Bathers play part in tailing ‘jellies’

A MAP on the EcoJel website shows locations at which people were stung by jellyfish this year.

Report A Sting is an initiative of University College Cork and Swansea University.

Bathers are asked to document encounters with jellyfish. It’s part of a wide-ranging research effort in which EcoJel scientists carry out surveys from the decks of Irish Ferries ships and divers fit tags to the tentacles of lion’s main jellyfish — not a job for the fainthearted. The movements of the tagged jellies are tracked underwater. Reports from bathers are a valuable source of additional information.

Jellyfish are among the world’s most successful creatures; they first appeared over 500 million years ago and have remained largely unchanged ever since. The name is misleading; these are not fish, nor are they remotely related to bony animals. The American name, ‘sea-jelly’, is much more appropriate.

Like their after-dinner namesake, sea-jellies are 95% water. Their motto might also be an American one; ‘Keep it simple, Stupid!’: have a minimalist approach to life! Jellies have no skeletons, no respiratory systems and no brains. Oxygen diffuses through their skin and the nervous system is distributed, net-like, throughout the body rather than ‘urbanised’ at a central location. By contracting and pulsating its ‘saucer’, a sea-jelly can move around its immediate area but more extensive movements depend on ocean currents. Although a jelly has no eyes and can’t see, it has enough light sensitivity to tell which way is up and which is down.

There is one exception to the simplicity rule; the notorious jellyfish stinger is, according to Richard Dawkins, ‘probably the most complicated piece of apparatus inside any cell anywhere in the plant or animal kingdoms’. Millions of little harpoons are coiled under pressure waiting to be fired at the touch of, literally, a hair trigger. The torpedoes will kill any little creatures unlucky enough to blunder into one of the long, virtually invisible, tentacles. Victims are then absorbed directly into a primitive gut. The sting doubles as a defensive weapon; jellyfish have many enemies, including the giant leatherback turtle which is turning up increasingly in Irish waters.

The sting map shows high concentrations of incidents in the Irish Sea, particularly along the Welsh coast. Beaches in the Dublin area have been closed to bathers occasionally but Irish waters are much safer than those further south. Over 400 people were stung at a beach near Malaga on a single day. Dr Tom Doyle of UCC, told the Mooney Show recently that the Irish Sea has abundant populations of sea-jellies. The lion’s mane jellyfish, a large reddish-brown medusa with invisible tentacles up to 5m long, is particularly common. Most jellyfish stings are no more potent than those of nettles but the lion’s mane can induce very severe pain lasting five to six hours. Bathers were hospitalised following stings at Dublin’s Forty-foot bathing place in 2005. Lion’s manes invaded the area that year.

Nor is stinging the jellyfish’s only offence. Thousands of farmed salmon died when jellies entered their tank in 2007 and the cooling water intake of a Scottish nuclear power station was blocked by hordes of ‘moon’ jellyfish. The ‘moon’ is the familiar one you see washed up on beaches just about everywhere. It’s easily recognised by the four purple circles on the transparent ‘saucer’.!

One type of sea-jelly may be commercially exploitable; the huge ‘barrel’ jellyfish weighs up to 35kg, almost half the weight of an average-sized person. It is conspicuous enough to be seen from the air and EcoJel have carried out aerial surveys of it. The Irish Sea supports large numbers of barrels. It might just be possible to harvest these giants and export them to the Far East, where jellies are considered a delicacy.

Jellyfish populations seem to be increasing. Over-fishing may be a factor in this; many of their fish enemies have been so reduced in number that jellies are thriving. Rising sea temperatures, due to global warming, and nutrients carried into the sea by polluted rivers may also be factors.