Summertime blues

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Peter Batson

This summer will be remembered by many for the large numbers of stinging bluebottles (Portuguese man-of-war jellyfish) that appeared in the surf and on the shores of many New Zealand beaches.

At the height of the Christmas–New Year holiday break the media ran hot with stories of swarms of abnormally large bluebottles. Reports came from as far south as Otago, although the most spectacular accumulations were seen further north. Thousands washed ashore along the upper west coast of the North Island, having been blown landwards by persistent summer winds.

With 8 cm floats (more than twice the size of normal bluebottles) and tentacles approaching 2 m in length, these big jellies were described in newspaper and television reports as a rare and distinct species, the “Pacific man-of-war.” Their sudden appearance in the shallows off popular swimming beaches soon exacted a significant human toll, with many dozens of stings reported from the Auckland west coast.

The stings were severe by New Zealand standards, often affecting the whole body rather than just a localised patch of skin. In one case a man was rushed to Auckland Hospital with breathing problems, apparently due to an allergic reaction.

Symptoms reported in other cases included chest and stomach cramping, swelling and the inevitable welts where skin had come into contact with tentacles.

Peter Fenner, an Australian physician and researcher on the clinical aspects of jellyfish envenomations, advised against the traditional remedy of applying vinegar to the affected area. Acid can make things worse by causing even more of the bluebottle’s stings to be discharged, he said. Instead, he recom­mended pouring cold, fresh water on to the stung flesh and applying an ice pack.

Were the jellyfish involved in these incidents a new species in New Zea­land’s seas? Phil Pugh, an English expert on world siphonophore jellies (of which the bluebottle is one), thinks not. He believes there is only a single worldwide bluebottle species, Physalia physalis, but that it varies greatly in size. The “Piha monsters” of this summer past are small fry compared to tropical Atlantic specimens, whose floats reach 25 cm across and whose wafting tentacles can be up to 20 m long. Deaths have been recorded in the northern hemisphere from contact with these giants, though probably due to allergic reactions rather than the toxic effects of the venom itself.

Of course, bluebottle tentacles and stings are not designed merely to inflict human misery. Like other jellyfish, bluebottles are predators. On contact with their prey—plankton and fish—bluebottle tentacles discharge thousands of microscopic poison-tipped harpoons called nematocysts. The strength of the poison varies with the species. Bluebot­tle venom is powerful, capable of paralysing fish as large as the jellyfish itself. The nematocysts are used only once—after discharge they are digested along with the prey they helped kill.

Bluebottles are not true jellyfish, although they do belong to the same animal phylum, the Cnidaria, along with sea anemones and corals. They belong to a group called siphonophores, an order of marine gelatinous animals in which each individual is actually a colony of genetically identical, highly specialised animals. The individual units of a siphonophore colony—the zooids—are highly modified for particular tasks: catching food, digestion, swimming or reproduction.

Deep-water siphonophores specialise in catching fish larvae and crustaceans, and their colonies can reach enormous sizes. One species found in New Zealand’s deep sea, Praya dubia, is known to reach lengths of 60 m—more than half the length of a football field. Its colonies, which are far too delicate to survive the violence of coastal waters, resemble a never-ending string of Christmas tree lights and have only ever been seen intact through the viewports of deep-diving submersibles.

Fortunately for New Zealand swimmers, our waters lack the most dangerous jellies: sea wasps or box jellyfish, seasonal residents of large tracts of the tropical Indo-Pacific including northern Australia. The toxin of these transparent jellyfish is ex­tremely virulent, and fatal stings are not uncommon. Death can occur in as little as three minutes after a severe attack. Because of the swiftness of the enveno­mation, it is often difficult to get the patient to a medical facility in time to administer first aid—a problem which contributes to the high death rate.

Sea wasps aren’t the only dangerous Australian species. Earlier in the 2001­2002 summer, the potent stings of another jellyfish, the irukandji, hospital­ised 80 people in Cairns alone.

Not all jellies are nasty. Many species lack the stinging power needed to ruin a day at the beach or even to elicit symptoms. Most of the small to minute jellyfish known as hydromedusae are relatively harmless to humans, although one species found in the northern North Island causes an itchy rash known medically as “sea-bathers eruption.”

Bluebottles pose a much more significant hazard to New Zealand bathers and beachgoers, for they can sting long after washing ashore. Their tentacles are surprisingly strong and elastic, and have an uncanny ability to wrap themselves around arms or legs, even on the slightest contact.

Yet jellyfish, for all the anguish they can cause, are ephemeral creatures, and those encountered in the surf and on the sand are within hours of death, destined to become windblown papery husks. The painful memories of thousands of beachgoing New Zealand­ers will far outlast the agents that caused their misery.

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