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Jellyfish Blooms Not Caused By Global Warming And Overfishing Of Competitors, Study Suggests

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They've shut down power stations and terrorized beachgoers. But does a surge in stories about jellyfish wreaking havoc really point to a man-made surge in the creatures themselves?

A new study in BioScience says it doesn't.

The study, by Robert H. Condon of Dauphin Island Sea Lab and 16 co-authors, denies the media's now standard contention that jellyfish population booms (called blooms) are caused by humans. According to a BioScience statement, the study suggests that "the perception of an increase is the result of more scientific attention being paid to phenomena such as jellyfish blooms and media fascination with the topic."

Condon, et al., note that the data doesn't support such a conclusion:

"Clearly, there are areas where jellyfish have increased — the situation with the Giant Jellyfish in Japan is a classic example," said Condon. "But there are also areas where jellyfish have decreased, or fluctuate."

The "situation with the Giant Jellyfish in Japan" Condon mentions was a 2009 bloom of large Nomura's jellyfish off Japan's west coast. The events that followed, including a 10-ton fishing boat sinking while hauling in a net full of the massive creatures, made this bloom a turning point in the public perception of the jellyfish problem.

Condon and his co-authors acknowledge that researchers disagree over the best way to interpret jellyfish data, according to a statement from BioScience.

"They point out that changes in populations of jellyfish and similar sea organisms do have important consequences for local marine ecology and could be affected by human activity. For that reason, they are assembling a comprehensive new database that will enable trends in the numbers of such creatures to be assessed and the links to human activity studied. But for now, Condon and his co-authors believe the case for jellyfish-dominated seas in coming decades is not proven."

"This is the first time an undertaking of this size on the global scale has been attempted, but it is important to know whether jellyfish blooms are human-induced or arise from natural circumstances," said Condon.