"Ocean pH has already declined by 0.1 units since pre-industrial times and is predicted to further decline by another 0.3 units by the end of the century as a consequence of increasing anthropogenic CO2. Reef-building corals and calcifying cold-water communities such as pteropods (molluscs), were identified as at higher risk. This project will focus on the effect of rising pCO2 on two sensitive and complementary models: Acropora millepora coral larvae and Limacina helicina pteropod. Both construct aragonitic skeleton/shell, a crystalline calcium carbonate polymorph which is less stable than calcite and dissolve more easily under higher pCO2. Because of their crucial ecological and economical roles, it is pivotal to understand and quantify the response of these organisms to rising pCO2 in more detail. The first part of the project will concern effect of rising pCO2 on calcification both in coral larvae and in pteropods. The second part of the project will concern the effect of rising pCO2 on symbiont acquisition of coral larvae. Indeed, most reef-building corals develop an endosymbiotic relationship with photosynthetic dinoflagellates, Symbiodinium sp., commonly called zooxanthellae, which are known to influence coral calcification. Objectives will be investigated by complementary physiological and molecular approaches. The molecular approaches, consisting in large oligoarray analysis and 454 sequencing, will allow the identification of complete molecular pathways involved in rising pCO2 response in both organisms. Together, all the expected results will contribute to improve our knowledge on the essentials processes of 1) calcification both in Cnidarians and Pteropods, and of 2) symbiosis in Cnidarians."