Jellyfish swarm Westshore beach near Napier

Lion mane jellyfish washed up on Westshore Beach earlier this week. Photo / Supplied

As spring blooms, so do jellyfish and a fair few are blossoming on to the shores of Westshore Beach in Napier.

According to Niwa marine biology technician Diana MacPherson it's common to see blooms of jellyfish as the water temperature gets warmer, because it means there's no shortage of food for them.

A large number of jellyfish swarmed in for Guy Fawkes earlier this week.

They were probably more interested in feasting on the animal plankton feeding in shallow waters than watching fireworks, MacPherson said.

"Some jellyfish at or near the sea surface are at the mercy of strong wind and currents that can gather them into a dense group and direct them to beaches, bays or harbours where they become stranded, so it is normal for them to wash up."

Macpherson said the large flying-saucer shaped creatures photographed at Westshore were lion's mane jellyfish, or Cyanea rosea.

"It's the largest jellyfish species found all around New Zealand. Their bells are usually less than 50cm in diameter but can get up to 2m in diameter, she said.

She had a warning for beachgoers wanting to touch them.

"This one does sting through their tentacles, even after being stranded on shore. For some people stings may result in an allergic reaction.

"If stung, vigorously flush the stung area with lots of seawater (NOT fresh water) to rinse away the tentacles and stinging cells

"Pluck off any clinging tentacles with tweezers. Scraping them off or rubbing with sand triggers any active stinging cells to release more venom, so take care when removing tentacles and apply heat."

Although not popular with swimmers, MacPherson said jellyfish played an important role in marine food webs — as predators, or prey or as decomposing scraps of food for suspension feeders in the water or on the seafloor.