Dangerous jellyfish species spotted off Welsh beaches

More than 300 mauve stingers, or palagia noctiluca, were spotted off an Anglesey beach last week

A type of jellyfish plaguing beaches and bathers in the Mediterranean has been spotted off the Welsh coast.

More than 300 mauve stingers, or palagia noctiluca, were recorded off an Anglesey beach last week, as well as other locations as far south as Pembrokeshire.

The delicate, purplish jellyfish, whose bells grow to maximum of 4.7 inches (12cm), can cause a "very painful sting", one researcher said.

The Marine Conservation Society said the appearance of a warm water species in the UK is "not surprising" as sea temperatures here rise.

"It's a huge problem in the Mediterranean," said Christos Taklis, from Merman Conservation, which runs a citizen science project recording mauve stinger sightings in Wales.

Their sting contains neurotoxins that make it one of the Mediterranean's most dangerous, he added, affecting tourism and fishing.

The latest UK jellyfish data indicates mauve stingers made up just 2.6% of 1,432 sightings recorded by the the Marine Conservation Society last year.

Multiple blooms were recorded in the week up to 21 September, with aggregations of more than 100 in Pembrokeshire, Gwynedd and Anglesey.

More than 300 mauve stingers were reported at Trearddur Bay near Holyhead on 18 September.

"They can cause a very painful sting," Taklis said, explaining that if left untreated people can suffer heart problems or allergic reactions.

A mauve stinger seen in Trearddur Bay off Anglesey

"If you get stung, be calm and immediately leave the water."

The affected area can first be cleaned with sea water and baking powder to reduce "the extent of the poison".

Taklis said the stings can then be treated with hydrocortisone cream.

"We want to inform the public what is happening and to be careful."

The Marine Conservation Society's Calum Duncan said a UK-wide monitoring programme started a decade ago suggests jellyfish numbers are rising.

A bloom of mauve stinger jellyfish off west Cornwall and the Isles of Scilly affected a swimming competition in 2024

Jellyfish blooms - growths in population of species - depend on a number of factors, including nutrient levels, water temperature, storms and even fertiliser run off from farms.

"The warm summer and marine heat waves could be boosting natural processes," Mr Duncan said.

"We know these events can happen.

"We have heard of jellyfish blooms affecting fish farms in the west of Ireland so it's not surprising to hear these reports from Wales."

He encouraged people to report what they see and check ahead with lifeguards or conservation officers about possible jellyfish blooms before heading into the water.