Holidaymakers and locals in north Wales are being asked to report jellyfish sightings as part of a major survey.
The lion's mane jellyfish has a nasty sting
Research is being carried out by the Marine Conservation Society following mass strandings of moon jellyfish in north Wales.
Experts are also hoping it will lead to a better understanding of the endangered leatherback turtle, which feeds on jellyfish.
The society has produced free jellyfish identification guides.
It is encouraging seaside visitors and people who use the sea regularly to record any jellyfish they encounter.
Species officer Peter Richardson said many sightings had already been received.
"We are urging anyone who is fishing, sailing or walking along beaches to
record their jellyfish encounters and join in this effort to understand the
ecology of our fabulous jellyfish," he said.
Reports so far suggest that the jellyfish are appearing in much the same
way as 2004, with millions of harmless moon jellyfish swarming along the west coasts of Wales, Scotland, and England.
In many areas, the moon jellyfish swarms are usually accompanied by the largest species in Britain, the lion's mane jellyfish, which has a powerful sting.
"While we welcome public participation in our survey,
the MCS message is `Look, don't touch', as some jellyfish, and especially the lion's mane, can give you a very painful sting," Mr Richardson said.
The C lamarkii, or blue jellyfish, has been recorded in Welsh waters
"Large swarms of lion's mane jellyfish have already appeared off western
Scotland, and in late June we received a report of a 1.5m wide, 5m-long specimen spotted off the Isle of Man."
Last year proved a particularly good one for jellyfish-spotters. "It is not clear why large numbers of some species suddenly appear in UK waters, but we expect environmental factors such as
weather patterns and sea temperatures to play a role," Mr Richardson explained.
"The Met Office has already predicted that this summer's temperatures may be above average, so it will be
interesting to see how the jellyfish respond."
Mr Richardson said nature-lovers in Wales had proved extremely helpful, with the mass sightings at the end of June in Wales fuelling curiosity.
"Somebody reported a sighting of moon jellyfish last weekend on Anglesey," he said.
In June around 1,000 moon jellyfish came ashore at Blackrock sands in Morfa Bychan, near Porthmadog.
The moon jellyfish, which are transparent with purple rings and are umbrella-shaped , were brought to shore by warm sea currents.
Anyone who wishes to help with the survey can download a guide and recording forms from the Marine Conservation Society website, or call the office to request a hard copy.