RENEE MONTAGNE, HOST:
On Mediterranean beaches, there's been a spike in the number of jellyfish this summer. It's so bad the British government has put out a warning to its citizens vacationing near those waters. Scientists blame overfishing and possibly climate change. Lauren Frayer reports on efforts to take the sting out of swimming.
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LAUREN FRAYER, BYLINE: Blue turquoise waves lap at white sand here on the Spanish island of Formentera in the Mediterranean. The beach is crammed with sweaty tourists from all over Europe. But this particular afternoon, no one dares take a cool dip in the water. The reason? It's what Spaniards call medusas - named after that monster from Greek mythology with a woman's face and venomous snakes for hair. In English, we call them jellyfish.
GABRIELLE AMAND: It's very small, very small. You see? We can see one, a little one.
FRAYER: The red one?
AMAND: Yeah, the pink - yes, the little red thing. Yes. It hurts a lot. He cried a lot, a lot.
FRAYER: Gabrielle Amand, on vacation from France, has her son wrapped in a towel under an umbrella after he was stung.
AMAND: He doesn't want to go again.
FRAYER: Santiago Sanchez and his college buddies from Madrid have been coming here for summer vacation for 14 years. They charter a boat, sleep out at sea, and swim into sheltered crystal-clear coves. Unfortunately so do the jellyfish.
SANTIAGO SANCHEZ: I was swimming from the boat and I think I passed by around five of them. Just the small ones, but I think I got stung on my arm. It's a little bit hot and, you know, it feels like scratching all the time. But it's not, not too bad, actually.
FRAYER: Will you go back in the water again, or...
SANTIAGO SANCHEZ: I think I'd rather go back in the dinghy.
FRAYER: Up to 100,000 people are treated for jellyfish stings on Mediterranean beaches each year. And scientists say that number is on the rise. Along some stretches of Spain's coast, they've spotted huge, mile-long blooms of jellyfish, sometimes with 30 to 40 animals per square yard of sea.
Marine biologist Stefano Piraino, from Italy's University of Salento, is just back from a flyover of 200 miles of Mediterranean coast to monitor growing jellyfish populations. He thinks he knows the reason.
STEFANO PIRAINO: Over fishing is one reason, because if we take out the fishes from the oceans, we leave more food in the environment, and jellyfish are very smart. They can multiply very easily in a very short time; much faster than any vertebrate, any fish in the sea.
FRAYER: Piraino says he believes research will eventually show that climate change is also to blame.
PIRAINO: Many of the species we are observing have a faster growth rate with increased temperature. There are a number of alien species coming from the Red Sea, so tropical and subtropical species that have entered the Mediterranean Sea from the Suez Canal.
FRAYER: That includes the Rhopilema nomadica, a stinging jellyfish that's been sighted in the eastern Med, near the warm-water gateway of Egypt's Suez Canal. The European Union considers it one of the most invasive marine species on the continent. Most jellyfish in the Mediterranean do not sting though and those that do aren't life-threatening. But they can hurt tourism, a major source of revenue for Spain and other coastal countries. Britain's foreign office put out a jellyfish warning to its citizens holidaying on the Med this summer.
The Amand family, from France, is even thinking of cutting short their vacation.
AMAND: We want to stay 14 days, but argh - if we can't swim every day, yes. Well, we won't come back. But I don't know. I hope it will be OK.
FRAYER: In addition to red, yellow and green flags that indicate whether it's safe in general to swim, Spain has also introduced jellyfish warning flags on some beaches. Scientists on Israel's Mediterranean coast are experimenting with sound frequencies that could disrupt jellyfish patterns.
But the Italian scientist Piraino says he doesn't want to scare tourists, he wants to recruit them. He's developed a smartphone app on which people can report jellyfish outbreaks.
PIRAINO: If you are on the beach and if you see some jellyfish, you can even send us a picture. And in the last three years, we received around 10,000 records from citizens. You can imagine that if the same campaign would have been carried out with scientific boats or personnel, this would have cost an enormous amount of money.
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FRAYER: Back on the beach, as the water warms toward the end of summer, even more jellyfish may soon be washing ashore.
For NPR News, I'm Lauren Frayer.
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