Mysterious Jellyfish Swarms Seen in Europe, U.S.

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Other experts agree the phenomenon is business as usual.

Jellies are seasonal by nature, said Anja Schulze, a marine biologist and assistant professor at Texas A&M University at Galveston.

"Having these blooms at certain times of the year is normal," she said. For example, ocean currents can have effects on populations.

"If the wind is toward the beach, they will end up on the beach," she said.

Voracious Predators

Surges in jellyfish populations are generally only studied after they make a huge impact, Dauphin Island's Graham said.

In 1999, for example, an estimated 50 truckloads-worth of jellyfish filled waters near the Philippines, nearly sparking a political incident.

The swarm clogged water intake vents at a power plant, causing a massive power outage and prompting some locals to fear the country was under a coup d'etat.

Jellyfish explosions can also potentially wreak havoc on ecosystems.

In the 1980s, comb jellyfish invaded the Black Sea and eventually crowded out the native fish population.

"The [comb jellyfish have] become a real problem," Schulze, of Texas A&M, said.

"They are voracious predators. They interfere with the fisheries and clog up the nets. They definitely compete with plankton-eating fish and take over the environment there," she said.

(See a photo of a poisonous giant jellyfish that invaded Japanese waters.)

Overharvesting of fish near the shore creates more hospitable environments for the stinging creatures by removing competition for food, such as phytoplankton and zooplankton.

Altering coastal zones with structures, such as bridges or oil platforms, can also create new habitats.

Jellyfish grow fast, are incredibly adaptive, and seem to benefit from warmer waters, which lead to longer growing seasons and more rapidly appearing blooms, Graham added.

Blistering Mystery

While almost 2,000 species of jellyfish exist, marine biologists know only a handful of them well—mostly because few scientists study jellyfish, said Claudia Mills, a scientist at the University of Washington's Friday Harbor Laboratories.

Natural cycles, however, may be blown out of proportion by news reports that make the situation seem catastrophic, said Mills, who has studied jellyfish for more than 30 years.

"They're all moving and [being] pulsed by nature," she said.

And jellyfish aren't spiking everywhere, she added. In Puget Sound off Washington State, for example, populations of more than 60 species of jellies have decreased during the past 20 years, Mills said.

Ocean currents can skew the perception of population concentrations by making jellies appear closer together, Mills explained.

"The currents change your impression of what's going on," she said.

"The total memory of [jellyfish spikes] is very anecdotal," Mills said. "Presumably it's the availability of food, and [it] might be because of warming temperatures, although there's no scientific evidence to prove that's true."

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