Warmer weather brings increased numbers of jellyfish to our shores

The UK’s leading marine charity says people visiting the beach this summer should keep their eyes peeled for wobbly visitors who act as a barometer of the seas. After a slow start this year, jellyfish blooms started increasing in June and July as our coastal waters warmed up.

Every summer hundreds of reports of jellyfish sightings are made to the Marine Conservation Society’s (MCS) National Jellyfish Survey, which is in its 10th year. During the last decade, 7,500 jellyfish reports have been made by the public to MCS. The survey is providing valuable information about where and when jellyfish occur in UK seas amid global reports of a rise in jellyfish numbers.

Dr Peter Richardson is the charity’s Biodiversity Programme Manager and jellyfish expert: “There is some evidence that jellyfish numbers are increasing in places around the world, including UK seas, although some scientists argue that jellyfish numbers increase and then decrease normally every 20 years or so.

"However, others believe these increases are linked to factors such as pollution, over-fishing and possibly climate change. I think we should consider jellyfish populations as important indicators of the state of our seas, and the MCS jellyfish survey helps provide some of the information we need to understand more about them.”

This year was a relatively quiet one for jellyfish reports until the warm weather kicked in. “The scarcity of jellyfish reports before June was unusual and could well be linked to the exceptionally cold spring,” says Dr Richardson.

“However, as our waters warmed, sightings of jellyfish increased, with moon jellyfish reported in large numbers around the UK, reports of compass and blue jellyfish in the south west, and blooms of Lion’s Mane jellies around North Wales and North West England.”

Lion’s mane jellyfish have a powerful sting, and MCS urges anyone taking part in the survey and reporting their jellyfish encounters to “look but don’t touch!”

In early June, millions of jellyfish invaded thousands of miles of Mediterranean coastline, which scientists said threatened the health of the seas as well as that of the tens of thousands of tourists who head to the area annually.

“We still know relatively little about jellyfish, but large increases in numbers like those in the Mediterranean are telling us about the health of our seas and cannot be ignored,” said Dr Richardson. “As always we want people to let us know when they spot jellyfish either in the sea or on the beach.

"Sightings can be easily reported at www.mcsuk.org”.