Why sightings of jellyfish and Portugese Man o’ war are rising on UK coasts

Climate change may be impacting jellyfish diversity in the UK, experts suggest

Portuguese man o' war have been increasingly washing up on the British coastline (Getty Images/iStockphoto)

Thunderstorms across the UK have resulted in an increase of jellyfish sightings along the British coast.

Reports of Portugese man o’war in UK waters have risen by two per cent, the Marine Conservation Society (MCS) said, while a total of 1,315 jellyfish were sighted this year.

Though they are commonly called jellyfish, the Portugese man o’war are in fact a species of siphonophore- a colony of single-celled organisms that are incapable of moving through the water on their own and so are typically ocean drifters.

They are also known as bluebottles thanks to their beguiling shades of purple and blue.

Despite their attractive appearance, Portugese man o’war are named so due to their piercing venom which can paralyse or kill small fish and crustaceans.

Though the sting can be very painful and cause welts on the skin for humans, it is rarely fatal.

As they prefer to drift in open waters, it is unusual for these creatures to be seen in the UK. They were mainly sighted along the southwest coast and the west coast of Scotland, according to the charity which added that “westerly winds” had carried them across the Atlantic.

Reports of portugese man o’war being spotted have risen by two per cent (Getty Images/iStockphoto)

A spokeswoman for the MCS said changes in temperatures may be affecting “jellyfish diversity” in the UK.

“Storms in October 2021 and February 2022 led to an increase in Portuguese man o’war sightings, which were up by two per cent from the previous year,” she said.

“Sometimes stranding at the same time was the violet sea snail, which floats on the surface in bubble rafts, feeding on Portuguese man o’wars.”

The MCS regularly records sightings of eight jellyfish species, with the compass jellyfish and the moon jellyfish, each accounting for 23 per cent of sightings, seen in smacks - the collective noun for jellyfish - of more than 100.

The spokeswoman said 11 other species were spotted and added: “The charity saw an increase in ‘other’ species reported, up from five per cent to nine per cent this year.

“Among these were the bioluminescent crystal jellyfish, which made up three per cent of total sightings, and sea gooseberries at one per cent - the highest percentages reported to date.

“Crystal jellyfish are usually found in the Pacific Ocean, rarely spotted in UK waters, suggesting that warmer temperatures may be impacting jellyfish diversity in the UK.

“Tracking reports of ‘other’ species like these could show how changes in temperatures might be impacting jellyfish diversity in the UK.”

Compass jelly fish washed up on the south coast Cornwall (Getty Images/iStockphoto)

A total of 11 turtles, which feed on jellyfish, were reported, six of which were live leatherback turtles spotted on the coast of Scotland.

Amy Pilsbury, MCS citizen science project lead, said: “We use these sightings, alongside scientists, to spot trends in the distribution of jellyfish and marine turtles around the UK.

“Investigating the relationships between species can help us to discover more about our amazing underwater world and how it might be changing in response to things like climate change.”