As the summer comes to an end a disturbing sign of environmental imbalance is washing up on many of the world's beaches: a jellyfish invasion.
Swarms of small, not entirely friendly creatures, are forcing beach closings from the Mediterranean to Australia.
"There were beautiful summer days when you couldn't swim," said Amy Dolan who was enjoying a day at the beach in Falmouth, Mass. "You wouldn't even want to go in the water. You wouldn't want your kids to go in the water. … It ruined the summer day."
Dolan says her children have been stung by jellyfish several times this year, much more frequently than in previous summers.
"The lifeguards were going in the water with nets, fishing out hundreds of jellyfish," Dolan said.
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Lifeguards in Cape Cod, Mass., keep bottles of vinegar on hand to soothe stings.
"In the past I'd say maybe one or two every day would come with jellyfish stings and now there has to be at least on average 10 a day," said Mark O'Connell, a lifeguard in Falmouth.
While there is no organization keeping an official count, reports from around the world have convinced scientists the jellyfish population is exploding.
"Jellyfish do seem to be increasing all over the world in more places than they've ever been before and in greater numbers than they've ever been before," said Marine biologist Larry Madin who has been researching jellyfish for 30 years.
Scientists say it is a sign that the health of the oceans is deteriorating and warn that mass extinctions of marine life could be coming.
"It's kind of a canary in a coal mine as to what might be coming next. Are the oceans going to be getting much worse?" Madin asked.
Marine biologists say there are several possible reasons for the ocean's decline. As global warming raises the water's temperature jellyfish breed faster. And they have fewer predators thanks to the fishermen who catch tuna and swordfish. Pollution also plays a role in upsetting the delicate balance of the ocean's ecosystem.
"It's not only jellyfish that are a symbol of this," said Madin. "Probably we'll see more red tides, blooms of algae, which are due to the same factors. We're upsetting the balance that used to exist in the ocean, and it's finding a new balance that includes more jellyfish."
Jellyfish are known as survivors who actually thrive in damaged environments. That's how they earned their nickname as the "cockroaches of the ocean." They are primitive creatures that have no brain, can't see and are composed almost entirely of water. They have also been around for hundreds of millions of years, and if things start to go wrong in the ocean, jellyfish are the likely ones to pull through.
"They're going to be long-term survivors and will be in the ocean long after we're gone," said Madin.
Scientists say it's likely we're going to see even more jellyfish in summers ahead, so beach-goers will need to learn how to peacefully co-exist with such nettlesome neighbors.