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NCCOS Sponsored Research Advances Efforts to Understand Recent Florida Red Tide Events

Florida Red Tide Bloom of Karenia brevis

Florida Red Tide Bloom of Karenia brevis (Photo: WHOI) Below: “shellfish closing” photo caption (Photo courtesy of NOAA)

Karenia brevis, often called the “Florida Red Tide,” is a highly toxic alga that causes human respiratory distress, shellfish toxicity, animal mortalities, and water discoloration. K. brevis blooms throughout the Gulf of Mexico, and is occasionally transported to the Southeast U.S. coast. In U.S. waters, the blooms occur almost annually in the fall along the West Florida Shelf, and less frequently in other coastal areas, resulting in major impacts on human health, tourism, shellfish industries, and ecosystems, capturing the attention of the public and media.

In January, 2005, an unusually early and large bloom of K. brevis developed on the West Florida Shelf, leading to mass fish kills and reports of human respiratory irritation. In the early summer, the bloom receded to an area in southern Tampa Bay, but then a unique set of oceanographic conditions caused the bloom to expand offshore and become trapped near the bottom where mortalities of some fish and bottom-dwelling organisms resulted from contact with K. brevis toxins.

The decaying animals and K. brevis cells caused depletion of bottom water oxygen, which led to mass mortalities of diverse organisms across stretches of sea-bottom including coral reef environments.

Data collected by NCCOS-funded researchers and the State of Florida, with assistance from local divers, indicated that the impacts were widespread, affecting an area of over 2,162 miles 2 west of central Florida.  The last time wide spread bottom water anoxia occurred in the same area was 1972, according to Florida’s Fish and Wildlife Research Institute. Unusually high numbers of manatee, dolphin, and turtle deaths during the 2005 bloom have prompted the first ever declaration of a multiple species Unusual Mortality Event, triggering an intensive investigation under the Marine Mammal Protection Act.

Additional ECOHAB and MERHAB Advances in Florida

shellfish closing sign

  • Two atypical nutrient sources are hypothesized to fuel some K. brevis blooms: 1) nitrogen-fixing cyanobacteria stimulated by iron from wind-driven Africa dust and 2) aggregations of dead, decaying fish.
  • Faster, easier, and more economical methods for detection of K. brevis cells (e.g., BreveBuster) and its toxins (e.g., ELISA, an enzyme immunoassay) have made protecting public health and mitigating impacts more reliable and attainable.
  • A comprehensive monitoring program using a geographically broad citizen monitoring network, automated instrumentation, and biophysical forecasts was implemented.
  • Researchers discovered certain bacteria that co-occur with K. brevis can “attack“ and kill K. brevis cells, acting as natural control. Their application as a control tool still needs to be explored.
  • Researchers recently attempted to treat a K. brevis bloom with clay slurries for the first time in US open waters. This pilot study came after years of work that began with experiments in test tubes but expanded to real world application as our knowledge grew.

For more information on NCCOS’s HAB programs, please visit

NCCOS has invested more than $12 million since 1997 to help Gulf of Mexico coastal managers reduce public health risks and economic impacts of K. brevis through its support of the Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) and Monitoring and Event Response for Harmful Algal Blooms (MERHAB) programs.

One investment example is the NOAA- and EPA-funded “ECOHAB: Florida” project, which involved Florida state managers, academic institutions, local governments, and business organizations. “ECOHAB: Florida” researchers studied K. brevis bloom dynamics for five years, compiled one of the longest-running datasets (48 years) for HAB research and coastal ecosystems in general, and developed a complex model to tease out important environmental factors controlling blooms.

A MERHAB-funded monitoring network now employs this biophysical model for tracking and predicting Karenia blooms. NCCOS’s HAB programs continue to strive to advance scientific understanding and our ability to detect, predict, control, and mitigate HAB events.

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