The upside-down world of the Gulf’s dead zoneBy Robynne Boyd for mnn.com
December 10, 2015
Farming runoff turns the sea floor into a wet desert and forces species onward or upward.
Stirred up ocean sediment in the Gulf of Mexico. Adding the range of colors in the picture are nutrients like iron from soil and nitrogen from fertilizers. These nutrients fuel the growth of phytoplankton that color the ocean blue and green. (Photo: Jeff Schmaltz/NASA Earth Observatory/Wikimedia Commons)
The seas off the Gulf of Mexico look much like any stretch of ocean — an expanse of mercurial waves shimmering and sparkling in sunlight — except for the greenish tint. Below the surface, it’s a vastly different story owing to a problem that’s suffocating the sea.
For marine ecologists like Nancy Rabalais, diving here is like entering an upside-down world where the water column has been turned on its head. The barnacles and sponges usually found on the seabed now cling to oil rig platforms where Atlantic spadefish, triggerfish, snapper and larger pelagic predatory fish hide and hunt.
The hypoxic zone, or "dead zone," in the Gulf of Mexico occurs in the summertime when the concentration of dissolved oxygen in the water becomes too low to support marine life. As a result, the seafloor that once housed snails, worms, starfish and bivalves has morphed into a wet, lifeless desert. The more mobile species, like fish, shrimp and crabs, move onward or upward.