Holiday-makers are being called on to report their sightings of jellyfish at beaches across the UK, as part of a national survey.
As the school holidays begin, the Marine Conservation Society (MCS) is again urging people to take part in its annual jellyfish survey.
Large jellyfish blooms have already been reported washing up on beaches in England, Scotland, Wales, Northern Ireland and the Isle of Man, and as the UK's seas warm up during the summer, more jellyfish blooms are expected, the MCS said.
Peter Richardson, MCS biodiversity programme manager, said: "This year's jellyfish season started in earnest in April in the Irish Sea, when barrel and moon jellyfish were reported off the Welsh coast.
"Through May and June, barrel and moon jellyfish reports increased, with moon jellyfish reports coming from elsewhere, along with reports of other species such as the beautiful blue and compass jellyfishes.
"We started receiving reports of stranded lion's mane jellyfish off Wales and Northern Ireland in June. Lion's mane jellyfish and some other species can sting, so as ever, we are encouraging holidaymakers to take part in our national jellyfish survey, but the key message is look, don't touch!"
The survey aims to uncover the little-known habits of British jellyfish, as part of a wider programme to find out more about leatherback turtles that migrate thousands of miles to UK waters to feed on jellyfish each summer. By mapping where and when the jellyfish are seen, MCS hopes to understand more about leatherback turtles while they visit in UK seas.
Mr Richardson added: "The jellyfish survey is an excellent way for people to get involved in finding out more about our threatened seas.
"It appears that around the world jellyfish numbers are increasing, especially in our temperate seas, and scientists have linked these increases to factors such as pollution, over-fishing and possibly climate change.
"We should consider jellyfish populations as important indicators that show us what happens when we treat our seas badly, telling us that our marine resources are in desperate need of proper management."
MCS is interested in sightings of the six larger jellyfish and two jellyfish-like species likely to be encountered around the UK coast, which are known to be leatherback prey. More than 6,000 jellyfish encounters have been reported since the MCS Survey was launched in 2003.
The survey data will be fully analysed in collaboration with the University of Exeter.
To take part in the survey, download the MCS full-colour jellyfish photo-ID guide and recording form from www.mcsuk.org . Jellyfish encounters can also be reported in detail online.
The MCS is a charity dedicated to the protection of seas, shores and wildlife. It campaigns for clean seas and beaches, sustainable fisheries, protection of marine life and their habitats, and the sensitive use of marine resources for future generations