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Harmful Algae

Late every summer along the Florida Gulf coast, state managers anticipate the arrival of a red tide. The organism that causes red tide, a microscopic alga called Karenia brevis, produces a toxin that has many hazards. The toxin makes shellfish dangerous to eat. It causes fish kills, has been found to kill dolphins and manatees, and can make the air difficult to breath. Trying to monitor the 600 miles of coast from Pensacola to Key West is a daunting task. Methods for detecting and forecasting the location of the blooms of Karenia brevis will greatly aid the state in this monitoring effort. NCCOS is attempting to do that using sophisticated satellites and instruments.

The blooms typically start between August and October. While called red tides, they are rarely red, and can be brown, yellow or greenish, depending on the density and the other algae in the water. Simply looking for red water will not help, and red water can be caused by other factors, such as tannins from rivers, harmless algae, and sediment. So, scientists prefer to call these events “harmful algal blooms” or HABs (pronounced ‘habs’) rather than red tides.

Starting in August, NCCOS and Florida scientists begin communicating. Florida starts sampling in areas where the toxic algae most often comes ashore. NCCOS starts monitoring for blooms using satellite imagery of ocean color obtained through the NOAA CoastWatch program. The imagery can be obtained every 1-2 days. With sophisticated algorithms algal blooms can be found by determining the amount of chlorophyll in the water, and blooms are analyzed to assess whether they may be HABs. The HABs are more likely to appear when winds originate from the east or northeast, so winds and long-term marine forecasts are included in the analysis.

Once a HAB is identified, the imagery is used to determine the extent and strength of the bloom. This information is provided to the states as a bulletin so that they can best direct sampling. Forecasts of transport are made by analyzing the wind measured at NOAA buoys and comparing the results to the satellite and field observations. If a bloom is predicted to move westward, warnings are provided to officials in the states to the west, Alabama, Mississippi and Louisiana.

These bulletins continue during the bloom season, which often lasts through the winter in southwest Florida. Advisories are made throughout this time, as the blooms often start further north and move south through the season.

Efforts are being made to improve the accuracy of the detection and prediction methods, as well as automating much of the analysis. While we may not be able to stop the “red tides”, this monitoring effort may reduce the impact of the blooms and cost of monitoring for them.

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