GROWING numbers of jellyfish are lurking in UK waters, just as many people are heading for the beach during the holidays.
Swarms of the creatures have been seen in many coastal areas this year and even caused the shutdown of the Torness nuclear power station in East Lothian by clogging up a seawater inlet.
Experts are now urging people to monitor numbers of the species as part of a national survey aimed at explaining the increase in population.
The Marine Conservation Society (MCS) said it expects to find evidence of increasing numbers of particular types of jellyfish, including barrel, moon, compass, blue and lion's mane.
It says that some areas of the UK waters already resemble a "jellyfish soup" - including the Irish Sea where large numbers of moon, lion's mane, blue and compass jellyfish have already been reported. Other sightings have been made from North Somerset to the Firth of Clyde.
Last month, the Torness power station switched off both its reactors for two days after moon jellyfish, which are less than a foot in diameter, were discovered in the seas near the site where they clogged seawater filter screens.
Since 2003, more than 6,000 jellyfish encounters have been reported and the MCS said it hoped the survey would help improve understanding about where and when jellyfish occur around the UK.
Peter Richardson, biodiversity programme manager for the MCS, said: "The jellyfish survey is an excellent way for people to get involved in finding out more about our threatened seas.
"There is strong evidence jellyfish numbers are increasing around the world, including UK seas, and these increases have been linked to factors such as pollution, over-fishing and possibly climate change.
"We should consider jellyfish populations as important indicators of the state of our seas, and the MCS survey helps provide some of the information we need to understand more."
Mr Richardson added: "Since May we have also received reports of large numbers of several other species of jellyfish from round the UK - it is another good year for the jellyfish."
The survey data is being analysed with the University of Exeter. Early results show interesting differences in the distribution of the larger jellyfish species around Britain.
People who take part in the survey are also being warned not to touch the jellyfish, since many of them sting. Jellyfish are the staple diet of critically endangered leatherback turtles which are also seasonal visitors to UK seas.By comparing the distribution of jellyfish with environmental factors such as sea temperature, plankton levels and current flow, the MCS aims to understand what influences the distribution of leatherbacks, too.
This year there have been three confirmed leatherback sightings since June, all off the west coast, where jellyfish blooms have also been reported.
Jellyfish types which are being recorded include the barrel jellyfish, which grows to about 3ft across but is not a threat to people; the blue jellyfish, which grows up to 1ft in diameter, and has a sting akin to nettles; and the similar-sized compass jellyfish, which has a sting that causes weals to human flesh. The biggest UK jellyfish is the lion's mane which can be up to 7ft in diameter and has tentacles up to 120ft long. It's sting can cause serious injury. The moon jellyfish is often found in sea lochs, but is not a threat to human beings.