Harmful Algal blooms (HABs) are a global issue with economic, ecologic and biomedical implications. Shellfish mortalities associated with HABs have been observed. Algal toxins accumulate in some bivalves whereas other species won't display similar accumulation. Furthermore, one species may respond differentially to various toxins, which causes difficulties to generalize the mechanisms involved. Only very few studies investigated cellular and molecular mechanisms occurring during HAB exposure. Exposure of bivalves to HABs may induce an inflammatory response involving hemocytes and oxidative activity. The need to understand cellular and molecular mechanisms during the response of bivalves to HABs appears necessary. At the cellular level, hemocytes may play primordial role. At the molecular level, oxidative stresses might be of extreme importance. The objectives of this project are to characterise the cellular and molecular inflammatory responses and oxidative activities of oysters to HAB exposure, and the potential involvement of hemocytes in transportation of toxin. In vivo exposures and oysters collected in situ during algal blooms will allow the evaluation of inflammatory response, oxidative and anti-oxidant activities, and localisation of algal toxins in the tissues. In vitro experiments will help to assess the interactions between hemocytes and algal cells, and cellular and molecular mechanisms directing the response, as well as the capacity of hemocytes to acquire and depurate the algal toxins. Gathering in vitro and in vivo / in situ results will provide understanding of the cellular and molecular events taking place during bivalve exposure to HABs. Such knowledge will help determine which are the key phenomena leading to toxin accumulation or detoxification. This research will allow to further investigate how the physiological state of bivalves can influence toxin accumulation, and will provide information for shellfish aquaculture, restoration and management.