By Janet Raloff
First in a two part series on dead zones in coastal waters. Part II: “Limiting Dead Zones” is available to subscribers at Limiting Dead Zones.
Summer tourists cruising the waters off Louisiana or Texas in the Gulf of Mexico take in gorgeous vistas as they pull in red snappers and blue marlins. Few realize that the lower half of the water column below them may lack fish, despite the piscine bounty near the surface. For many years now, an annual dead zone has developed in the Gulf, beginning as early as February and sometimes lasting until mid-fall. This zone—water where the oxygen content is so low that denizens can’t survive—tends to leave no surface clue.
Although the precise timing and size of the Gulf’s dead zone varies with the weather, in many years it encompasses 22,000 square kilometers, a parcel of underwater real estate roughly the size of New Jersey. Fish that can evacuate as oxygen drops do so—although abandoning their home habitat may render them vulnerable to predators. Crustaceans and other seafloor life that can’t leave fast enough simply die.