Swarms of Portugese man o' war 'jellyfish' lurk off coast of Nelson
Visitors to coastal areas of Nelson and Tasman Bay are being warned to watch for a regular summer nuisance, the Portugese man o' war.
Large numbers of the bluebottle jellyfish have been spotted in waters near D'urville Island over the weekend.
The Portugese man o' war is distinguishable by its float or bladder which looks like a little balloon and can be popped if stood on.
The main risk associated with the man o' war was its venomous tentacles that can deliver a painful - and sometimes fatal - sting, which manifests as red, whip-like welts on the skin.
Its lightweight composition meant it relied on wind and tidal currents to propel itself through the water.
Despite its appearance, the Portuguese man o' war is not a jellyfish but a siphonophore.
NIWA marine biologist Dr Dennis Gordon said it was not unusual for Portugese man o' war to congregate in this part of the country, although they were more likely to be seen on west coast beaches than on the east coast.
For the time being, strong southwesterly wind blowing through the region was keeping more blue-bottles from entering the bay or washing ashore.
However, with Metservice forecasting a northerly change on Wednesday the potential for the blue bottles to move closer to shore in the coming days would increase.
With school now finished for the year and warmer temperatures, beach goers to popular locations like Tahunanui and Kaiteriteri could soon be having to exercise caution in and out of the water to avoid being painfully stung.
Since the weekend, blue-bottles had also been seen at Tata Beach, Golden Bay, as well as further sightings at Mapua and Motueka.
Nelson man Jason Beattie noticed a number come ashore while staying at a bach at Tata Beach.
"I went for walk down the beach to see if the sea was alright to launch my boat. It wasn't so I walked down the shoreline with golden bay kayaks dogs that followed me .Thats when I noticed a continuous line of man o' wars along the waters edge," he said.
Gordon said it was also common to see large clusters of the creatures.
"It depends on many combinations of factors like the reproduction of the organism, the food and plankton, winds, tides and currents, water temperature, they all play a role so that in any one year its going to be a little from the year before or the year after."
Gordon said that while deaths caused by man o' wars were rare, quick treatment of any sting was necessary to reduce pain and discomfort.
"The thing that's most important is to flush any jellyfish sting with lots and lots of salt water," he said.
Medical assistance should be sought on more serious symptoms such as shock or cardiac distress.