An unusually high number of jellyfish have arrived in UK seas this summer, experts have reported. Warm sea surface temperatures, exacerbated by global heating, have created favourable conditions for jellyfish blooms, which follow warm currents to the coast for their yearly reproduction cycle.
Record-high sea surface temperatures in April and May, according to the Met Office, are expected to lead to a greater number of blooms and a prolonged stay, as well as the potential arrival of new species that prefer warmer waters. The Marine Conservation Society recorded 1,432 jellyfish sightings in 2024, a 32% increase from the previous year.
Notable species include the barrel jellyfish, which can grow up to a metre in diameter and has a mild sting, and the compass jellyfish, identified by dark stripes and long tentacles that cause a painful sting. Other species spotted include moon, lion's mane, blue, and mauve stinger jellyfish.
Abigail McQuatters-Gollop, a marine conservation specialist at the University of Plymouth, noted that jellyfish are a foundational element of the aquatic food web and a food source for turtles. She said evidence suggests climate change and warmer waters are likely to increase jellyfish blooms.
Jellyfish have a short lifespan, with some born and dying within the same summer. After the season, they may follow currents back to sea or die from exhaustion of food supply, storms, or old age. Extreme weather, a consequence of climate breakdown, can also break apart their fragile bodies, which are composed of 90% water.
