Page last updated at 06:22 GMT, Tuesday, 2 June 2009 07:22 UK

Giant jellyfish tagging under way

jellyfish Rhizostoma octopus
A fieldworker tags a jellyfish Rhizostoma octopus in Carmarthen Bay

Marine biologists are tagging jellyfish off the coast of Wales in a bid to discover more about their life.

More than 30 barrel jellyfish, some the size of dustbin lids, will be tagged in Carmarthen Bay this week as part of a joint Welsh and Irish project.

When the jellyfish eventually die, the tags, waterproof minicomputers, will wash ashore with their individual data.

Dr Victoria Hobson of Swansea University said: "We don't even know how long these jellyfish live."

The project, called EcoJel, was launched last year as a collaboration between Swansea University and University College Cork.

It aims to assess the opportunities and detrimental impacts of jellyfish in the Irish Sea.

Researchers from three universities, Swansea, Cork and Queen's University Belfast, will target four sites - Rosslare and Dublin on the Irish coast and Carmarthen and Tremadog Bays in Wales.

It's fairly unusual to find a creature so universally recognisable whose life history is unknown
Dr Victoria Hobson, Swansea University

Although consisting of 98% water and some being the size of dustbin lids, biologists said barrel jellyfish (Rhizostoma octopus) are "tough, robust animals", making tagging possible.

Dr Hobson said: "Over the next few days we'll be going out on a boat in Carmarthen Bay, heading towards Saundersfoot and Tenby, not far out from the beach.

"Myself and a couple of colleagues will go over the side, snorkel up to the jellyfish and tie small tags - about half the size of your little finger - around the trunk of the jellyfish with a cable-tie.

A recent aerial photo of barrel jellyfish taken by the research team

"They'll be quite loose but won't be able to slip off either end. Then we'll just leave them."

Dr Hobson explained: "When each jellyfish dies its tags floats to the surface or gets washed up on the shore. If someone finds one we'll pay them £25 to return it to us."

'Currents and tides'

The team affixed 11 tags in the area last year and have so far had six tags returned.

One of the key facts that the team is trying to ascertain is whether the jellyfish consciously try to stay in the Bay or whether they succumb to currents and tides.

"We don't even know how long these jellyfish live," said Dr Hobson. "It's fairly unusual to find a creature so universally recognisable whose life history is unknown, rather than some unknown micro-organism.

"The project is four years long but already we are learning about these jellyfish.

"We did an aerial survey in February and saw six of them in coastal waters then. Just the fact that they were there then was new to us."

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