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Small medusa spreads sting on east coast

New Zealand Herald.  30 Jun, 2000   03:24 PM

Increasing numbers of swimmers on east coast beaches of the North Island are emerging from the water with an itchy red rash spread over their bodies.

The cause of the rash, known medically as sea-bather's eruption, are tiny creatures called hydromedusae, which get caught inside swimming togs.

People who swim naked tend to be safe, says marine biologist Dr Anita Freudenthal.

Unlike sea-lice, which give a quick, often unfelt bite which affects humans much like a mosquito bite, hydromedusae are a species of jellyfish with tiny stingers and the reaction to their toxins can be painful and debilitating.

Hydromedusae are only about the size of a freckle, are virtually transparent and almost impossible to see.

Dr Freudenthal - whose research identified the problem - said yesterday that the creatures seemed to be multiplying and spreading.


"When I started research here in the mid-90s, reports of sea-bather's eruption were mostly confined to the inner Hauraki Gulf.


Hydromedusae are only about the size of a freckle, are virtually transparent and almost impossible to see.

"The northern limit was around Snells Beach/Arkles Bay and east to Waiheke and Beachlands. Now I'm getting reports from eastern Coromandel and Northland."

The incidence of reports was also growing, possibly because of changes in currents and sea temperatures or in the food supply.

Unlike a sea-lice bite, the stinger toxins could build up in the body, making the effect of the next sting on a sensitised person's skin worse than before, Dr Freudenthal said.

Most people did not notice anything while in the sea but swimsuits that floated loosely around the skin in the water acted as a filter, collecting the tiny nasties.

When swimmers got out of the water the togs clung to their skin and the hydromedusae reacted to the constriction by stinging.

"The best way to avoid being stung is to swim nude," says Dr Freudenthal.

"Failing that, take your togs off instantly once you're out."


Medusae jellyfish.jpg

The tiny jellyfish get trapped inside togs, making them release toxins that can cause itching for up to two weeks

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