the victim