The Gulf of Mexico: The Dead Zone and The Red Tides

A red tide is another name for the phenomena of the algal bloom. A red tide occurs when there is an accumulation of marine algae in the water. These algae are also known as phytoplankton, which is a single-celled, plant like organism. These phytoplankton can form dense patches on the waters surface. When there are high enough concentrations of algae in the water, the water becomes discolored. Not all algae patches are dense enough to discolor the water. The red tides are not associated with tidal movements, which is why the term 'algae bloom' is used.

Starting in 1970, a region on the Gulf of Mexico, which is located in the northern part of the gulf, was recorded as being a 'dead zone'. This occured every 2-3 years due to increased levels of hypoxia. Now the dead zone is an annual thing in the gulf. Each year around spring time, ending around late August or September, the dead zone occurs. It is called the dead zone because oxygen levels are too low to be able to sustain the marine life there.

Phytoplankton, which cause red tides, share a relationship with hypoxia. The presence of nitrogen and phosphorus, along with a disrupted food chain, create favorable conditions for the toxic phytoplankton. Along with the low oxygen levels from the hypoxia, the red tides paralyze the respiratory supply in the water, which kills of more of the marine species.

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~http://www.tulane.edu/~bfleury/envirobio/enviroweb/DeadZone.htm

~http://en.wikipedia.org/wiki/Red_tide