NIWA says long, hot days can mean more jellyfish are in the sea off New Zealand's beaches and warns people to be careful not to get stung.
There are around 35 species of jellyfish in New Zealand waters with the moon, lion's mane and spotted jellyfish being the most common.
Moon jellyfish (Aurelia sp.) have a bell-shaped whitish body, about 25-40cm across, and have a fringe of short tentacles around the margin of the bell. Lion’s mane (Cyanea rosea) is New Zealand’s biggest species of jellyfish, growing up to an impressive two and a half metres in diameter and with tentacles of up to 36 metres in length. Spotted jellyfish (Desmonema gaudichaudi) are dome-shaped with reddish-brown polka dots on the body.
At this time of year they stay close to the surface to chase food and can become stranded on the beach.
"As soon as the days start to get longer and there's more daylight, you get a bloom of more plankton. When there is more plant plankton, there's more animal plankton, which means you get more shrimps and things - and jellyfish feed on those small crustaceans," NIWA emeritus researcher and jellyfish expert Dr Dennis Gordon said.
Large numbers of bluebottle jellyfish were reported at Auckland's west coast beaches recently, more commonly known as Portuguese man o war they are steered towards the shore because they are light and have a gas-filled float, Gordon said.
Dr Gordon warns people to take care if they come across jellyfish this summer.
"Despite being really beautiful, the lion's mane and spotted jellyfish can produce a very painful sting, as can the bluebottle.
"Those who do plan on getting in the water should be cautious and wear a wetsuit if it is known that there may be jellyfish in the area."
Gordon said most jellyfish stings in New Zealand are not serious and victims should first flush the sting area with seawater. He said using urine to relieve the sting is a misconception.
"Jellyfish are enchanting, delicate creatures that should be appreciated, just not too close," Dr Gordon said.
