Abstract Several field data and experiments show that zooplankton may react to the presence of toxic phytoplankton by reducing its consumption up to the point of starvation. We propose a mathematical system to model this situation using a Monod–Haldane response function. Our results indicate that this mechanism ensures that the toxic phytoplankton does not drive the zooplankton population towards extinction. Also, the insurgence of brown tides is shown numerically under the assumptions underlying this model.