Expect more giant jellyfish as our waters get warmer

MONSTER jellyfish are likely to wash up on Welsh beaches in growing numbers in the coming years, a marine expert has warned.

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With the UK currently in the grip of a marine heatwave, warmer waters will bring larger and more dangerous - sea creatures closer to coastlines.

This summer, social media has been awash with photos of jumbo jellyfish on Gwynedd's west-coast beaches. In recent weeks, giants have also begun washing up on the Welsh coast in Conwy. A few have been reported on Rhyl beach, Denbighshire.

On Monday, Manchester visitor Lisa Whittaker came across several on Rhos-on-Sea beach. Valiantly she tried to slide one back into the water, but gave up after realising it was probably dead already.

Stranded jellyfish are 95% water and rapidly dehydrate when exposed to wind and sun.

“Never in my life have I seen one like it - and probably never again,” she marvelled.

“Impressively enormous” jellyfish have also been reported on Colwyn Bay beach. Local woman Dawn Roberts was left “shocked” by one, saying: “Never seen one so big in my life!”

All were barrel jellyfish, a British native that are the giants of the jellyfish world.

Strandings are not uncommon on Welsh beaches but, anecdotally, people are reporting ever-bigger specimens.

Certainly, feeding conditions this year have been ideal. UK waters are currently experiencing their second major heatwave of 2025, with sea surface temperatures currently well above average in the Celtic Sea, English Channel and southern North Sea.

Anomalies of 1.5°C-3°C above the 1982-2012 average have been registered, with readings of 17°C-20°C recorded in the English Channel. These sea temperatures are more typical of early August in the late 20th century, said the Met Office.