U.S. Water News Online
ST. PETERSBURG, Fla. -- Scientists believe the combination of a large, nutrient-rich patch of runoff combined with a severe outbreak of red tide caused the 60-mile-wide patch of ``black water'' that appeared off the southwest Florida coast in late 2001.
The runoff was stained brown by tannin, decaying vegetation and microscopic plants, scientists said in a recently released report. That, mixed with the discoloration of the red tide algae bloom, likely gave the water its distinctive dark color.
The black patch, large enough to be visible by satellite, mystified scientists and ended up covering hundreds of miles of the Gulf of Mexico from Naples south to Key West and west to the Marquesas.
It was first reported by commercial fishermen who said fish avoided it. Divers said large amounts of coral and sponges died in areas covered by the black water, which appeared in late 2001 and lasted until early 2002.
But researchers are not sure how much effect the area of black water had on coral or sponges.
``We don't see any way to directly attribute the coral deaths to this. We don't have a direct cause and effect,'' said Cynthia Heil of the University of South Florida College of Marine Science.
Toxin from red tide can kill coral, she said. But they don't know that happened in this case.
``There's a lot of debate in the scientific community,'' Heil said.
Scientists do know the black water was not an oxygen-depleted zone devoid of life, like the one in the Gulf off the mouth of the Mississippi River.
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