NOAA Suspects River Nutrients Initiate Florida Red Tides
A new National Oceanic and Atmospheric Administration (NOAA)
research model indicates nutrients flowing from the Mississippi River
may stimulate harmful algal blooms to grow on the continental shelf off
the west coast of Florida.
The peer-reviewed hypothesis is being published in a special issue on Florida red tide in the journal Continental Shelf Research.
According to the model, algal blooms form on the Florida coast
because of weather and gulf currents. The algae grows offshore,
supplied with additional nutrients that appear to have originated from
the Mississippi River, in a process driven by normal seasonal wind
"We found that the concentrations of nutrients needed to start the
Florida red tides is much lower than previously suspected," said NOAA
oceanographer and lead author of the paper, Richard Stumpf, Ph.D. "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."
Harmful algal blooms occur in the waters of almost every U.S.
coastal state, caused by numerous different species. Their direct
economic effects in the United States are estimated to average $75
million annually, including public health costs, commercial fishing
closures, recreation and tourism losses, and in management and
While outflow from the Mississippi River travels westward most of
the year, early summer prevailing winds carry it eastward, bringing
nutrients, especially nitrogen, toward Florida. The nutrients then
settle into deeper water, where they are taken up by the algae. The
blooms, of the red tide species Karenia brevis, start on the
shelf and are brought onshore and concentrated by the prevailing wind
patterns of late summer and fall. The study has implications for
predictions and for monitoring of these blooms, including potential
variations in intensity between years and regions. The findings also
indicate that even relatively small increases in nitrogen can account
for the initiation of the blooms offshore.
NOAA, working in partnership with scientists at Mote Marine
Laboratory in Sarasota, Fla., already is beginning to test the
hypothesis through the use of autonomous underwater vehicles carrying
instruments called "BreveBusters." The vehicles are checking for the
presence of Karenia brevis blooms further off the coast in deeper Gulf of Mexico waters.
The new hypothesis links results from several extensive research
programs conducted in the Gulf of Mexico over the last decade including
the NOAA-funded Florida Ecology and Oceanography of Harmful Algal Bloom
program. Understanding initiation of red tide should lead to improved
monitoring, modeling and research strategies for these blooms.