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.
What can be done about it? "In some cases, introducing other species that prey on the jellies can control them," Dr. Brodeur says, but we have to proceed with extreme caution, as thsi risks trading one problem for another.
Origins of climate change
It has been a controversial idea from the start: Did man-made global warming actually start 10,000 years ago?
William Ruddiman of the University of Virginia first proposed the idea in 2003. Last week, Stephen Vavrus, a climatologist at the University of Wisconsin-Madison's Center for Climatic Research, presented supporting data, gathered with Prof. Ruddiman, to the American Geophysical Union.
The theory posits that the Earth has swung between ice ages and warm temperate interglacial periods for the past million years, with each shift triggered by regular changes in the Earth's orbit around the sun and fuelled by "positive feedback" effects - such as the loss of ice and snow, which reflect sunlight back to space, and the increase in darker-coloured, less reflective water, soaking up heat and further warming the planet (as is happening right now).
About 5,000 to 8,000 years ago, levels of the greenhouse gases carbon dioxide and methane started to rise more than the levels typical of other post-ice-age periods, based on ice-core records from Antarctica. According to Prof. Ruddiman, the change was caused by human activities, such as clearing forests in Eurasia, releasing carbon dioxide and cultivating rice paddies in Asia, releasing methane. Global warming was promoted by the resulting positive feedback effects - warming the oceans, for example, which lowered their carbon dioxide content (cold liquids, like champagne, hold more gas than warm ones). Even before the start of the Industrial Revolution, the scientists say, levels of methane and carbon dioxide were already accelerated.
Prof. Vavrus presented data from computer simulations done with Prof. Ruddiman. "As computers improve, we can make more sophisticated models that incorporate more and more of the feedback effects together."
