Over the past year, the UK has witnessed a remarkable increase in jellyfish sightings along its coastlines and beaches. According to a recent survey conducted by the Marine Conservation Society, the number of jellyfish spotted in UK waters has surged by a staggering 32%. While the iconic barrel jellyfish remains a common sight, rarer warm-water crystal jellyfish have also made appearances. What’s causing this surge in jellyfish populations, and what does it mean for the UK’s marine ecosystem?

Jellyfish populations naturally fluctuate over time, but climate change appears to be playing a significant role in creating favourable conditions for their proliferation. One key contributor to this phenomenon was a marine heatwave in June, which led to an increase in UK water temperatures by approximately 3-4°C. This warming trend aligns with the broader global picture of rising temperatures. The world has warmed by 1.1°C compared to the pre-industrial era, largely due to human activities like burning fossil fuels. This year, a series of record-breaking events, including the highest global average ocean temperature in August, have set off alarm bells among scientists.

The Marine Conservation Society’s annual wildlife-sightings report relies on data from the public, collected through an online form or app. Over the year from October 2022 to September 2023, jellyfish sightings increased significantly, with most observations concentrated on the west coasts of the UK, particularly in Cornwall and Wales. Astonishingly, 11% of sightings reported large blooms of over 100 jellyfish.

The iconic barrel jellyfish, colloquially known as the “dustbin-lid” jellyfish, can grow to over 3 feet in diameter, characterised by its eight thick, frilled arms. There were 467 sightings of these magnificent creatures. Additionally, other jellyfish species like the Lion’s mane, Portuguese Man o’ War, Moon and Compass Jellyfish were also spotted.

While the sting of a barrel jellyfish is typically not harmful to humans, it’s best to avoid touching them. It’s important to note that jellyfish populations are subject to natural boom-and-bust cycles that may span over two decades. However, the current survey provides a valuable insight into the influence of climate change on marine ecosystems.

Experts emphasise the need for more research to determine whether this year’s high jellyfish numbers are part of a long-term trend or linked to the marine heatwaves. The potential implications of rising sea temperatures extend beyond jellyfish, as warmer UK seas are expected to alter fish stocks by affecting the availability of food for species like cod.

The Marine Conservation Society’s survey also documented 12 turtle sightings, including the magnificent leatherback sea turtle, the largest of its kind. The surge in jellyfish and other marine species sightings is a stark reminder of the profound impact climate change is having on our oceans. The time for action in addressing climate change and protecting our marine ecosystems is now. We must continue to monitor these trends and invest in research to better understand and mitigate the consequences of warming waters on our environment.