Observing Red Tide Algal Blooms From Satellite Ocean Color Imagery: West Florida Shelf

Harmful algal blooms (HABs) from Karenia brevis occur along the west Florida shelf (WFS) almost every year, producing a brevetoxin that is harmful to birds, fish, marine mammals, shellfish, and humans. These HABs are commonly known as "red tide" from the reddish discoloration in the water, but color can vary from yellow to deep brown depending on other parameters. Ocean color data is a viable tool for monitoring the outbreak and persistence of these ecological phenomena. Also, the spatial extend of this outbreak could be evaluated effectively from satellite imagery. Chlorophyll (Chl) and sea surface temperature (SST) data from four satellites during the period from 2010 to 2013 were analyzed, and compared the monthly composite data with in situ observation on K. brevis cell counts collected by the Florida Fish and Wildlife Conservation Commission (FWC). Remote sensing data were extracted from the NASA Ocean Color data servers and were processed using WimSoft, a Windows-based remote sensing data analysis program. Based on the comparison of data from 26 transects from the WFS, which were extended from nearshore to 400 km offshore, highest Chl concentrations were observed in the sector from St. Petersburg to Sanibel Island. FWC data also showed that highest K. brevis cell counts were concentrated in this region during the 2011 to 2012 period. Additionally, a high Chl concentration was observed for the Big Bend region, particularly during the spring and early summer. The inter-annual variability of Chl, SST, and red tide occurrence are also discussed in this study.