SWIMMERS in the sea off Felixstowe are today urged to watch out for an invasion of jellyfish this summer with huge numbers reported around the coast.Stranded and dead ones have already been found at Landguard, and a number have swum upriver and been spotted in the dock at Ipswich.

SWIMMERS in the sea off Felixstowe are today urged to watch out for an invasion of jellyfish this summer with huge numbers reported around the coast.

Stranded and dead ones have already been found at Landguard, and a number have swum upriver and been spotted in the dock at Ipswich.

Marine environmental experts have also seen shoals of the fluorescent voracious predators sea gooseberries off Felixstowe - though not dangerous, some species can grow to the size of a rugby ball and be quite spectacular.

Most jellyfish are harmless but swimmers are being warned to exercise caution and not to touch them or swim near them.

The Marine Conservation Society (MCS), which wants holidaymakers to report jellyfish encounters, said there are potentially dangerous species and swarms of the hazardous Lion's Mane jellyfish have been seen this summer.

Landguard nature reserve ranger Malte Iden said people taking part in courses on the marine environment over the past two weekends had found jellyfish washed ashore.

"We were beach combing and looking in the tide pools and there were a number of jellyfish stranded on the shore," he said.

"It is hard to say whether there are large shoals out in the sea but if some have already been seen at Ipswich that would be a good indication."

The beachcombers also found sea gooseberries, also known as sea walnuts, Venus's Girdle and comb jellies because of their tentacles, though these were small in size.

Marine expert Teresa Naylor said most of those at Felixstowe and in the River Orwell were likely to be Moon and common jellyfish, which were harmless. Swarms were common because the creatures drifted together in the currents.

The MCS has had more than 300 reports of jellyfish around the UK this year.

Species policy officer Peter Richardson said: "Our jellyfish survey is revealing fascinating insights into the lives of these beautiful and enigmatic animals.

"Jellyfish will not purposely attack people, instead they catch fish and other marine creatures by spreading their tentacles like fishing lines.

"The tentacles of some species can inflict very painful stings to exposed skin, especially those of the Lion's Mane jellyfish, which can be a dangerous surprise to unsuspecting bathers.

"The other species most commonly found in UK waters are either harmless or inflict mild stings, but you never know how an individual will react to the venom.

"So we always urge caution and suggest that people use the MCS ID Guide and never touch or knowingly swim with jellyfish."

Jellyfish are the favourite food of the critically endangered leatherback turtles which visit the UK seas to feed on them.

In the last few weeks, vast blooms of the harmless Moon jellyfish have been reported, smaller numbers of the beautiful Blue and Compass jellyfish, and thousands of massive Barrel jellyfish.