WASHINGTON The number of oxygen-starved "dead zones" in the world's seas and oceans has risen more than a third in the past two years because of fertilizer, sewage, animal waste and fossil-fuel burning, United Nations experts said Thursday.
Their number has jumped to about 200, according to new estimates released by U.N. marine experts meeting in Beijing. In 2004, U.N. experts put the estimate at 149 globally.
The damage is caused by explosive blooms of tiny plants known as phytoplankton, which die and sink to the bottom, and then are eaten by bacteria, which use up the oxygen in the water.
Those blooms are triggered by too many nutrients particularly phosphorous and nitrogen.
The U.N. report estimates there will be a 14 percent rise in the amount of nitrogen that rivers are pumping into seas and oceans globally over a period from when the levels were measured in the mid-1990s to 2030.
Oxygen starvation robs the seas and oceans of many fish, oysters, sea grass beds and other marine life and the number of such dead zones has grown every decade since the 1970s.
Not all of them persist year-round, as they do in the Gulf of Mexico, where the Mississippi River pours its fertilizers and other nutrients.
Some dead zones return each summer, depending on winds that generate upwelling, in which nutrient-rich water is brought to the surface from lower depths.
But all the dead zones pose a danger to global fish stocks, which many marine scientists say are increasingly hammered by overfishing and pollution.
Dead zones first were reported in the United States' Chesapeake Bay; the Baltic Sea; the Kattegat bay in the North Sea; the Black Sea; the northern Adriatic Sea; and some Scandinavian fjords.
Others have appeared off South America, China, Japan, southeast Australia and New Zealand, according to U.N. research led by Robert Diaz, a marine scientist at Virginia's College of William & Mary.
Diaz and his team reported finding new dead zones in Finland's Archipelago Sea; Ghana's Fosu Lagoon; China's Pearl River estuary and Changjiang River; Britain's Mersey River estuary; Greece's Elefsis Bay and Aegean Sea; Peru's Paracas Bay; Portugal's Mondego River; Uruguay's Montevideo Bay; and the Western Indian Shelf.