Detecting Karenia brevis blooms and algal resuspension in the western Gulf of Mexico with satellite ocean color imagery Timothy T. Wynne a, * , Richard P. Stumpf a , Michelle C. Tomlinson a , Varis Ransibrahmanakul a , Tracy A. Villareal b a NOAA, National Ocean Service, Center for Coastal Monitoring and Assessment, 1305 East West Highway, Silver Spring, MD 20910, USA b Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA Received 22 September 2004; received in revised form 2 February 2005; accepted 16 February 2005 Abstract Blooms of the toxic dinoflagellate, Karenia brevis, have had detrimental impacts on the coastal Gulf of Mexico for decades. Detection of Karenia brevis blooms uses an ecological approach based on anomalies derived from ocean color imagery. The same anomaly product used in Florida produces frequent false positives on the Texas coast. These failures occurred during wind- driven resuspension events. During these events resuspension of benthic algae significantly increases chlorophyll concentrations in the water, resulting in confusion with normal water column phytoplankton, such as Karenia. A method was developed to separate the resuspended chlorophyll from the water column chlorophyll, decreasing the false positives used with the detection method. # 2005 Elsevier B.V. All rights reserved. Keywords: Anomaly; Chlorophyll; Gulf of Mexico; Harmful Algal Bloom; Karenia brevis; Remote sensing; Resuspension; SeaWiFS; Texas 1. Background Karenia brevis blooms are the principal cause of Harmful Algal Blooms (HABs) in the Gulf of Mexico (Kusek et al., 1999). K. brevis blooms cause massive fish kills, marine mammal kills and respiratory irritation in humans (Baden et al., 1995), and are also known to cause Neurotoxic Shellfish Poisoning (NSP) in various types of shellfish, which is hazardous to humans. Because they have such toxic effects, K. brevis blooms have been widely studied within the Gulf of Mexico in order to improve detection and monitoring. Tester et al. (1998) reported that the eastern gulf (the west coast of Florida) had experienced K. brevis blooms 26 out of the previous 27 years, and there has been a bloom reported every year since 1998. Because of the frequency of blooms on the west Florida shelf there has been an extensive HAB monitoring program in place for years in that region. For western portions of the gulf (the Texas coastline), only three bloom events were reported from 1935 to 1986. However, from 1986 to the www.elsevier.com/locate/hal Harmful Algae 4 (2005) 992–1003 * Corresponding author. Tel.: +1 301 713 3028x139; fax: +1 301 713 4388. E-mail address: timothy.wynne@noaa.gov (T.T. Wynne). 1568-9883/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.hal.2005.02.004