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Rob Gutro                   April 17, 2003
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 301-286-4044)
Rgutro{at}pop900.gsfc.nasa.gov

Release: 03-39

BLACK WATER TURNS THE TIDE ON FLORIDA CORAL

In early 2002, a patch of "black water" spanning over 60 miles in 
diameter formed off southwestern Florida and contributed to severe 
coral reef stress and death in the Florida Keys, according to results 
published from research funded by NASA, the U.S. Environmental 
Protection Agency and the National Oceanic and Atmospheric 
Administration (NOAA). The "black water" contained a high abundance 
of toxic and non-toxic microscopic plants.

Chuanmin Hu and other colleagues at the Institute for Marine Remote 
Sensing of the University of South Florida (USF), St. Petersburg, 
Fla., and colleagues from the Florida Fish and Wildlife Conservation 
Commission (FFWCC) and the University of Georgia, co-authored an 
article on this phenomenon that appeared as the cover story of a 
recent issue of the American Geophysical Union's Geophysical Research 
Letters.

"The water appeared black in satellite imagery because the 
concentration of the microscopic plants and other dissolved matters 
were high," Hu said. Because plants and dissolved matter absorb 
sunlight, they reduce the amount of light normally reflected from the 
ocean.
When a red-tide bloom occurs the water takes on various hues of red 
or brown. While not all microscopic plants contribute to red tides, 
the darker hue created by both the plankton and the harmful algal 
blooms made the water appear black when seen from the satellite.

When Hu and his colleagues examined the data collected by divers from 
the dark water area in the Florida Keys, they discovered a 70 percent 
decrease in stony coral cover, a 40 percent reduction of coral 
species, and a near-elimination of sponge colonies at two reef sites 
after the dark water passed. By examining satellite images and field 
survey data, the authors concluded that the coral reef ecosystem was 
stressed by microscopic organisms and toxins contained in the dark 
water.

The "black water" event caused alarm among local fishermen, divers, 
and the public, as the color of the water was unusual and fish seemed 
to avoid this large area of dark water. Satellite instruments such as 
the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) aboard Orbimage's 
SeaStar satellite and the Moderate Resolution Imaging 
Spectroradiometer (MODIS) aboard NASA's Terra and Aqua satellites 
provide information on ocean color that allows scientists to monitor 
the health of the water and the shallow benthic (ocean bottom) 
environment. The SeaWiFS and MODIS measurements of the dark water led 
to a number of investigations to help clarify the issues and to 
provide answers to the public's concerns.

During January 2002, SeaWiFS detected the dark-colored water in the 
Florida Bight, just southwest of the Everglades. In fall 2001, the 
SeaWiFS images showed an extensive red tide off Florida's central 
west coast, near Charlotte Harbor.

Red tides occur every year off Florida and are known to cause fish 
kills, coral stress and mortality, and skin and respiratory problems 
in humans. They are caused by high concentration of microscopic 
plants called dinoflagellates. Other microorganisms called 
cyanobacteria can also cause harmful algal blooms. The waters 
containing this red tide migrated to the south along the coast.

Winter storms caused large amounts of fresh water to drain from the 
Everglades into Florida Bight (the curve in the shoreline from the 
Keys north to Everglades National Park on the mainland), carrying 
high levels of nutrients such as silicate, phosphorus, and nitrogen 
to the sea. These caused a bloom of the microscopic marine plants 
known as diatoms in the same patch. The bloom turned the water dark 
and the "black water" patch re-circulated for several months in a 
slow clockwise motion off southwest Florida in the Florida Bight. 
Slowly, the dark water drifted farther south and toward the Florida 
Keys. By May 2002, the "black water" had moved through passages in 
the Florida Keys, dispersing into the Atlantic and the Gulf Stream.

Co-authors on this research article included Serge Andrefouet and 
Frank E. Muller-Karger of USF; Keith E. Hackett, Michael K. Callahan, 
and Jennifer L. Wheaton of FFWCC, St. Petersburg, Fla.; and James W. 
Porter of the University of Georgia, Athens, Ga.

NASA funded part of this research as part of its Earth Science 
mission to understand and protect our home planet. NASA's Earth 
Science Enterprise is dedicated to understanding the Earth as an 
integrated system and applying Earth System Science to improve 
prediction of climate, weather, and natural hazards using the unique 
vantage point of space.

For more information and images, see:
http://www.gsfc.nasa.gov/topstory/2003/0423blackwater.html

More on SeaWiFS can be found on the SeaWiFS website:
http://seawifs.gsfc.nasa.gov/

Information on the MODIS instrument can be found at:
http://modis.gsfc.nasa.gov/

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