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Barrel Jellyfish Sightings Surge Around UK and Ireland as Man O’ War Reports Plunge

The Marine Conservation Society attributes the shift to warming seas, based on citizen reports that require further study.

Overview

  • The Marine Conservation Society’s latest Wildlife Sightings Report logged 1,327 records across the UK and Ireland from October 1, 2024 to September 30, 2025, including 310 barrel jellyfish, up 230% year on year.
  • Moon jellyfish remained the most reported species with 316 sightings, alongside the highest share of large blooms since 2016.
  • Reports of the Portuguese man o’ war fell by more than 80% to 46, a drop the society links to fewer Atlantic storms pushing them ashore.
  • Turtle observations rose to 12 confirmed sightings, including nine leatherbacks with eight alive, mostly off the south‑west coast.
  • Scientists suggest warmer seas and shifting currents may be influencing these changes, while emphasizing the citizen‑science basis of the data and advising the public not to touch washed‑up specimens.