Mysterious Jellyfish Swarms Seen in Europe, U.S.

Kimberly Johnson
for National Geographic News
August 11, 2008
The recent dramatic increases in jellyfish swarms along Atlantic and Mediterranean coasts highlight the need for more research into the life cycles of these stinging invertebrates, experts say.

Jellyfish are found along most coasts worldwide. The animals reproduce quickly, though populations typically recede during fall and winter months.

Recent news reports point to sharp increases in jellyfish blooms along New Jersey's Atlantic Coast and in the Mediterranean Sea.

(Read: "Jellyfish Invasion Puts Sting on Europe Beaches" [August 18, 2006].)

The phenomenon points to just how little is known about jellyfish, scientists say.

"Data do not exist to say if it's a long-term trend," said Monty Graham, a marine biologist at Alabama's Dauphin Island Sea Lab.

Empirical evidence is scattered and tricky to interpret, Graham wrote in a recent commentary in the journal Marine Scientist.

"Yet there is enough cumulative evidence to suggest real long-term increases in jellyfish have occurred in a number of ecosystems."

Making Headlines

A lack of hard data can skew the impact of seasonal blooms, experts warn.

While recent local news reports say that jellyfish are pushing their way inland into New Jersey bays and rivers, one expert said it's not a pronounced problem.

"We as an agency don't have any ongoing studies or data to support that there is an increase in the jellyfish population," said Elaine Makatura, spokesperson for the New Jersey Department of Environmental Protection.

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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