Science & Environment

Warm weather sees boom in UK jellyfish blooms

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Media captionSwimmer Sean Conway is picking his way through large blooms of jellyfish en route to John O'Groats

Researchers say that the recent spell of warm weather has seen a rapid increase in jellyfish blooms around Britain's coasts.

The long, cold spring meant there were very few reports before June.

The Marine Conservation Society (MCS) now says several species including the Lion's Mane are being reported in rapidly growing numbers.

This particular species has a powerful sting and scientists are advising people not to touch them.

For the past ten years the MCS has carried out a national jellyfish survey based on reports from members of the public.

This year was extremely quiet until June, and scientists say that the reason was the poor winter weather.

"What seemed to happen was that we had the very cold spring," said Dr Peter Richardson, biodiversity programme manager with MCS.

"Normally we'd be receiving records from January onwards, this year we didn't have anything until May."

Bloom boom

The warm weather in July has led to an influx of information from all parts of the UK.

"We are getting anecdotal reports of people saying well 'I've been to this beach in the southwest for many years and I've never seen so many jellyfish' - we do tend to get that each year," said Dr Richardson.

Earlier this month the Foreign Office updated its travel advice for Greece in the wake of large jellyfish blooms there, but scientists stress that there are different factors and different species here in the UK.

Image caption Lion's mane jellyfish can stretch to over two metres and have a powerful sting

In Britain, Blue and Compass jellyfish are very common in the South West of England. The Moon species is being found all around UK coastal waters, in large numbers in some places.

There are also growing numbers of Lion's Mane around North Wales and the North West of England.

"They're our biggest jellyfish, they grow to about two metres wide and have metres of trailing tentacles, and they have very powerful stings, said Dr Richardson.

"They actually feed on the Moon jellyfish, so you tend to get big blooms of Moon and then Lion's Mane after."

Stinging seas

The scientists say the public should be very careful in the way they approach this species.

"We ask people to report what they see online and send us photos," said Dr Richardson.

Image caption Barrel jellyfish are usually found in the Irish sea but come further south as the waters warm

"But always look and don't touch, as they can sting and that could really spoil your day,"

There are competing views about why jellyfish blooms are increasing. There is some evidence that pollution is driving up the number of algal blooms and depriving the seas of oxygen.

In these environments, shellfish and other species struggle to survive. But jellyfish do well.

There are also concerns about overfishing. Researchers point to the collapse of the herring fishery in the Irish sea as helping to increase the numbers of jellies there.

"They are great opportunists, they have a unique design, if you take away their competition, they will take advantage of that situation." said Dr Richardson.

However some scientists say that the boom in blooms is down to a natural cycle that over the course of 20 years or so sees the rapid growth and die-off of jellyfish.

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