Scientists from the National Oceanic and Atmospheric Administration (NOAA) announced last week that the dead zones in the Gulf of Mexico are worse this year than they expected. Four million acres of habitat off the Texas and Louisiana coasts are so oxygen-depleted that fish and other bottom-dwelling species can’t live there.

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Dead zones are more scientifically called “hypoxic zones.” This refers to places where so little oxygen is dissolved in the water that marine species move on, if they’re mobile like fish, or die in place, if they’re less mobile, like oysters. Dead zones happen when agricultural runoff, wastewater or other pollutants overwhelm rivers or coastal areas. The introduced nutrients stimulate algae growth, which then decomposes in the water, a process that consumes oxygen needed by marine life. Dead zones expand and contract with the weather, covering the largest area in summer when water is warmer and oxygen levels are lower.

Related: Underwater robots just discovered the world’s biggest dead zone

“The distribution of the low dissolved oxygen was unusual this summer,” said Nancy Rabalais, Louisiana State University professor and the study’s lead. “The low oxygen conditions were very close to shore with many observations showing an almost complete lack of oxygen.”

Dead zones impact commercial fisheries, such as shrimp in the Gulf of Mexico and crabs and fish in the Pacific Northwest. Oregon has suffered from hypoxic areas every summer since 2002. Scientists said the dead zone developed earlier this year than any other time in the past 35 years. Perhaps as a result, crab fishers have found many Dungeness crab carcasses strewn on Washington and Oregon shores this year.

Fertilizer is one of the main culprits, having caused about $2.4 billion in damage to marine life and fisheries each year since 1980, according to the Union of Concerned Scientists. In 2001, state and federal agencies set a target of 1,900 square miles as the maximum five-year average for the dead zone in the Gulf. This year, the hypoxic area is about three times that size.

“Without a significant, concentrated effort to reduce nitrogen runoff from farms and livestock operations, Gulf Coast communities will continue to bear the costs of the dead zone,” said Rebecca Boehm, an economist with the Union of Concerned Scientists. “The dead zone has not meaningfully shrunk in the last 30 years, and we are no closer to the goals set by the Hypoxia Task Force. Policymakers need to rethink their strategy, or we will find ourselves back here next year with the same bad news.”

Via The Guardian, NOAA

Lead image via Pixabay