We will focus on a crucial step of the bivalves’ life cycle : the settlement and metamorphosis, which ensures larval recruitment and renewal of populations. However, ocean acidification (OA) or the continuous release of pharmaceutical residuals (PR) in the coastal environment can mortgage the pelago-benthic transition by perturbating neurotransmission systems, behaviours and sensorial capacities of exposed animals. These factors co-exist in the natural environment and yet, a few number of studies focused on their interaction. The objectives of the project are : 1) in a normal environmental condition, to highlight the neuroactive compounds of settlement and metamorphosis in the Pacific oyster, Crassostrea gigas, larvae ; and 2) to evaluate the interactive effects of OA x PR on the neuro-physiological, behavioural (swimming) and sensorial (facing a predation risk) responses of C. gigas larvae. The larvae will be exposed, from embryo to metamorphosis, to different conditions: current value of pH (~ 8.1) or projected value in 2100 (pH -0.4 units), and environmentally-relevant concentrations of oxazepam, anxiolytic PR frequently detected in coastal waters. This innovative project supports a multi-stress approach and targets biological responses which are largely understudied in bivalves.