Ocean Dead Zones Going Global

Aug. 14, 2008 -- 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.