Free diver and conservationist Iestyn Morgan has filmed what he described as a giant lion’s mane jellyfish near Trefin Beach on the Pembrokeshire coast. He said it was the first example of the species he had seen in Wales and that he “couldn’t believe” its size.
Morgan estimated the jellyfish’s body was about 10 to 15 metres long, describing it as comparable to a bus or a small train. He said he first saw several tentacles in the water, with the number appearing to increase from three to 10 and then 20. The tentacles eventually extended beyond what he could see.
The Wildlife Trusts says lion’s mane jellyfish are named for their long, flowing tentacles. The animals can grow up to 3 metres in length, while their tentacles can exceed 30 metres, making them among the longest animals on Earth. Morgan initially thought he had seen a compass jellyfish, which is native to UK waters, before recognising the animal’s unusual size.
Marine biologist Dr Cathy Lucas, of the University of Southampton, said the video showed the jellyfish’s “incredible length”. She told the BBC that the tentacles were so long and fine that swimmers might not see them, and recalled encountering detached tentacles during fieldwork in Scotland. She said they could continue to sting after breaking off.
Lucas described the sting as “nasty” and the worst among jellyfish found in the UK, but said it was not dangerous. Her advice was not to touch lion’s mane jellyfish; if a piece of tentacle lands on the skin, she recommended flicking it away with a stick and washing the area in warm water.
The species is more commonly found in colder waters off Scotland, although Lucas said public sightings indicated that lion’s mane jellyfish occasionally reach the Welsh coast later in summer or in autumn. Morgan said he had noticed more jellyfish and other warm-water species in Welsh waters while filming, including a triggerfish, and said his footage aimed to make marine life more accessible while raising awareness of threats facing the seas.