Jellyfish: A Gelatinous Invasion

Marco Putti

Trouble at sea The Mnemiopsis thrives in waters that have been overfished

The jellyfish in the photos didn't look like they'd pose a danger to swimmers. Thinly veined and translucent, they didn't have stinging tentacles trailing behind them or dramatic colors signaling danger. But Ferdinando Boero, a professor of zoology at the University of Salento in Italy, knew that they meant trouble nonetheless.

The pictures, sent by a biologist in the northern Italian town of Lerici in July, marked the first time the species Mnemiopsis leidyi, a thumb-size jellyfish known as the sea walnut, had been documented in the western Mediterranean Sea. Native to the Atlantic coast of the U.S.,...

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