“Over the last few weeks, divers and boats in the Falmouth area have been encountering more and more Barrel Jellyfish [Rhizostoma Octopus, Rhizostoma Pulmo],” says Mark Milburn of Atlantic Scuba, near Penryn.

“These large pelagic species can reach up to 90cm across, the sort of size that has been encountered.”

The creatures feed mostly on plankton and, says Milburn, “are thought to spend most of the time at depth, coming up when the plankton blooms”.

“With the increasing water visibility, as the plankton starts to die back, they are getting easier to spot,” he says.

Although a large jellyfish, the Barrel Jellyfishs sting “isnt strong enough to be harmful to humans”.

For marine biological enthusiasts, Milburn adds: “If you manage to see one and get close, look for the various creatures that live within the jellyfish.