A hydrobiological model as a tool for the detection of hab episodes Application to Thermaikos gulf

Abstract

Algal blooms constitute one of the most important en-vironmental phenomena in coastal areas; particularly if these blooms contain potential toxic algae populations. As Dinophysis spp. had been recorded in low population densities, all over the year in Thermaikos Gulf, a mathematical model was developed to simulate critical conditions for the appearance of an algal bloom episode and the population's dispersion in space and time. The model is constituted from two parts, a mechanical which computes the hydrodynamics and the matter transfer of the investigated area as well as a biological part which computes the cells growth rate and the cells decay. The application of the model simulations were based on: (a) different starting population densities, (b) different positions in the Gulf as sources of initial population, (c) different wind direction and speed. The results show that population densities above a number of 500-1000 cells/L with mean wind speed of 5 m/ sec and low grazing rates may regulate the appearance of a HAB in Thermaikos Gulf. The dispersion of algae population was finally found to be regulated by wind velocity, filter feeder's abundance. It was found that if an episode starts in the inner part of the Gulf, under the influence of the prevailing north and south winds over the area of the Gulf, the population hardly reaches to the outer part of the Gulf, while an episode in the outer area of the Gulf leads to a variety of pattern dispersions depending on the different wind conditions.