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A warmer-than-usual summer is bringing an influx of microscopic jellyfish onto Auckland's eastern beaches, sparking a wave of reports of swimmers getting stung.
The Auckland Regional Public Health Service has received 26 reports of swimmers developing rashes from the stings, with more cases likely to have gone unreported.
Twenty cases have been from Takapuna beach, with Kohimarama and St Heliers reporting three each.
Swimmers are urged to also take care on other east coast beaches.
"What we've had is a very, very warm summer coupled with a La Nina which has meant that water temperatures have been around a degree warmer than normal. With the La Nina on east coast beaches, you get often an onshore breeze which actually brings the jellyfish into the shore," said public health doctor Dr Brad Novak.
The stings appear as little red bumps, often hundreds to thousands of them quite close together on the part of the skin covered by swimming garments. They can cause itching and redness, and some can be painful.
Children are more commonly affected than adults as their skin is softer. Dr Novak said the stings appear to take place once out of the water. The tiny animal gets into the swimsuit and then gets trapped in the fibres of the fabric once the swimmer steps out of the water.
"Then they dry out and that's when they sting."
The act of towelling down applies pressure that also makes the animals sting.
Dr Novak said the best thing to do was to remove the togs as soon as possible and shower, preferably with saltwater.
Little is known about the habits of these tiny jellyfish.
Until recently, the rash was thought to be caused by sea lice, but sea lice tend to bite on exposed areas of skin.
MICROSCOPIC STINGERS
Also known as hydromedusae, they are a cousin-species of jellyfish, with tiny tail-like projections which deliver a stinging toxin designed to immobilise their zooplankton prey.
Their stings cause what is known in medical circles as "sea-bather's eruption", a rash that is red, itchy and sometimes painful.
The only sure way to avoid being stung is to avoid swimming at the affected beaches. Alternatively, remove togs as soon as possible after getting out of the water and shower - especially the area covered by the togs. A saltwater shower is preferable.
If a rash develops, have a shower and get into cool clothing. Calamine lotion may help. Mild steroid creams like hydrocortisone or antihistamine tablets can help if the rash persists. See a doctor if it worsens.
Togs need to be laundered properly, as the jellyfish can still sting even when dead.
