III A Killer Down Under

(taken from National Geo. 8/94 by William Haner)

Jetting through water, a box jellyfish looks as harmless as cotton candy. But this scourge of the beach-also called a marine stinger or sea wasp-is earth's most venomous creature. Contact with its tentacles can bring agonizing death within four minutes.

Shimmering in the glow of flood lamps along the pier, two large ghostly shapes undulate just beneath the surface of the dark sea. Webs of long, almost invisibly thin tentacles swept out behind their box shaped translucent bodies. It was Chironex fleckeri, the infamous box jellyfish found in the near-shore waters of Australia and southeastern Asia.

Difficult to see, these cubic phantoms have long cast a dreadful shadow over the sundrenched beauty of the north Australian coast. Known also as sea wasps or marine stingers, box jellies have killed at least 65 people in the past century. They are the most venomous animals on earth since no other animal's venom can kill a human in 4 minutes or less. Australia's most dangerous snake, the taipan, has enough venom to kill 30 adults, but its bite is not very painful, and it can take several hours for an untreated victim to die. A large box jellyfish, however, has enough venom to kill 60 adults and the pain of its sting is instant and unbearable. Breathing may quickly become distressed as venom is absorbed into the circulatory and lymphatic systems: in some cases, the heart's pumping slows or stops almost immediately.

Trying to study these animals was a task and watching these two large Chironex under the pier, never touching the oyster encrusted pilings that would easily tear their delicate tissue, was a chance to catch these to study their life styles. Using a long-handed net to scoop them up into the waiting buckets, a breeze caught a single tentacle still dangling outside one of the buckets. The collector was stung in the inside of his arm and felt at first he had been branded by red-hot steel. A fiery welt, braided with the characteristic bands of the box jelly's tentacle, appeared. He was lucky as only about an inch of tentacle had struck on his arm. It takes ten feet or more to deliver a fatal dose of box jelly venom.

In order to study the life stages of Chironex, it is necessary to know the life stages of other jellys. Other jellyfish begin their life as mobile little balls of cells called planulae, which settle on rocks or other hard surfaces and transform into polyps--tiny organisms with a crown of tentacles. But in 1977, when the above work was done, no one had ever seen either Chironex planulae or polyps. It was noticed that the stress of capturing them caused them to release their sperm and eggs into the buckets. Using these sperm and eggs released into the bucket, the possibility of getting fertilized eggs was studied to see if the planulae larva and polyps may form.

The biologists soon had tanks, jars, and plastic dishes brimming with planulae but the organisms soon died after transforming into microscopic polyps. It was known the planulae need a solid surface to attach but they rejected all rocks, mollusk shells, coral and mangrove roots offered to them but found the polyps were thriving at the bottom of the tank.

Now that the juvenile forms of the box jelly were identified, the next step was to find them in the wild. This would prove laborious because of their small size and because no one knew where breeding occurred.

Since Chironex medusa appear only in the Australia summer, some biologists thought they migrated south from New Guinea. Others suspected hey might spawn between the mainland and the Great Barrier Reef, some 40 miles offshore.

After months of collecting million of cubic meters of seawater, they found the youngest and smallest medussae were closest to the mainland, indicating their spawning grounds were nearby. Later, Chironex medussae were found three or four miles into such estuaries and streams as Alligator Creek. In 1980 they started collecting mollusk shells and pieces of mangrove roots to examine for polyps under the microscope. After looking for thousands of rocks from 14 rivers for six years, sometimes taking as long as four hours to examine a four inch rock, they finally found a rock with polyps that looked just like Chironex polyps.

Over the next 12 days, the length of time it takes for box jelly metamorphosis, they eagerly watched as each step from polyp to medusa matched what they expected. Finally, when the medusa emerged, they were unquestionably tiny box jellies.

Thanks to their work, we can now describe the entire life cycle of the box jelly. Adults aggregate in river mouths and estuaries in late summer to spawn and then die. The resulting planulae settle onto the bottom, where in the fall they transform into polyps and colonize the undersize of stones, creeping along to find a suitable spot to anchor. During this time, new polyps may sprout from existing polyps. In the spring, the polyps become little medussae, migrating seaward before monsoon rains set in. At sea they feed on prawns and fish, but their favorite food is a small shrimp that schools close to shore--along the same sandy beaches that Australians find so attractive in the summer.

And therein lies the problem. Chironex do not intentionally sting humans, of course, but simply react when their tentacles are brushed. Jellyfish tentacles have specialized stinger capsules called nematocysts, each of which has a mechanical trigger. To fire, however, the nematocysts must be stimulated chemically. That stimulation comes from chemicals found on the surface of fish, shellfish, and unfortunately, humans.

The slowly pulsing translucent bells are hard enough to see as the medusa as the medusa troll for prey in northern Australia's murky coastal waters: their tentacles are even harder to see. Fifteen feet long and only a quarter of an inch thick, they stream behind the bell like invisible fishing lines. In fact, not until 1965, was the species Chironex fleckeri actually described and identified as the creature that inflicted such agony. Stories abounded of swimmers running from the water screaming, tearing at lesions on their skin but never having seen their assailant.

Fortunately for tourism, box jellies don't live on the Great Barrier Reef, where about a million visitors swim throughout the year. Nor do box jellies haunt the beaches of Australia's Gold or Sunshine Coasts near Brisbane. But summer beachgoers have had to adjust their behavior to the presence of the lethal jellyfish along the shores north of the Tropic of Capricorn, which passes near the city of Rockhampton in the northeastern state of Queensland.

When people do bathe along vulnerable beaches, they should either swim in safely netted areas or wear protective clothing. Entrants in surfing competitions have been known to wear 2 pairs of panty hose-one covering the legs, and the other upside down, with the wearer's arms thrust through the pantyhose legs and head poking through a hole in the seat.

How can the ultra thin pantyhose fabric protect against the venom? The stinger capsules are too short to puncture skin covered by the hose. That's fortunate because although each nematocyst injects only a microdrop of venom, a single tentacle contains millions of the deadly capsules.

This is how the box jellies are can be so difficult to treat. Snakes and spiders usually only bite only once in a single spot, but the box jelly venom enters a victim over a large area. There is an anitvenom that was developed 24 years ago by Australia's Commonwealth Serum Laboratories, who injected sheep with non-fatal doses of venom. The sheep produced antibodies that can be used to manufacture antivenom. Medical personnel in coastal regions of the Northern Territory and northern Queensland carry the antivenom.

When injected intravenously, normal breathing often begins immediately, and pain relief usually occurs within minutes. Later scarring is frequently reduced.

Attempts to keep cube jellies in captivity usually fail because they just won't feed in captivity. A new kind of aquarium called a planktonkreisel (plankton carousel) which rotates water in a way to prevent jellyfish from becoming trapped in corners and the drains. As soon as the jellies were put into these aquariums, they began to swim in a circular pattern with their tentacles stretched out behind them--something never seen in still water tanks.

When live shrimp were put into the tank, one of the Chironex's tentacles soon touched a spiny banana prawn, which died instantly. Entangled in the tentacles, the shrimp was reeled in close to the box jelly's pedalium, a feeding appendage that lifted the shrimp up to the medusa's reaching mouth. At last an environment to allow scientists to observe living, feeding box jellies had been developed.

Watching the box jellies eat the banana prawns, it was quickly appreciated why Chironex needs to be so lethal. Prey such as banana prawns are covered with sharp spines which if eaten alive, one flip of their powerful tail would rip the delicate tissue of the jelly to pieces. It is far better to kill quickly.

One observation of the Chironex in the tank was that when room lights were bright and the observer had dark clothes on, moving toward the tank would swim away from that side of the tank. Such behavior in an animal as simple as a jellyfish was unlikely though box jellyfish do have structures that greatly resemble the eyes of vertebrates. Could their nervous system be complex enough to process visual information?

Sealing off the aquarium so that no light penetrated from the outside, various targets were presented to the jelly. Because the target was black to contrast with the white wall of the tank, each time, the jellyfish turned away. These experiments demonstrated that box jellies can see very well, though no one knows how they do it.

After these experiments, the scientists went back to that pier in the beginning of the story. They observed the jellies pulsing toward the pier when three large green turtles appeared. The fastest of the three turtles consumed the jelly in two quick bites.

This creature that can kill in an instant was being casually dined on, tentacles and all, by an enemy obviously immune to its defences. How did the sea turtles do it? Perhaps there is some protection afforded by the lining of their digestive system--which may also be what allows them to eat glass sponges with ease.

So even this most venomous creature has its own vulnerabilities.

Killer Down Under Name....................................pd...........

1. How many people have died in the last century from the BOX jelly stings? (A) 30 (B) 60 (C) 65 (D)4

2. How quickly can cube (box) jelly venom kill a human? (A) several hours (B) 4 minutes or less (C) an hour (D) it doesn't kill

3. How does the venom affect the heart? (A) speeds it up (B) only effects nerve cells not heart (C) slows it down and stops it

4. What is the difference between a planulae and a polyp? (A) planula are mobile and polyps are attached (B) planula are attached and polyps are mobile (C) polyps are adults and planula are larva

5. Where were Chironex medusa found in the wild? (A) close to the mainland (B) in estuaries and streams (C) up to 40 miles offshore (D) a and b are correct (E) b and c are correct.

6. How long does it take for a box jelly to undergo metamorphosis? (A) 12 days (B) 24 days (C) 6 years (D) 4 hours

7. What causes the stinging cells to be triggered? (A) stimulated by temperature changes (B) stimulated by touch only (C) stimulated by chemicals (D) b and c are correct

8. Where in Australia do the box jellies occur in the summer? (A) Gold Coast (B) Great Barrier Reef (C) Sunshine Coast (D) Rockhampton (E) All of these

9. What is a pedalium? (A) tentacles (B) mouth part (C) feeding appendage (D) a live shrimp fed to cube jellies

10. What feeds off box jellies? (A) Asian fishermen (B) sea turtles (C) Great White Sharks (D) Sea Snakes

Darken in the correct answer

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