A multispecies dynamic simulation model (ERSEM) was used to examine the influence of allelopathic and trophic interactions causing feeding avoidance by predators, on the formation of harmful algal blooms, under environmental scenarios typical of a Mediterranean harbour (Barcelona). The biological state variables of the model included four functional groups of phytoplankton (diatoms, toxic and non-toxic flagellates and picophytoplankton), heterotrophic flagellates, micro- and mesozooplankton and bacteria. The physical–chemical forcing (irradiance, temperature and major nutrient concentrations) was based on an actual series of measurements taken along a year cycle in the Barcelona harbour. In order to evaluate potential effects of advection, some runs were repeated after introducing a biomass loss term. Numerical simulations showed that allelopathic effects of a toxic alga on a non-toxic but otherwise similar competitor did not have appreciable influence on the dynamics of the system. However, induction of avoidance of the toxic alga by predators, which resulted on increased predation pressure on other algal groups had a significant effect on the development of algal and predator populations. The presence of advection overrided the effect of these interactions and only allowed organisms with sufficiently high potential growth rates to thrive

We acknowledge the support from the European Commissions Environment and Sustainable Development (ESD, FP-V, Research into the Development of Sustainable Marine Ecosystems, Key Action 3) under contract EVK3-CT-1999- 00015 for BIOHAB (Biological control of Harmful Algal Blooms in European coastal waters). We are specially grateful to P. Ruardij for providing the ERSEM code and for his valuable help about the use of ERSEM model

Special issue Workshop on Future Directions in Modelling Physical-Biological Interactions (WKFDPBI).-- 15 pages, 14 figures

Peer reviewed