BEACH-GOERS and watersport enthusiasts have been warned to avoid poisonous compass jellyfish being seen in the waters off South Devon.

Members of the public have contacted the Herald Express to report sightings of the jellyfish, which are often about eight inches in diameter and have tentacles of 24 inches.

This picture was taken in Torquay harbour.

The jellyfish are known to have a powerful sting, and can be harmful even when washed up on the beach.

The compass jellyfish has a bell-shaped body with 16 brown markings which give it its name.

Its background colour is cream to yellowish-brown, although many other colours have been observed.

Four long tentacles — or oral arms — hang under the centre of the bell, where the mouth of the jellyfish is located.

In most cases, 24 thinner extensile tentacles hang from the bell's rim.

Don Proctor, who lives in Torquay, took these photographs while walking around the harbourside.

He said: "I was just strolling along, looking at the divers repairing Haldon Pier, and I noticed the jellyfish.

"They were different from any I'd seen before. There markings were very striking. There were about four or five of them. I wondered if they were dangerous."

Dr Dave Gibson, at Plymouth's National Marine Aquarium, said: "Thanks to warm ocean currents and naturally high levels of nutrients, the coastal waters of the UK has a high diversity of jellyfish.

"At this time of year we are seeing plankton blooms close to shore as sea temperatures rise. This is the perfect environment for jellyfish to thrive.

"In most cases jellyfish don't pose a threat to humans, but the Compass Jellyfish does have a potent sting and therefore should be avoided.

"The tentacles can still sting even after the jellyfish is washed up on the beach, so don't allow children or pets to touch them if they find one washed up.

"In the case of Torquay Harbour, the aggregations of jellyfish will move on as the plankton blooms migrate along the shoreline with tide and current.

"In recent years, commercial fishing has reduced fish numbers in UK waters to only 10 per cent of what they were only 100 years ago.

"If we don't address the issues facing our fish stocks now, the UK will see more cases of jellyfish swarms in the future and the latest news will seem trivial by comparison."

A full-colour jellyfish photo-ID guide and recording forms can be downloaded from the Marine Conservation Society website, www.mcsuk.org