Coordinated Observing and Modeling of the West Florida Shelf with Harmful Algal Bloom Application

The central portion of the west Florida continental shelf is the epicenter for blooms of the harmful alga Karenia brevis, which tends to form at mid-shelf under nutrient depleted, or oligotrophic, conditions. Whether or not the shelf is conducive to such bloom formation in any given year appears to be related to when and where the Gulf of Mexico Loop Current, a western boundary current, interacts with the shelf slope. If this occurs in the southwest corner, where shallow isobaths wrap around the Florida Keys at the Dry Tortugas, then the entire west Florida shelf may be set into a protracted upwelling circulation that can both reset water properties and transport mid-shelf materials to the shoreline within the bottom Ekman layer. The 2018 K. brevis bloom provides one such example, as described via a coordinated program of coastal ocean observing and modeling. Both the elevation of K. brevis cell counts along the coast and their eventual cessation may be largely accounted for by the coastal ocean circulation, as driven, in part, by the Loop Current’s interaction with the shelf slope.