UNEP: Ocean 'dead zones' growing

The number of "dead zones" in the world's waters has grown to 200 sites in 2006, the United Nations Environment Programme (UNEP) announced Thursday.

That is a significant increase from the 149 dead zones identified in 2004, according to the reports released by UNEP scientists.

So, what exactly is a dead zone, and why should this concern everyone?

A dead zone is a sea or ocean area low in oxygen. It's full of algal blooms--fast-growing populations of phytoplankton algae that cause oxygen depletion and a growth of toxic bacteria once they die.

Algal blooms are caused by pollutions like sewage, fertilizer run-off and deposited fossil fuel emissions, UNEP said in a statement.

An increasing number of dead zones is bad news for the economic chain, as well as the food chain, according to UNEP, since a lack of oxygen and introduction of toxins into the waters means fewer fish, shellfish, and ocean vegetation.

The Gulf of Mexico, one of the first dead zones to be identified, is caused by the deposit of fertilizer run-off brought down by the Mississippi River, said UNEP. The phenomenon is commonly referred to as "red tide."

Newly identified dead zones now include areas of the Pearl River Estuary and the Changjiang River in China, the Aegean Sea in Greece, and the Mersey Estuary in the United Kingdom.

A full list of new dead zones will be available in 2007 from the UNEP's marine research branch. The research team is led by Professor Robert Diaz of the College of William and Mary.