To Know H2O (Water)

Fertilizer runoff and fossil-fuel use lead to massive areas in the ocean with scant or no oxygen, killing large swaths of sea life and causing hundreds of millions of dollars in damage

More bad news for the world’s oceans: Dead zones—areas of bottom waters too oxygen depleted to support most ocean life—are spreading, dotting nearly the entire east and south coasts of the U.S. as well as several west coast river outlets.

According to a new study in Science, the rest of the world fares no better—there are now 405 identified dead zones worldwide, up from 49 in the 1960s—and the world’s largest dead zone remains the Baltic Sea, whose bottom waters now lack oxygen year-round.

This is no small economic matter. A single low-oxygen event (known scientifically as hypoxia) off the coasts of New York State and New Jersey in 1976 covering a mere 385 square miles (1,000 square kilometers) of seabed ended up costing commercial and recreational fisheries in the region more than $500 million. As it stands, roughly 83,000 tons (75,000 metric tons) of fish and other ocean life are lost to the Chesapeake Bay dead zone each year—enough to feed half the commercial crab catch for a year.

“More than 212,000 metric tons [235,000 tons] of food is lost to hypoxia in the Gulf of Mexico,” says marine biologist Robert Diaz of The College of William & Mary in Williamsburg, Va., who surveyed the dead zones along with marine ecologist Rutger Rosenberg of the University of Gothenburg in Sweden. “That’s enough to feed 75 percent of the average brown shrimp harvest from the Louisiana gulf. If there was no hypoxia and there was that much more food, don’t you think the shrimp and crabs would be happier? They would certainly be fatter.”

Oceanic Dead Zones Continue to Spread: Scientific American