A numerical analysis of landfall of the 1979 red tide of Karenia brevis along the west coast of Florida

Abstract

A simple ecological model, coupled to a primitive equation circulation model, is able to replicate the observed alongshore transport of the toxic dinoflagellate Karenia brevis on the West Florida shelf during a fall red tide in 1979. Initial land fall of these populations at the coast in our model matches shoreline data sets as well. The simulated vertical movement of K. brevis, in response to light-cued migration and nocturnal mixing, also mimics these aspects of the next fall red tide in 1980, suggesting that sunrise populations may provide the strongest surface signal, for detection of red tides by remote sensors aboard aircraft and satellites. Once a mature red tide is formed, a light-regulated maximal growth rate of 0.15 day −1, reflecting nutrient-limitation, and no other loss processes may be an adequate description of population dynamics above the 30–40 m isobaths, where blooms of K. brevis originate. Within shallow waters at the 10-m isobath, however, an apparent larger growth rate of 0.80 day −1—as a presumed consequence of frontal aggregations—must be offset by unknown processes of algal mortality. Likely candidates for cumulative, biomass-dependent losses are UV-B irradiation, microbial-induced lysis, and unselective grazing pressure from copepods, protozoans and heterotrophic dinoflagellates.