Jellyfish invasion: Britain to fight them on the beaches

  • @mjpmccarthy

The growing threat from swarms of jellyfish around Britain's coast is to be investigated for the first time by British and Irish scientists. Using the latest technology, researchers are planning to tag jellyfish to explore their life cycles and movement in a project known as Ecojel.

Jellyfish, which are one of the least studied forms of marine life, are having an increasingly harmful effect on tourism, aquaculture and fisheries as their numbers rapidly expand. Episodes of mass stinging of swimmers in the Mediterranean and large-scale damage to fisheries from the Black Sea to the South Atlantic have prompted the joint study from the universities of Swansea and Cork.

They are hoping to test the theory that overfishing maybe partly responsible for the rise in jellyfish numbers. Jellyfish and juvenile fish feed on the same plankton resources and if one is reduced the other expands.

Last November a jellyfish invasion wiped out Northern Ireland's only salmon farm, killing more than 100,000 fish. Millions of small jellyfish, known as mauve stingers, flooded into the cages about a mile into the Irish Sea, off Glenarm Bay and Cushendun.

The jellyfish covered an area of up to 10 square miles, with a depth of 35 feet, and although rescuers tried to reach the cages, the density of fish made it impossible. The fish farm's managing director, John Russell, said that he had never seen anything like it in 30 years in the business. "The sea was red with these jellyfish and there was nothing we could do about it, absolutely nothing," he said. Earlier in the summer, beachgoers in Cornwall and Dorset were warned to look out for the highly poisonous Portuguese man-of-war jellyfish.

Professor Graeme Hays, the head of Environmental and Molecular Biosciences at Swansea University, is leading the project. He is an expert on sea turtles, which hunt jellyfish as their principal prey. "There is actually very little known about jellyfish despite the fact that jellyfish blooms may be increasing because of overfishing and climate change, which could have huge socio-economic impacts," he said.

Overfishing in particular allowed jellyfish to get a hold in an ecosystem and take it over, he said. This had been seen off the coast of Namibia and in the Black Sea, where fisheries had collapsed as jellyfish became more numerous than the fish themselves.

"This is a serious threat," Professor Hays said. "In 20 years' time we may be looking at jellyfish and chips, rather than fish and chips." The threat to swimmers was also growing. The stings of some species of jellyfish found in British waters, such as those of the lion's mane jellyfish, were capable of causing death. The project would allow a broad-scale assessment of the role of jellyfish in the Irish Sea ecosystem, he added.

Professor Hays and his Irish counterpart, Professor Tom Doyle, will attach data loggers – small devices which record information such as water temperature and depth – to the biggest species that is found in British waters, the barrel jellyfish, which can measure three feet across.

Once the animals die, it is hoped that the data loggers will be washed ashore and found by members of the public. Tests have shown that the idea is workable in practice.

The scientists hope that they may be able to work out management strategies for fish farms to avoid jellyfish problems, but they will look as well at the possibility of harvesting some jellyfish species as food. This is increasingly happening in Asia. They will also be assembling all the information necessary to treat incidents of stinging from different species.

Eight dangers lurking around our shores

*Barrel or rootmouth jellyfish

Rhizostoma octopus
The biggest jellyfish commonly found in British waters, up to a metre in diameter. Robust, with a spherical, solid, rubbery and largely white bell, fringed with purple. The bell lacks tentacles but eight thick, frilled arms hang down from the manubrium (the mouth and arms, underside and centre of bell). Harmless.

*Blue jellyfish

Cyanea lamarckii
Up to 30cm. Similar shape to the lion's mane, but smaller with a blue bell through which radial lines can be seen. Mild sting.

*Moon jellyfish

Aurelia aurita
Up to 40cm in diameter. Transparent, umbrella-shaped bell edged with short, hair-like tentacles. Recognised by the four distinct pale purple gonad rings in the bell. Manubrium bears four short, frilled arms. Mild sting.

*Compass jellyfish

Chrysaora hysoscella
Typically up to 30cm. Colour variable, but usually has pale umbrella-shaped bell with diagnostic brownish V-shaped markings, 32 marginal lobes and 24 long, thin tentacles. Four thick, frilled arms hang from the manubrium. Mild sting.

*Mauve stinger

Pelagia noctiluca
Up to 10cm. Has a deep bell with pink or mauve warts, 16 marginal lobes and eight marginal, hair-like tentacles. Manubrium bears four longer frilled arms with tiny pink spots. More serious sting.

*Lion's mane jellyfish

Cyanea capillata
Large, usually 50cm but can reach two metres in diameter. Large, reddish brown, umbrella-shaped bell with mass of long, thin hair-like tentacles as well as four short, thick, frilled and folded arms. Very virulent sting, capable of causing cardiac arrest.


Velella velella
Not a true jellyfish, but a floating hydranth. Up to 10cm long and blue-purple in colour. Upright sail and chitinous float are diagnostic, with a mass of small tentacles surrounding the mouth on the underside. Found in swarms. Harmless to humans.

*Portuguese Man-of-War

Physalia physalia
Not a true jellyfish, but a floating colony of hydrozoans. Oval-shaped, transparent float with crest. Blue-purple, with many hanging fishing polyps below that may be tens of metres long. Extremely dangerous. Rare in the UK but if found in numbers they should be reported.