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Swimming Danger

DW staff (th)July 5, 2008

Jellyfish are taking over Europe's favorite swimming spots in increasing numbers. Scientists blame climate change and overfishing for the proliferation of the stinging nuisance.

Three jellyfish in the water
Some jellyfish have a nasty stingImage: picture-alliance/dpa/dpaweb

While Mediterranean resort areas will be hardest hit by the jellyfish plague this summer, there will also be high concentrations in the Baltic and North Seas, according to scientists. They warn that the dramatic increase in jellyfish is a sign that ocean ecosystems are out of whack.

"Jellyfish are an excellent bellwether for the environment," Jacqueline Goy of the Oceanographic Institute of Paris told AFP news agency. "The more jellyfish, the stronger the signal that something has changed."

Jellyfish are a problem because their tentacles, used to paralyze prey, cause burning rashes when they come into contact with humans.

Warm waters, overfishing blamed

People sunbathe on the beach in Italy
Stinging jellyfish take the fun out of swimmingImage: AP

Overfishing is one cause for the explosion in jellyfish populations, said Ricardo Aguilar, research director for the non-governmental organization Oceana. Jellyfish predators such as tuna, sharks and turtles are disappearing. The lack of predators also means a lack of competition for plankton and small fish, which make up the jellyfish diet.

The other cause for the population increase is global warming as higher water temperatures prolong their reproductive cycles.

"Jellyfish have come to occupy the place of many other species," Aguilar told AFP.

Numbers staying high

Researchers examine jellyfish
Marine biologists are worried about the increaseImage: DW

It used to be that jellyfish would arrive inshore once every decade, stay for a few years, and then go in to a period of decline. Yet for the past eight years, jellyfish numbers have been steadily increasing with no signs of dropping off. Once the population explodes, it might be hard to control, marine biologists say.

This summer, marine biologists have already spotted swarms of jellyfish in the waters between Corsica and the French mainland. Cannes, France plans to install booms and nets around its most popular beaches to keep the jellyfish at bay, according to The Independent newspaper.

Scientists have also started a jelly-watch off the Italian and Greek coasts to monitor the movements of the jellyfish, the newspaper reported.

Fishing remains a highly politicized topic in Europe. The European Union recently ordered a halt on blue fin tuna fishing in the Mediterranean, saying that the entire 2008 quota had already been caught.

The French government is pushing for the fishery to reopen on an "emergency basis." Marine biologists have warned that this could further exacerbate the jellyfish population.