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