Black water turns the tide on Florida coral (Forwarded)
Andrew Yee
Goddard Space Flightt Center, Greenbelt, Md. April 17, 2003
Rgu...@pop900.gsfc.nasa.gov
(Phone: 301/286-4044)
Pam Bellis
University of South Florida
bell...@aol.com
(Phone: 727-553-1297)
Allison McDonald
Florida Fish and Wildlife Conservation Commission
Allison....@fwc.state.fl.us
(Phone: 850-488-4676)
Kim Carlisle
University of Georgia
kosb...@uga.edu
(Phone: 706-583-0913)
Kent Laborde
NOAA
kent.l...@noaa.gov
(Phone: 202-483-5757)
Harvey Leifert
American Geophysical Union Tel.
hlei...@agu.org
(Phone: 202-777-7507)
RELEASE NO: 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/
--
Andrew Yee
ay...@nova.astro.utoronto.ca