Feature

An Erupting Menace

Watch out for the "stingy things" in our waters.

Bruce Bisset

A growing number of children and adults are emerging from the waters of the Hauraki Gulf crying and itching, and as they reach for lotions and ointments to treat the sudden red rash spreading over their bodies, the culprit commonly blamed is sea-lice. But new evidence suggests this much-maligned beastie is not the prime cause. In fact, the cause of what is known in medical circles as "sea-bather's eruption" (to describe the extremely itchy rash) appears to be an almost-microscopic genus of animal known as hydromedusae.

Unlike sea-lice, which give a quick, often unfelt bite which affects humans much like a mosquito bite, hydromedusae are a cousin-species of jellyfish, with tiny cilia around their transparent bodies which deliver a stinging toxin designed to immobilise their zooplankton prey.

"Sea-bather's eruption" therefore is an allergic reaction to the toxins, rather than an infection from a bite, and is best treated in the same way as a jellyfish sting would be; suggestions include applying vinegar, acetic acid or anti-histamines.

Marine biologist and world authority Dr Anita Freudenthal (ex-Long Island University, New York) has been keeping tabs on the proliferation of hydromedusae in the Gulf for the last six years, and while much is unknown about the creatures -- which have a very complex life-cycle for such small organisms -- their numbers seem to be growing and their locations spreading.

"When I started research here in the mid-90's, reports of sea-bather's eruption' were mostly confined to the inner Gulf," Freudenthal says. "The northern limit was around Snell's Beach/Arkle's Bay, and east to Waiheke and Beachlands. Now I'm getting reports from eastern Coromandel and from Northland.

"The incidence of reports is also growing. Whether this has to do with changes in currents and sea temperatures, or changes in the food supply, or some other factor, we don't know as yet. In fact we're not sure whether hydromedusae originate in deeper water offshore, or whether they are emerging from estuaries.

"One thing seems certain -- most people are getting stung on beaches where there is an on-shore wind blowing, so either the wind brings them into the beach or keeps them on the beach," she says. "Certainly the wind concentrates them. Most reports from the Gulf occur when the wind is blowing from the north-east."

The other thing that is certain is that the effects can be extremely painful and debilitating and that -- unlike a sea-lice bite -- the toxins can build up in the body, so that the effect of the next sting on a sensitised persons' skin is worse than before.

The reason most people don't notice anything whilst in the sea is that swimsuits tend to float loosely around the skin in the water, and as water passes through the suit it acts like a filter, collecting the miniature nasties. When you get out of the water the suit clings to your skin, and the hydromedusae naturally react to the constriction by stinging.

"The best way to avoid being stung is to swim nude," says Freudenthal with a laugh. "Failing that, take your togs off instantly once you're out. Even so, I've had people report problems after getting home and taking a shower ... the unnatural freshwater environment also causes them to sting."

Because hydromedusae are tiny (about the size of a small or medium freckle) and virtually transparent (some have a tiny black or red spot inside them) they are almost impossible to see. You may catch a glint of sunlight as one moves, but otherwise it takes a microscope to examine them.

The uncomfortable rash caused by hydromedusae is most pronounced in areas where the bather's swimming costume clings to the skin, such as the buttocks and side of the torso.

The Hunt for the Culprit

Freudenthal has been working on identifying the causes of "sea-bather's eruption" for 20-odd years. In fact she was the first person to discover a cause for the rash, which was first classified and given its distinctive name by a Florida physician in 1949, but which stumped successive researchers for 30 years afterward as to cause.

"One day in 1980 I got a call from a lifeguard on the southern coast of Long Island with 200 people with this problem," she says. "I thought it was what the Caribbeans call sea-lice and the Europeans call Caribbean Itch, but the medical people said it looked like a classic case of sea-bather's eruption', previously unknown in the area. Soon thousands of people had been affected.

"I did some research and determined the causative organism was the larvae of sea-anemones! Later I went down to Florida where they had long had a similar problem, but there it was from the larvae of jellyfish.

"On Long Island the problem was always on the south side, which is washed by the Atlantic, while the north side is virtually land-locked. Then one year I got a call from the north side, and all I could find in the sample was hydromedusae.

"I dismissed this at the time, but a couple of years later we (Freudenthal's husband, Hugo, is also a renowned marine biologist specialising in work with coral) holidayed in New Zealand and I heard about a similar problem here. No-one knew what it was.

"When we came back in 1996 I started doing some serious sampling, looking for larvae, but again all I could find were hydromedusae. As more and more data build up each summer, finally the penny dropped." She says all these organisms are related, but that the many different species of hydromedusae are not a larval stage when they sting, merely at one stage in a complex life cycle. They have little barbs that deliver their poison like a needle, and most of the people affected by them are those more prone to allergies.

Their sting-cells have developed because they eat zooplankton rather than phytoplankton (animal rather than plant) -- again unlike sea-lice, which eat phytoplankton. While they are tiny animals, the sometimes-severe effect of what is a minute dose of poison demonstrates how powerful it is; and there is one deadly species around Great Barrier Reef in Australia that can kill a human in about four minutes!

Children are most commonly affected because their skin is soft and sensitive -- suntanning helps harden the skin and prevent the rash -- and kids also play in the shallows where the hydromedusae are presumed to concentrate.

Looking like some miniature alien spaceship, hydromedusae float unnoticed, for the most part, in our coastal waters.

Research Required

Freudenthal says that while Auckland Healthcare have provided some funding for medical students to undertake sampling programmes on her behalf, in essence all the research to date has been done for free. What is now needed is a properly-funded scientific study to test the various theories which she has developed as a result of her researches.

"I'd love to get funding for a student to do a PhD thesis, and we need a solid network of sampling, better reporting procedures and public education. The data needs to be computer analysed -- at the moment the analysis is mostly in my head."

The Auckland medical officer of health, Dr Virginia Hope, says her office has provided "a very modest sum" to help with sampling over the past three to four years, and now to analyse the results to confirm what are the causative species and at what times during the year they are a problem.

"We would like to be able to provide better public information, and this analysis should give us the ability to warn the public as to the potential threat in given areas at given times of the year," Hope says.

She agrees that on balance of probabilities hydromedusae are the cause, but also points out that anemones are occasionally a problem; two years ago a bather was badly affected near Kawau Island by anemone stings which resulted in them suffering neurological problems.

While she recognises a need for further studies, Hope says looking at factors such as wind and ocean currents in relation to the outbreaks, and the origins of hydromedusae for that matter, is more an environmental issue than a public health one, and requires funding for environmental scientists to undertake the work.

"Auckland Healthcare is not a funder per se, nor do we employ environmental scientists, and from our perspective it is more useful to be able to say this is a problem and this is how you respond' than to delve further into cause and effect," Hope says, adding that their role in the problem to date has come from "stretching a discretionary budget", and she can not guarantee funding for any further sampling in the coming year.

Freudenthal's perspective is that funding for research is crucial.

"While we've honed in on the kind of organisms causing the problem we need to know a whole lot more about them if we're ever going to develop ways to control their numbers or combat their effects ... or know with accuracy when and where it's safe to swim."

The Freudenthals have returned to Long Island where their work is in high demand -- although both are now semi-retired -- but will be back at Leigh Marine Laboratory next summer, working to understand the eruption of this tiny but highly toxic and ubiquitous "stingy thingy" in the Gulf.

Bruce Bisset is the editor of Vision Hauraki.