Reading - Part 5

Armed and Dangerous

The yacht was anchored 200 meters off the Queensland coast when Chris Slough dived into the water. That's when it got him. "I felt a couple of little stings on my chest," he says, "but I thought nothing of it and carried on." But as soon as he got back on the boat he realized he was in big trouble.

"I suddenly came over very nauseous," he says. Within minutes he was in agonizing pain, vomiting and struggling to breathe. "It felt like my organs were popping out" Chris had been stung by an Irukandji, a vicious creature named after an aboriginal tribe whose folklore tells of a terrible illness that struck people who went swimming in the sea. Irukandji, a species of box jellyfish, grow no bigger than a peanut, yet relative to their size are probably the most toxic creatures on earth, putting many people in the hospital each year with "Irukandji syndrome". All but invisible in the water, their transparent bodies are covered from head to tentacle tip in stinger cells that discharge at the slightest touch, harpooning your skin with venomous barbs. The sting itself is often so mild that you barely notice it until the powerful venom kicks in.

When Chris arrived in hospital, he was given a massive dose of painkillers but no antivenin. Despite the severity and frequency of Irukandji stings, no one has characterized its venom or identified the properties of that of any other species of box jellyfish. In fact, almost everything about box jellyfish is a mystery. Chris was lucky not to have brushed up against chironex fleckeri, a brutish creature the size of a birthday cake with sixty sting-encrusted tentacles.

Jamie Seymour, a tropical biologist at James Cook University in Cairns, has developed a technique for tracking chironex's movements using tiny ultrasonic transmitters stuck on with surgical superglue. True jellyfish are dim-witted ocean drifters, but, the first time Seymour managed to tag a chironex with one of these, it immediately headed straight for the bottom, then suddenly swam off covering nearly half a kilometer in fifteen minutes.

Another remarkable feature of box jellyfish is their visual system. They have twenty- four eyes, arranged in clusters of six, one on each side of their cuboid body. Each cluster contains two types of an eye-four simple light-sensing pits plus two sophisticated "camera eyes". The latter are anatomically similar to human eyes, with lenses, retinas, and corneas, and can form detailed color images, but all this sophisticated equipment begs a question. How do box jellies deal with all the information their eyes gather when they don't have a brain? What happens, for example, when two different eyes are sending out contradictory information? No one knows.

Their predatory eating habits also explain why they have such lethal toxins. It's one thing to stalk fish, but how do you catch them when all you have are flimsy, rubbery tentacles? The answer is to take them out with as much lethal force as possible. A chironex sting certainly does that-its venom can dispatch a fish in less than two minutes. It's just an evolutionary accident that the toxin works so well for us too. Seymour suspects there are more deaths than are officially recognized. He points out that chironex fleckeri was thought to be confined to northern Australian waters but has now been found in Papua New Guinea, Malaysia, Indonesia, the Philippines, Thailand, and Vietnam. The Irukandji too is probably widespread in the Indo-Pacific. "People are getting stung and killed all over the tropics without anybody realizing the true cause," he says.