For the eighth successive year, the resorts of the north Mediterranean coast are threatened by a monstrous-looking primeval creature from the depths, the jellyfish.
Although injuries to bathers have been rare, marine biologists have spotted vast shoals of "mauve stingers" or Pelagia noctiluca in the waters between Corsica and the French mainland. From next week, the town of Cannes will erect booms and nets around its most popular beaches to try to protect bathers from the nasty, but rarely fatal, burn-like sting of the invaders.
An aerial survey, Jellywatch, is also under way off the Italian and Greek coasts to try to monitor the movements of the jellyfish, which are not fish but a a kind of giant plankton. Scientists say the large eruption of Pelagia noctiluca this summer is final proof of a radical, and possibly irreversible, change in the ecology of the Mediterranean.
For centuries, plagues of jellyfish have come inshore every 10 or 12 years and lingered along the Côte d'Azur for periods of about four years. This pattern has now changed. The jellyfish have appeared each year for the past eight years in far greater numbers than before. Some scientists and ecological campaigners point to a rise in sea temperature, linked to the warming of the planet. Others blame a shortage of natural predators such as the bluefin tuna and the turtle, which have been driven almost to extinction by overfishing and pollution.
Professor Gabriel Gorsky of the Observatoire Océanographique at Villefranche-sur Mer, also points to changes in the wind and current patterns, changes which may also be linked to global warming. Jellyfish live deep in the sea during the day but rise to the surface at night to feed. Abrupt changes in wind and current can then carry them onshore. Denis Ody of the World Wildlife Fund, based in Marseilles, said: "I was on the sea between Corsica and the mainland two weeks ago and for several hours we passed through immense areas where you could count 60 jellyfish a minute."
This year's jellyfish invasion coincides with a row between the European Commission and the French government and fishermen about alleged overfishing of bluefin tuna in the Mediterranean. Brussels ordered the fishery to close last week after calculating that the whole of the 2008 quota for European boats had already been caught. Paris is pushing for an "emergency" reopening of the fishery. Marine biologists warn that this could not only threaten the survival of the tuna; it could also prove uncomfortable for holidaymakers.