The Irukandji were an Aboriginal people who inhabited part of the coast of Queensland, in the area of Cairns, until succumbing to the ways of the white man. In the mid twentieth century a mysterious serious illness contracted in those waters was named Irukandji syndrome: backache, headache, nausea, shooting pains, vomiting, sometimes even death. The cause was eventually identified as a tiny jellyfish, only 2 cm across, Carukia barnesi.

As a cubozoan, the Irukandji is a distant cousin of the large, many-tentacled, extremely deadly box jellyfish. That inhabits the inner seas around river mouths, while the Irukandji lives in deeper waters and only occasionally comes shoreward. It has not been implicated in so many deaths, but came to international prominence in recent years with the deaths of several foreign tourists blamed on it. Many more people are treated in hospital each year.

It is a member of the carybdeid group of cubozoans, having only four tentacles, 50 to 500 mm long, one from each corner of its bell. This with its tiny size, and being a jellyfish and all, makes it virtually unnoticeable. Whereas a big box jellyfish attack is instantly the most excruciating pain ever experienced, and you want to die immediately, and you do; the sting of the Irukandji is very slight, does not cause obvious physical damage, and does not take effect until around ten to thirty minutes later. Then, in the middle of nowhere, perhaps unaware of any sting,

the patient develops a complex of systemic symptoms including severe back and abdominal pain, limb or joint pain, nausea and vomiting, profuse sweating and agitation. They may also experience numbness or paraesthesia. Hypertension and tachycardia are frequently seen, and are thought to be related to catecholamine release. Victims frequently require hospitalisation for analgesia and sometimes intravenous antihypertensive therapy; alpha-blocking agents such as phentolamine have been used for this purpose. Supraventricular tachycardia and transient dilated cardiomyopathy have been reported following Irukandji stings, and it has been suggested that serial echocardiography be performed to monitor the progress of severely affected patients. Analgesia is usually required, and may need to be given intravenously when pain is severe. (1)
There is no known cure. Treatment consists of analgesia and "reassurance", i.e. the strongest pain-killers available and being told in a soothing voice that although you think you're going to die, you're not. If you're lucky and the sting wasn't too severe, this will be true.

The species is named after Dr Jack Barnes, who in 1964 potentially sacrificed himself and family to identifying the creature: after capturing one he stung himself, his son, and a volunteer life-saver. They all required hospitalisation, but survived, and it was confirmed that Irukandji syndrome came from this tiny jellyfish.

Although associated mainly with the Great Barrier Reef, the Irukandji jellyfish has been reported from elsewhere in Australian and Indo-Pacific waters. Some Queensland beaches are protected by nets to prevent box jellyfish getting in, but these don't protect against Irukandji. Not much is known about the life cycle of Carukia barnesi, but it is suspected that it is only one of several related jellyfish all of which can cause Irukandji syndrome.

More excellent reasons to be careful paddling near the Reef: blue-ringed octopus, stonefish, poisonous cone shell, sea snake, Portuguese man-of-war, stingray, crocodile.


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