Florida's "Red Tide" Mystery Tied to Mississippi River

Randolph E. Schmid
Associated Press
November 8, 2007

Scientists have figured out why harmful "red tide" blooms form along Florida's western coast every fall. The knowledge may help them to make better predictions about when the algae will appear and how bad it will be.

Seasonal changes in wind patterns move fertilizer and other nutrients east from the Mississippi River, a group of researchers reported Wednesday.

The team led by Richard P. Stumpf of the National Oceanic and Atmospheric Administration (NOAA) concluded that nutrients from the Mississippi were encouraging the blooms, which occur along fronts of changing water density in the ocean. Changes in temperature or salinity can result in differing water density.

The destructive algal blooms occur from time to time in most coastal areas, with different algae affecting different areas.

Florida's blooms, which tint the coastal waters reddish brown, are caused by an organism called Karenia.

Karenia can swim up and down in the water, allowing them to feed on deep nutrients and then return to the surface, where they get light and form toxic blooms, Stumpf explained at a news conference.

Now that they have found the algae congregating below the surface, scientists are experimenting with an underwater mechanism to detect the blooms before they come to the surface.

"The key goal is to do a better forecast," Stumpf said.

Nationwide, NOAA reports, harmful algal blooms have a direct economic impact estimated to average 75 million U.S. dollars annually. That sum includes public health costs, commercial-fishing closures, recreation and tourism losses, and management and monitoring costs.

Scientists had been puzzled about why the west Florida blooms formed in water that is normally low in the nutrients that the algae live on.

"We found that the concentrations of nutrients needed to start the Florida red tides is much lower than previously suspected," Stumpf said. "The hypothesis means that offshore areas should be examined for both small increases in nutrients and modest concentrations of the algae at the start of the bloom season."

Normally water from the Mississippi travels west, he explained, but seasonal wind changes in late summer and fall move it eastward toward Florida.

Findings of the research team are published in the journal Continental Shelf Research.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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