PUBLISHED: 12:34 08 July 2014 | UPDATED: 13:19 30 August 2017



Giant jellyfish seen off the coast of Cornwall

Giant 20 kilo jellyfish up to one metre in diameter have been making appearances in our waters, reports Matt Slater, Marine Awareness Officer with leading local wildlife charity Cornwall Wildlife Trust.

Matt along with his famous surfing dog Mango was lucky to have the opportunity to swim with an awesome barrel jellyfish in the Percuil Estuary near St Mawes.

Watch the video at . Mango helps to give some excellent perspective on the sheer size of this mesmerising creature!

Many people will have seen these alien looking creatures when on and in the water. This year has been an extremely good year for this species that has been described as the gentle giant of the jellyfish world! And many more jellyfish species have started turning up around our coasts, potentially bringing with them the world’s largest marine turtle!

“It was an otherworldly experience” said Matt Slater of his experience swimming with the giant barrel jellyfish,

“These creatures are incredibly beautiful when you get a close look at them. The tentacles really look like soft coral, and round the edge of the jellyfish’s umbrella like bell there is a deep blue line punctuated every twenty centimetres or so with a tiny dot, a sensory statocyst. Jellies are more aware of the watery world around them than you may imagine. They are constantly swimming up and down in the water column looking for profitable patches of plankton. The statocysts are their sensory cells that enable them to orientate and tell up from down.”

Like a basking shark, barrel jellies feed exclusively on plankton which is caught with sticky mucous covered tentacles, and like a basking shark they are fortunately totally harmless to humans, their stings being too weak to get through human skin.

'Lots of people have been calling Cornwall Wildlife Trust to ask us why there are so many jellies this year. In the spring tiny anemone like jellyfish polyps’ living on the sea bed expand in size and then bud off thousands of tiny larvae,' says Matt Slater. 'Most years these larvae will perish but in years where the conditions are good, temperatures are optimal, there is plenty of planktonic food and predators do not eat them all, large numbers of them will survive creating these huge jellyfish swarms. It is a boom and bust cycle. In fact according to our records the last time such large numbers of Barrel jellyfish were seen in Cornwall was in 2002.'

On Cornwall’s north coast huge numbers of blue jellyfish have been found. This week Matt and his fellow members of Holywell Bay Surf Club paddled through a swarm containing hundreds of these blue stingers, between Holywell and Perranporth. Unlike barrel jellies blue jellies can give a mild sting so please take care around them if you find any. Matt reported “We also saw compass jellies and moon jellies last night so jelly season is officially here!”

One of the most exciting things about this news is that where there are jellyfish there is a greater chance of seeing their predators. Two sightings of leatherback turtles have already come into Cornwall Wildlife Trust this summer, one off Porthcurno and one in Falmouth Bay. The leatherback turtle is a prehistoric looking creature, the largest marine turtle species, growing to up to eight foot long. It ventures north into Cornish waters in the summer months to feed on jellies!

We urge the public to get in touch and record their sightings of marine animals. This information is incredibly useful and appreciated. To submit a record please use our user friendly website

Cornwall Wildlife Trust work to protect Cornwall’s wildlife and wild places. There are many ways you can get involved visit for more information.

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