Monsters of the Deep: Jellyfish Threaten the World's Seas

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"We are used to jellyfish in the Mediterranean," says Gili, 60, a short, gray-haired man. "But what we have observed here in the last few years is no longer normal." Pelagia noctiluca, for example, doesn't swim from the open sea toward the coast of its own volition. Instead, it is driven by waves and currents, dying where it goes aground. In the Mediterranean, this fate has typically befallen mauve stingers about once every 10 to 15 years. But now the blooms have been happening with much greater frequency, with similar incidents occurring in 2005, 2006, 2007, 2011, 2012 and 2013.

The European Union has also begun to show concern over the frequent jellyfish invasions, which present an additional burden on the already ailing economies of its southern member states. That's why the EU is now funding an international research project that will gather data on the spread of jellyfish in the Mediterranean region for the first time, as well as develop a coastal management strategy. The scientists involved in the project plan to test such strategies as protective nets along beaches and a smartphone app that would enable beachgoers to report jellyfish sightings.

The impetus from Brussels was overdue. Scientists still know little about jellyfish, because the animals are difficult to study. They appear suddenly and unpredictably, as if out of nowhere but in large numbers. But for scientists hoping to collect the creatures and study them in laboratories, jellyfish are difficult to keep alive. Breeding jellyfish in an aquarium is also a complicated undertaking. These obstacles help to explain why there is only a small community of jellyfish experts worldwide.

Gili no longer knows exactly why he decided, years ago, to study jellyfish. Perhaps he found them interesting because he grew up with them, on the island of Mallorca. "When I was young, my father used to rub olive oil on my body before I went swimming, to protect me from jellyfish injuries," he recalls with a smile. "Olive oil is the best protection. A lot of sunscreen also helps."

He and his colleague Verónica Fuentes, 35, are in charge of implementing the EU project in Spain. The most important thing, says Gili, is to educate people. "We tell the tourists that they should come to our country because the Mediterranean is fantastic," he says, "but we also have to let them know that the sea is not a swimming pool. You can enjoy the sun and the warm water here, and sometimes there happen to be jellyfish in the water. You have to be prepared for that."

A Global Problem It isn't just a problem in the Mediterranean, but worldwide. Especially in late summer, swimmers in the North and Baltic Seas often encounter lion's mane jellyfish, which are known as "fire jellyfish," and for good reason. Their stringy stinging tentacles are often the color of flames. Far more common in the region are blooms of milky-blue moon jellyfish, which, like the majority of jellyfish species, do not inflict pain on human beings.

Compass and crystal jellyfish now dominate the coastal waters of Namibia, where sardines were once abundant. And since the mid-1990s, fishermen in the East China Sea and the Yellow Sea have complained that their nets are being filled with more and more jellyfish and fewer and fewer fish.

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