Evaluation of the use of SeaWiFS imagery for detecting Karenia brevis harmful algal blooms in the eastern Gulf of Mexico

Abstract

Frequent blooms of the toxic dinoflagellate, Karenia brevis, along the west coast of Florida are of considerable concern to state resource managers due to numerous ecological and health impacts. With the availability of remotely sensed ocean color imagery from SeaWiFS, a regional algorithm that compensates for the scattering of sediments in coastal waters can be applied to accurately estimate chlorophyll concentrations in coastal areas of Florida. Chlorophyll anomalies of 1 μg l −1 based on a 60-day running mean are currently used along the Panhandle and west Florida coast, to detect K. brevis blooms exceeding 100,000 cells l −1. This is the first step in an early warning system to forecast K. brevis blooms in the eastern Gulf of Mexico. A retrospective analysis was performed on imagery acquired from 1999, 2000 and 2001 to determine the accuracy of this technique in detecting K. brevis blooms in this region. During the K. brevis bloom season from August through April, chlorophyll anomalies accurately identified K. brevis blooms along the Florida Panhandle, from Tampa Bay to Cape Romano and Key West >83% of the time. Frequent chlorophyll anomalies were falsely observed in the spring and early summer, prior to the beginning of the K. brevis bloom season. Areas rich in colored dissolved and particulate matter were prone to anomalies that falsely identify K. brevis blooms; however, blooms rarely originate in these areas.