WASHINGTON Like a chronic disease spreading through the body, "dead zones" with too little oxygen for life are expanding in the world's oceans.
"We have to realize that hypoxia is not a local problem," said Robert J. Diaz of the Virginia Institute of Marine Science. "It is a global problem and it has severe consequences for ecosystems."
"It's getting to be a problem of such a magnitude that it is starting to affect the resources that we pull out of the sea to feed ourselves," he added.
Diaz and co-author Rutger Rosenberg report in Friday's edition of the journal Science that there are now more than 400 dead zones around the world, double what the United Nations reported just two years ago.
"If we screw up the energy flow within our systems we could end up with no crabs, no shrimp, no fish. That is where these dead zones are heading unless we stop their growth," Diaz said in a telephone interview.
The newest dead areas are being found in the Southern Hemisphere South America, Africa, parts of Asia Diaz said.
Some of the increase is due to the discovery of low-oxygen areas that may have existed for years and are just being found, he said, but others are actually newly developed.
Pollution-fed algae, which deprive other living marine life of oxygen, is the cause of most of the world's dead zones. Scientists mainly blame fertilizer and other farm run-off, sewage and fossil-fuel burning.
Diaz and Rosenberg, of the University of Gothenburg in Sweden, conclude that it would be unrealistic to try to go back to preindustrial levels of runoff.
"Farmers aren't doing this on purpose," Diaz said. "The farmers would certainly prefer to have their (fertilizer) on the land rather than floating down the river."
He said he hopes that as fertilizers become more and more expensive farmers will begin seriously looking at ways to retain them on the land.
New low-oxygen areas have been reported in Samish Bay of Puget Sound, Yaquina Bay in Oregon, prawn culture ponds in Taiwan, the San Martin River in northern Spain and some fjords in Norway, Diaz said.
A portion of Big Glory Bay in New Zealand became hypoxic after salmon farming cages were set up, but began recovering when the cages were moved, he said.
A dead zone has been newly reported off the mouth of the Yangtze River in China, Diaz said, but the area has probably been hypoxic since the 1950s. "We just didn't know about it," he said.
Some of the reports are being published for the first time in journals accessible to Western scientists, he said.
Nancy N. Rabalais, executive director of the Louisiana Universities Marine Consortium, said she was not surprised at the increase in dead zones.
"There have been many more reported, but there truly are many more. What has happened in the industrialized nations with agribusiness as well that led to increased flux of nutrients from the land to the estuaries and the seas is now happening in developing countries," said Rabalais, who was not part of Diaz' research team.
She said she was told during a 1989 visit to South America that rivers there were too large to have the same problems as the Mississippi River. "Now many of their estuaries and coastal seas are suffering the same malady."
"The increase is a troubling sign for estuarine and coastal waters, which are among some of the most productive waters on the globe," she said.