Driven by the rapid pace of population growth and economic development, dead zones are a new and largely unstudied problem that is growing more quickly than governments and scientists can keep up with it. Scientists say that in just the past few years, as many as a dozen dead zones have appeared in different areas of the world, all caused by the same combination of agricultural fertilizer and sewage runoff. Five of those zones have so little oxygen that they are on the verge of collapse. One of the five is the area off the Louisiana coast. The dead zone in the Gulf of Mexico waxes and wanes each year, but if it follows the pattern in similar areas, it could become permanent, bereft of oxygen-breathing life, including the valuable fish and shrimp along the coast.
Dead zones start as an infrequent occurrence, showing up every two or three years.
Organisms on the sea floor are suffocated, but soon replaced when the zone breaks up. Then the events become seasonal, as they have in the Gulf, and the ecology of the affected ocean becomes stressed over long periods of time, harming fish and driving fishing boats elsewhere. Fish, shellfish and crustaceans that need oxygen are replaced by forms of bacteria that thrive in a no-oxygen world. Sometimes, perversely, a dead zone can temporarily produce more fish, slowing efforts to fix the problem. By 1984, fishers were catching record amounts at the same time low oxygen levels were being recorded, Diaz said.