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Armed and dangerous (Irukandjis, Box Jellyfish)

(New Scientist)


WHEN my friend Chris Slough moved from London to Sydney back in 2000, one of his leaving presents was a book called Dangerous Creatures of Australia. It was supposed to be a joke, but he really should have taken it seriously. Within weeks of his arrival Chris was fighting for his life after being stung by one of the world's most venomous animals, a box jellyfish.

It was the height of summer and Chris and a bunch of friends had hired a yacht to go out to the Whitsundays, a cluster of tropical islands off the coast of Queensland. They were anchored about 200 metres offshore, preparing for the next day's sail when Chris discovered that a rotor under the boat was stuck. So he dived in to fix it. 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 realised he was in big trouble. “I suddenly came over very nauseous,” he says. Within minutes he was in agonising pain, vomiting and struggling to breathe. “It felt like my organs were popping out.”

Chris had been stung by an Irukandji, one of a group of small but vicious box jellyfish that put dozens, sometimes hundreds, of people in hospital each year with so-called “Irukandji syndrome”. Irukandjis grow no bigger than a peanut yet are probably the most toxic creatures on Earth. All but invisible in the water, their transparent bodies are covered from head to tentacle-tip in spring-loaded 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 venom kicks in.

When Chris arrived in hospital he was hooked up to a heart monitor and given a massive dose of painkillers. But the doctors could not give him an antivenin, because there isn't one. Despite the severity and frequency of Irukandji stings, no one has characterised its venom - or indeed that of any other species of box jellyfish. In fact, almost everything about these creatures is a mystery. “We don't even know the basics,” says Lisa-ann Gershwin, a jellyfish expert at James Cook University in Townsville, Queensland.

And Irukandjis aren't the only deadly box jellyfish about which we are woefully ignorant. Chris was lucky not to have brushed up against Chironex fleckeri, a brutish creature the size of a birthday cake with 60 sting-encrusted tentacles. Chironex has killed at least 67 people in Australia since records began in 1883, more than the notorious red back spider. It can kill a grown man in three minutes flat. Yet no-one knows what's in its venom.

It is becoming increasingly clear that our ignorance is creating a public health hazard. Last year, despite extensive measures to keep people and box jellies apart, record numbers of people ended up in hospital with Irukandji syndrome. And, for the first time, there were confirmed deaths from Irukandji stings. In January Richard Jordan, a 58-year-old Briton, died of heart failure after being stung off Hamilton Island. Then in April Robert King, a 44-year-old from Ohio, suffered a fatal brain haemorrhage out on the Great Barrier Reef. It was the “Summer of Sting”.

Rattled by bad publicity in the wake of the deaths, the tourist industry has been pouring money into box jellyfish research. And what the biologists are finding comes as a big surprise. First of all, it turns out that box jellyfish are not jellyfish at all. In fact, it looks as though they have been ploughing a separate evolutionary furrow since the Pre-Cambrian, 543 million years ag0. What's more, the sea is teeming with unknown species. Even a cursory survey has revealed more than a dozen undescribed ones, some probably even more dangerous than Chironex and the Irukandji.

Behaviourally, too, the box jellies are out on a limb. True jellyfish are dim-witted ocean drifters, but these are fast, active predators that hunt and kill prey with incredible speed and brutality. They sleep at night, a behaviour unknown in similarly “primitive” creatures. And they have sophisticated sensory systems including two different kinds of eye. Yet, bizarrely, they have no brain with which to process the information. “They're out there on their own,” says Jamie Seymour, a tropical biologist at James Cook University in Cairns. “Aliens,” adds Gershwin, only half joking.

Seymour is a box jellyfish fanatic who has emerged as the de facto leader of the field. In his view the only way to solve the box jellyfish problem is to learn much, much more about their basic biology. “We know so little about them,” he says. For example, how can you predict when Chironex will cause a hazard when you know next to nothing about its life cycle? Anecdotal evidence suggests that stings usually occur on still, hot days, close to shore on gently sloping, sandy beaches. But this probably tells us more about human behaviour than it does about the box jellies'.

To find out more, Seymour has developed a technique for tracking Chironex's movements using tiny ultrasonic transmitters stuck on with surgical superglue. The experiments are at too early a stage to give more than a snapshot, but they have already revealed some startling facts.

Box jellies have a reputation as strong swimmers. Unlike true jellyfish - which can pulse their bodies weakly to swim up and down in the water column but whose ability to move laterally barely exceeds aimless drifting - they almost never wash up on beaches. But just how dynamic they are came as a surprise. The first time Seymour managed to tag a Chironex, it immediately headed for the bottom. Then it suddenly swam off covering nearly half a kilometre in 15 minutes. A second tagged Chironex bolted straight out to sea and kept going all day. “They're very active. Their metabolic rate is an order of magnitude higher than other jellyfish,” says Seymour.

One simple fact underlies this behaviour: box jellies are voracious predators. “You see chunks of fish inside them,” says Seymour. And drifting around aimlessly is not a good strategy for a fish eater. So the box jellies charge around in search of prey and then unfurl their lethal tentacles, like a trawler chasing shoals of fish before casting its nets. But this highly active lifestyle cannot be sustained 24/7. Which explains another of Seymour's findings - box jellyfish sleep, hitting the sea floor at nightfall and staying put until daybreak. “No one has shown circadian rhythms in a wild jellyfish before,” he says.

And these are not the only unusual findings. One of the most remarkable features of box jellyfish is their visual system. They have 24 eyes, arranged in clusters of six, one on each side of their cuboid body. Each cluster contains two types of eye - four simple pits plus two sophisticated “camera eyes”, anatomically similar to human eyes with lenses, retinas and corneas. The pits are just basic light-sensing organs similar to those found in true jellyfish, says eye expert Dan Nilsson of Lund University in Sweden. But the camera eyes are something else - they can form detailed colour images. Eyes but no brain

Why would a creature so apparently primitive need such sophisticated eyes, and so many of them? Nilsson suspects it's all to do with finding optimum hunting grounds. Seymour agrees they're for hunting, but goes one further. He believes that box jellyfish actively seek out prey. He says he has seen them swim around obstacles and home in on fish.

Whether their hunting techniques are active or passive, 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? Nilsson says that each cluster of eyes has a dense knot of nerve cells behind it, which probably process the visual information. But how it is integrated and leads to appropriate behaviour is anyone's guess. What happens, for example, when two different eyes are sending out contradictory information? No one knows. “An engineer would never design a box jellyfish,” Nilsson says.

The box jellies' high octane predatory lifestyle also affects its digestive system. True jellyfish have a very simple gut consisting of a bag-like stomach with a single opening at the bottom of their “bell” that serves as both mouth and anus. But that would never have enough oomph for a box jelly. They too have a central mouth, but each of their tentacles also contains a tube that acts like a mammalian gut, with a huge surface area for absorbing nutrients. This allows them to obtain energy from their meal with great efficiency before ejecting a puff of waste out of the tentacle ends.

Box jellies' 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 2 minutes. It's just an evolutionary accident that the toxin works so well on us, too.

What exactly is in box jellyfish venom remains something of a mystery. Last year a team led by Ken Winkel of the Australian Venom Research Unit in Melbourne did the first analysis of venom collected from Carukia barnesi, the only species confirmed to cause Irukandji syndrome (see “Box jelly facts”). They found that it contains a potent neurotoxin reminiscent of funnel-web spider venom and some scorpion toxins. But the venom has a mystery component too, which triggers massive release of the fight-or-flight hormone noradrenalin. Winkel's team is now characterising the toxin in more detail and has started work on an antivenin.

But just as research into box jelly venom seemed to be getting somewhere, the question got a whole lot harder. What started out as an attempt to characterise two poisons, Chironex's and Carukia barnesi's, has rapidly escalated to at least 10 with the discovery of new species of box jellyfish. This is largely down to Gershwin. For the past two years, she has been collecting box jellyfish in Australian waters and has discovered 20 new species and counting. “I've barely scratched the surface,” she says. “I think there's a hell of a lot out there.” And many of the new boys look dangerous. Four resemble the brutish Chironex and at least six are probably capable of causing Irukandji syndrome. Gershwin thinks this because she collected them in areas where people were getting sick but there was no sign of Carukia barnesi.

One species in particular stands out. Collected out on the Great Barrier Reef last year, it is a small creature with a pinkish body and bright red tentacles. It looks harmless, but is far from it. Gershwin describes this species as the “baddest dude” in the sea. It has very unusual stinging cells that match those recovered from Robert King's body, leading Gershwin to finger it as the prime suspect in his death. If she's right then the tourist industry has a problem. Conventional wisdom has it that stingers are seasonal, appearing in November and disappearing in May. But Gershwin is finding the pink killer all year round, and some of the other new species also crop up out of season. One of the biggies, for example, only appears in the winter. Unidentified killer

Gershwin, for one, has taken to wearing a protective “stinger suit” all year round. And she is not alone in promoting the view that the stinger problem is being underestimated. Last year's Irukandji deaths were probably not the first, just the first to be recognised for what they were, says Peter Fenner, an expert in Irukandji syndrome at James Cook University's medical school. He believes many people have died but their deaths have been chalked up to other causes such as heart attack, stroke or inexplicable drowning. One death in 1988, for example, was almost certainly down to Irukandji, he says. “And in many places I have lectured I often hear of divers who have been found dead on the beach and a number of so-called drownings.” Gershwin adds: “The symptoms are such that at post-mortem they could easily be mistaken for just about anything, and because Irukandji leaves no physical mark there is no outward sign.”

Seymour, too, suspects there are more deaths than are officially recognised. He points out that Chironex fleckeri was once 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 Irukandjis too are probably widespread in the Indo-pacific. “People are getting stung and killed all over the tropics without anybody realising it,” he says.

With all the new discoveries pouring in, Australians could be forgiven for never setting foot in the water again. But increased awareness is bringing benefits as well. Aside from the antivenin work at AVRU, doctors in Queensland are making progress with a new therapy for Irukandji syndrome. Inspired by a treatment for a form of cancer that also causes a massive release of noradrenalin, it involves infusing magnesium sulphate into the bloodstream. And it seems to work wonders, says Michael Corkeron, a doctor at Townsville Hospital who is leading the clinical trials. Meanwhile, Seymour's group have isolated a compound that seems to stop the stinger cells from firing, and say it could be added to waterproof sunscreen to protect people while they're in the water.

As for Chris, the painkillers worked well enough to let him lie down without it hurting. And he was lucky to have a short bout - it only took 20 hours for him to stop feeling like he was going to die. Three years on he says he feels fine, but the experience has certainly changed him in one way. Nowadays, every time he decides to venture outside the city, he gets out his book on dangerous creatures and starts swotting up.

Box jelly facts

Box jellyfish get their name from the cuboid shape of their bodies. Taxonomists call them “cubozoans”.

Only one species, Carukia barnesi, is known for sure to cause Irukandji syndrome. In 1955 a Queensland doctor called Jack Barnes caught a specimen and stung himself, his son and a lifeguard. All three ended up in hospital. No one has repeated the experiment.

The symptoms of Irukandji syndrome include intense pain, nausea, vomiting, catastrophically high blood pressure and a feeling of impending doom. Victims fall ill as little as 5 minutes after a sting and the symptoms can last for days.

The first thing to do after being stung by a box jelly is to douse the area in vinegar. This stops undischarged stinger cells from firing. Bottles of vinegar are a common sight on northern Australia's beaches.

Irukandji syndrome is named after an Aboriginal tribe whose folklore tells of a terrible illness that struck people who went swimming in the sea.

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