Giant barrel jellyfish, known for their large size and frilly mouths, have been increasingly spotted along British coastlines, with sightings surging by 230% compared to last year, according to the Marine Conservation Society's annual wildlife report.
The species rose to become the second most reported jellyfish in UK waters, up from fifth place in 2024. Anna Bunney, citizen science programme manager at the society, said the increase may be linked to warmer sea temperatures and changing ocean currents, though more data is needed to understand the fluctuations.
Moon jellyfish remained the most sighted species for the second consecutive year, with 316 recorded, making up 24% of all 1,327 jellyfish sightings. Blooms of over 100 moon jellyfish increased by 68% from last year, the highest proportion since 2016/17.
Mauve stinger jellyfish also saw a record increase, with sightings up 31% from 2024. In contrast, Portuguese man o' war sightings fell by 83%, likely due to fewer storms this year—six compared to 12 last year—reducing the number washed ashore.
Geographically, over half of sightings occurred in England. Moon jellyfish were most common in England, while barrel jellyfish topped the list in Wales and Scotland. Mauve stingers were largely found along the south-west coasts of England and Wales.
Overall, total jellyfish sightings across the UK and Ireland fell by 6% between October 2024 and September 2025 compared to the previous year.
