Gulf Dead Zone Looks Smaller, but Appearances Deceive

By By Brandon Keim, Wired Science at
July 28, 2009

The infamous Gulf of Mexico dead zone looks smaller than predicted this year, but scientists say the reprieve is just temporary, and barely even a reprieve. Some worry that more pollution could cause the Gulf’s ecosystem to collapse.

“We’re in a condition in the Gulf of Mexico that indicates we might be near some sort of tipping point, but you don’t really know it until it happens,” said Nancy Rabelais, director of the Louisiana Universities Marine Consortium.

The federal National Oceanic and Atmospheric Administration released the dead zone data Tuesday. Caused by farm fertilizer runoff that feeds algae that in turn feeds oxygen-gobbling bacteria, the dead zone has covered an area the size of New Jersey for the last several years. This year, unexpected weather patterns — rather than a drop in pollution — have cut its surface area by half.

“The models do not include weather,” said Robert Diaz, a Virginia Institute of Marine Science biologist who’s tracked ocean dead zones since 1995.

But oxygen levels are unusually low, and run especially deep, in the afflicted area. Bottom-dwelling crab, shrimp and eels have been found swimming on the ocean surface. Elsewhere in the Gulf, phytoplankton distribution has changed, and deep-sea creatures have given way to those that can survive high in the water column.

Rabelais and other researchers have found that the effects of nitrogen are becoming more pronounced, with small doses generating the same low-oxygen volumes once produced by large amounts of pollution.

Whether these changes are potentially stable or signify the wobbling of a system that could suddenly shift to a radically different ecological structure is hard to tell.

“Where we are in this continuum in the Gulf of Mexico, we don’t know. There are other areas where fisheries have collapsed. I’m not saying that’s going to happen in the Gulf of Mexico, but we’re concerned,” said Rabelais. “We’re in experimental mode here.”