Does Overfishing Exacerbate Florida's Red Tide Effects? A Trophodynamic Approach to Study How the West Florida Shelf Ecosystem Responds to Harmful Algal Bloom Events

Karenia brevis dinoflagellate blooms off the west coast of Florida can create devastating effects on coastal communities when they release an ichthyotoxin, known as a brevetoxin, as the fragile cells lyse. At high densities, harmful algal blooms of these cells can strand hundreds of fish along the beaches and necessitate closure of shellfish fisheries. Their impact on Florida’s fisheries, however, is not clearly understood due to limited knowledge of the relationship between K. brevis cell counts and fish mortality. To fill this gap and study ecosystem responses to K. brevis blooms, Ecopath with Ecosim modeling is used to simulate K. brevis bloom events on the coastal ecosystem assuming three possible relationships between cell count and fish mortality – linear, exponential, and step-function. The model can demonstrate possible bottom-up and top-down effects on the food web imposed by K. brevis blooms, that periodic bloom perturbations shape the community structure of the West Florida Shelf, and finally that overfishing exacerbates the severity of these bloom effects. A West Florida Shelf model is used to test these hypotheses to understand the dynamics that exist within that ecosystem, and contribute to the understanding of the extent to which the ecosystem can be safely exploited.