WASHINGTON - Like a chronic disease spreading through the body, dead zones with too little oxygen for life are expanding in the world's oceans.
"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 because of 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.
The Puget Sound region's best-known dead zone crops up frequently at this time of year in southern Hood Canal. There, sunlight and high levels of nitrogen fuel blooms of algae that die, robbing the water of oxygen as they are eaten by bacteria, causing the fish to die out. The most recent big fish kill, in 2006, involved Dungeness crabs, shrimp and several species of finfish.
Sources thought to be contributing the nitrogen that drives Hood Canal's algae blooms are fertilizers, leaking septic tanks, ocean water and alder trees that pop up on vast patches of clearcut forest.
Less well known is an intense focus by state officials and others on southern Puget Sound proper, where some scientists fear oxygen levels are dropping low enough in some bays to soon provoke a similar cycle.
Off the coast of Washington and Oregon, recent years have seen a dead zone appear nearly annually, apparently associated with anomalies in wind patterns that boosted the levels of nitrogen.
That set off a cycle much like Hood Canal's.
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."
"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.
"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.