Coastal Services Center

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Monitoring Harmful Algae

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Sampling miles of shoreline for harmful algal blooms can be more efficient when information is available to identify potentially affected areas. Phytoplankton concentrations at the surface of the water column can be seen using SeaWiFS (Sea-viewing Wide-Field-of-View Sensor) chlorophyll imagery. Areas near vulnerable shellfish habitats that have high chlorophyll or show changing conditions can be closely monitored.

The Project: Monitoring for Red Tide on Florida's Southwest Coast

States are responsible for monitoring water quality to manage shellfish harvesting areas that must be closed when harmful algae or other pollutants are present. Karenia brevis, a harmful species of phytoplankton responsible for red tides, is frequently found in the late summer and fall in the Gulf of Mexico. Consumption of shellfish contaminated by red tide causes neurotoxic shellfish poisoning in humans. To ensure safe seafood, the Florida Division of Aquaculture and the Florida Marine Research Institute work together to test shellfish harvesting areas for the presence of red tide and to regulate harvesting.

Florida has hundreds of miles of coastline that is suitable habitat for shellfish. To efficiently allocate resources needed to monitor water quality, managers use the chlorophyll concentrations provided by SeaWiFS imagery to target sampling efforts. This imagery is provided to state and local managers in Florida by a cooperative effort between the NOAA National Ocean Service and CoastWatch programs. The information, including the interpreted image, the last-known position of the red tide bloom, and the speed and direction of local winds, is e-mailed to managers. They can then use this bulletin to direct crews to the appropriate areas to take water samples. Only analyses of the water sample by microscope will determine whether red tide is present; the chlorophyll imagery is not sufficient to distinguish harmful from non-harmful algae.

An excerpt from a bulletin that includes a SeaWiFS image. In the image violet and blue represent the lowest chlorophyll concentrations, green and yellow are intermediate, and red is high. For more information about the bulletin visit the HAB Forecasting Web site.

Deriving Phytoplankton Data from SeaWiFS Imagery

SeaWiFS collects radiances (light intensities) that are sensitive to subtle variations in the color of the ocean. Algorithms are applied to the data to discriminate between chlorophyll, phytoplankton, and other substances in the water. Since spatial resolution is low (one kilometer) the data are most reliable for offshore coastal areas and must be used cautiously in bays and estuaries.

The Result

Since 2000, SeaWiFS imagery has been used by state, county, and municipal managers to help direct sampling efforts in Florida. The information provided by SeaWiFS imagery is only a part of the information used to decide when and where to sample for harmful algae. Since red tide species cannot be discriminated from other species in the image, water samples must still be taken to verify red tide. Despite these limitations, SeaWiFS has proven an effective tool to more efficiently monitor this regional problem.

For More Information

• Florida Marine Research Institute
• Florida Division of Aquaculture
• The Harmful Algae Page
• Center for Coastal Monitoring and Assessment HAB Projects
• Harmful Algal Bloom Bulletin

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