Some dynamic models show excitable behavior, meaning that the system is capable to develop a large response to certain perturbations. In this context, algal blooms can be interpreted as instabilities of the system, associated with the attainment of a critical value of the net growth rate of the blooming species. In this communication, we consider a simple model with two microalgal species and one zooplankton grazer, and analyze how a reduced grazing pressure can allow an algal species with some defense mechanism (the >toxic> species) and a lower intrinsic growth rate than a competitor, to proliferate and become dominant. First, we derive general relationships between phytoplankton growth and zooplankton grazing. Next, these relationships are applied to two common grazing response functions, to deduce the mathematical constraints that the parameters of these functions must obey in order to allow the proliferation of the >toxic> species. To assess the usefulness of the deduced relationships in a more general framework, the results are applied in the context of a multispecies ecosystem model

17th International Conference on Harmful Algae (ICHA), 9-14 October 2016, Florianópolis, Santa Catarina, Brazil.-- 1 page

Peer Reviewed