Blooms of the toxic dinoflagellate Gymnodinium catenatum are a recurrent phenomenon in the Iberian upwelling system albeit highly variable at the decadal, annual and event scales. In this area the bloom dynamics of G. catenatum is usually interpreted as being more dependent on constraints in the planktonic stage than on the build-up of a benthic seed population. This hypothesis is based both in field and laboratory results. But, the question remains, where does the seeding inoculum come from? This project looks at this question by investigating the physical and biological processes that determine G. catenatum bloom initiation, with emphasis on benthic resting stages (cysts). Other harmful and potentially harmful (HABs) cyst producing species will also be investigated.