Massive marine dead zone forms in Gulf of Mexico
Pastor Dale Morgan
Massive marine dead zone forms in Gulf of Mexico*
JANET MCCONNAUGHEY IN NEW ORLEANS
THE world's second largest "dead zone" has formed in the sea off the
Louisiana and Texas coasts, according to scientists.
Crabs, eels and other creatures usually found on the bottom of the Gulf
of Mexico are swimming in crowds on the surface because there is too
little oxygen in their usual habitat, said Dr Nancy Rabalais of the
Louisiana Universities Marine Consortium.
At 7,900 square miles, the oxygen-poor area is not quite as big as was
predicted for this year, but it is still the third-largest ever mapped.
"We very often see swarms of crabs, mostly blue crabs and their close
relatives, swimming at the surface when the oxygen is low," Dr Rabalais
said from a research ship as it returned to Cocodrie, Lousiana from its
annual measurement trip.
But she added that eels, which usually live in sediments 60ft-70ft under
water, were a less common sight on the surface.
The Gulf of Mexico annually develops a vast "dead zone" when the supply
of oxygen shrinks, causing hypoxia.
This year's is about 7.5 per cent smaller than had been predicted by
Eugene Turner, a professor of oceanography and coastal sciences at
Louisiana State University, from his judging of nitrogen content in the
Mississippi River watershed.
He had predicted it would be about 8,540 square miles, which would have
made it the largest dead zone measured in at least 22 years.
More storms than normal may have reduced hypoxia by keeping the waters
churning, Dr Rabalais said.
Hypoxia occurs in the Gulf when fresh water pouring in from the
Mississippi floats above the heavier salt water. Algae die and fall to
the bottom, where their decay uses up oxygen faster than it can be
replenished by being brought down from the surface. Eventually, the
lower layer holds too little oxygen for aquatic life.
Nitrogen, from fertilisers, erosion and sewage, speeds up the process by
feeding algae.
The Gulf's dead zone was larger in 2002 and 2001, covering 8,500 square
miles and 8,006 square miles respectively.
Dead zones have appeared elsewhere in the United States, and have been
reported off South America, China and Japan, and in the Baltic and Black
seas.