Ecologie et écophysiologie des espèces du genre Pseudo-nitzschia

Some species of Pseudo-nitzschia genus produce an amnesic neurotoxin called domoic acid (DA). After been bioaccumulated in marine trophic webs, this toxin is responsible of amnesic shellfish poisonning (ASP) in humans. ASP events are responsible of severe sanitary and socio-economic troubles. Several toxic blooms were observed in the Bay of Seine since 2004 causing closures of scallop fishery. The aim of this PhD was to study the ecology and ecophysiology of Pseudo-nitzschia species, which are potentially responsible of ASP events in the Bay of Seine. To study the bloom dynamics of present Pseudo-nitzschia species in the Bay of Seine, an insitu study was performed off the coast of Luc-sur-Mer throughout two years (2012-2013). In addition to natural population studies, laboratory studies were conducted on the ecophysiology and the life cycle of Pseudonitzschia species. The influence of temperature and irradiance was studied on P. Australis physiology and toxicity and on P. Pungens and P. Fraudulenta sexual reproduction induction. This work improves the understanding of the environmental drivers of Pseudo-nitzschia blooms in the Bay of Seine and our knowledge on the physiology and the life cycle of these species. Results underline the importance of specific diversity in the Pseudo-nitzschia genus both from ecological and physiological point of view.