Published December 27, 2008 08:50 AM

It's 'attack of the slime' as jellyfish jeopardize the Earth's oceans

It has been dubbed the "rise of slime." Massive swarms of jellyfish are blooming from the tropics to the Arctic, from Peru to Namibia to the Black Sea to Japan, closing beaches and wiping out fish, either by devouring their eggs and larvae, or out-competing them for food.

To draw attention to the spread of "jellytoriums," the National Science Foundation in the U.S. has produced a report documenting that the most severe damage is to fish: In the Sea of Japan, for example, schools of Nomurai jellyfish - 500 million strong and each more than two metres in diameter - are clogging fishing nets, killing fish and accounting for at least $20-million in losses. The Black Sea has suffered $350-million in losses. A region of the Bering Sea is so full of jellies that it was nicknamed "Slime Bank."

Though the reasons for the rise of jellyfish vary from region to region, in many cases we have ourselves to blame, says Richard Brodeur, an NSF scientist and research fishery biologist with the U.S. National Oceanic and Atmospheric Administration.


In some oceans, climate change is fuelling their growth "because a lot of jellies grow faster and produce more young in warmer waters," Dr. Brodeur says. In other places, overfishing of large predatory fish such as tuna is the main cause. A major problem, he says, is the introduction of new species - such as those in the Black Sea - through the release of ballast water from regions as far away as the Great Lakes.

Farming is also an issue: Fertilizer runoff causes algae to bloom, soaking up the water's oxygen and rendering vast areas inhospitable to almost all life - except jellyfish, which "can survive in very low-oxygen conditions where fish cannot," Dr. Brodeur says. The result is "dead zones," more than 400 worldwide, covering 25,000 hectares, the NSF says

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