Tiny jellyfish species normally found in the Yangtze basin in China sighted in British canal

This article is more than 2 years old

This article is more than 2 years old

First came the wasps, exotic sharks and marauding seagulls. Now the long hot summer has revealed another initially alarm-inducing animal in British waters – or more precisely, in the Middlewich branch of the Shropshire Union Canal.

Freshwater jellyfish normally native to the Yangtze basin in China have been spotted swimming in the waters near Bridge 23 of the canal between Middlewich and Winsford, according to the Canal & River Trust.

The jellyfish, Craspedacusta sowerbii, is transparent, the size of a 10p coin, and completely harmless to humans. It is a rare sighting but periodically turns up in waterways, including some of the charity’s 2,000 miles of canals, when water temperatures exceed 20C.

Sara Hill, an ecologist at the trust, said: “It’s a really unusual sight. We’re used to seeing all sorts of fish, birds and insects here in Middlewich, but jellyfish are a first and certainly make an interesting addition to the local wildlife.

“It’s thought that the hot and sunny weather could have encouraged the jellyfish to these parts and created perfect conditions for them, but we don’t know whether they will make their permanent home here so we’re finding out as much as we can.”

The jellyfish prefer standing water and feed on tiny organisms which they catch with their stinging tentacles, but are so small that they do not pose any danger to people.

The hot weather warming the canal waters may have encouraged the species at a particular stage of its lifecycle.

Facebook Twitter Pinterest Freshwater jellyfish in a Hungarian lake south of Budapest. Photograph: Janos Bugany/EPA

The species was first discovered by William Sowerby, the director of the Royal Botanic Gardens in Regent’s Park, in the garden’s tropical water lily tank in 1880. Plant-hunters had inadvertently brought the jellyfish to Britain during the Victorian era.

In 1928 the jellyfish were found in the unheated waters of Exeter Ship Canal and summer sightings have increased since the 1980s in canals, shallow freshwater lakes and flooded quarries.

The main “blooms” appear in August and September, usually when water temperatures exceed 20C. In previous years, the species has vanished again by October.

Gemma Rathbone, spokesperson for the Canal & River Trust, said: “It’s now pretty grey and drizzly up here so whether that will put them off, we don’t know.”

Freshwater jellyfish have spread to every continent from their natural home in the Yangtze basin in China. They are believed to have arrived in Britain in the 19th century when explorers brought back exotic flora and fauna from their travels around the world.

A different species of jellyfish has also been found in the waters of Liverpool’s South Docks, which is also managed by the trust. They enter from the adjoining River Mersey and have been spotted along the Leeds & Liverpool Canal.

Earlier this summer, thousands of moon jellyfish were spotted off the Welsh coast, with hundreds then washing onto beaches near Liverpool.