Experts find life in 'black water'

Marine scientists suspect the mass of discolored water in the gulf west of the Florida Keys is not a dead zone but the result of an algae bloom.

By CRAIG PITTMAN, Times Staff Writer
© St. Petersburg Times
published March 29, 2002

ST. PETERSBURG -- Some of the state's top marine scientists gathered Thursday to discuss the much-publicized "black water" phenomenon that appeared off the Southwest Florida coast recently and swept toward the Keys.

Their conclusions: It's not a dead zone where nothing lives, as some fishermen have feared. The water may not even be black. And whatever it is does not appear to have been caused by pollution or pose a threat to human health.

Its effect on marine life, however, remains to be seen, since there are reports coming in of dead sponges in the Keys, the area where the phenomenon has been seen most recently.

But those deaths could be the lingering aftereffect of a Red Tide outbreak, said Karen Steidinger of the Florida Marine Research Institute. Steidinger is such an expert on Red Tide that the microorganism now carries a Latin version of her name, Karenia brevis.

Steidinger and other experts from the University of South Florida and Mote Marine Laboratory said they suspect the mass of discolored water has resulted from an algae bloom of some sort.

One strong possibility is a microorganism called Rhizosolenia, which was found in medium concentrations in two different patches of water -- one of them described as "nasty" by a volunteer -- near Key West on March 16.

Rhizosolenia also dominated samples from 11 spots between Key West and Sugarloaf Key that were checked March 19. In that area the water appeared darker green than usual.

Under a microscope, Rhizosolenia looks like thousands of toothpicks. A thick bloom could clog the gills of fish and deplete oxygen in the water, also causing distress to marine life.

Rhizosolenia blooms have previously been identified as the cause of brown surface discoloration along the western edge of Florida Bay, which is near the current black water patch. They are "fairly common" this time of year in that area, Steidinger said.

The scientists spent some time Thursday discussing whether the black water is really black or if it could be brown, green or something in between.

Their research will continue over the next few weeks, although the discolored patch already appears to be breaking up.

In the early 1990s, a large dead zone was discovered off the coast of Louisiana, thought to be caused by Mississippi River water that carried high concentrations of fertilizer and waste material from animals and humans. Because the water in the 8,000-square-mile area lacks dissolved oxygen, it cannot support sea life.

But the black water off the Keys is no dead zone, the scientists said Thursday. There appears to be sufficient dissolved oxygen, at least during the daytime when samples have been taken. And microscopic plants called phytoplankton, the foundation of the marine food chain, turned up in the samples.

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