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Résumé de la communication de Charles LE PABIC (Museum National d'Histoire Naturelle, Paris) donnée à l’occasion du séminaire Les constructions en milieu marin / Constructions in marine environment du 14 au 19 mars 2016In the course of evolution, many aquatic organisms developed different ways to control their buoyancy, i.e. to maintain their body at the same depth or to change of depth. In fact, organisms had to "understand" physics and "adapt" to regulate their buoyancy. The Archimede's principal, describes and explains how the buoyant force counterbalanced the weight. Two other laws important to consider buoyancy regulation are: the PAscal's law and the Boyle's law. They stated respectively that, in water, the pressure (called hydrostatic pressure) increases with depth; and that the gas volume in a closed system decreases with the increase of the pressure.Marine organisms control their buoyancy in order 1) to save energy allocated in vertical swimming, 2) to avoid troubles linked with quick pressure variation as well as 3) to stay in an appropriate living environment. Some marine organisms like jellyfish or sharks regulate their body density close to the one of the seawater, and thus spend less energy to maintain their body at a desired depth. Other organisms are able to adjust their buoyancy depending on their life cycle. Crustacean, like copepodsaccumulate fat during winter to be neutrally buoyant at a depth of 120 m where the predation is limited. The female's sea turtle Caretta caretta are also known to select their depth residence during apnea function of their lung volume in order to save energy during eggs maturation period. Pelagic squids accumulate in their body an ammonium-enriched fluid of low density, which allow them to be neutrally buoyant. Finally, other organisms developed elaborated system allowing them to change their buoyancy within a short period of time. One of the most known example is the fish swim bladder, an inner gas-filled cavity that can be filled or emptied as a function of their vertical movements. The sperm whale possesses an organ filled with ester oil, called spermaceti organ, which change of density function of temperature. This elaborated organ facilitates the vertical movements of the sperm whale during its deep dives. Finally, the shelled mollusk cephalopods of the Nautilidae, Spirulidae and Sepiidae families present the particularity of using their aragonitic shells to regulate their buoyancy. Indeed, their shells are made of hollow chambers, which can be filled with various volume of gas and therefore change the animal density. The inner Sepiidae shells are the most complex structures gathered together high compressive strength, high porosity and high permeability. Moreover, its inner microstructure seems also dedicated to the fluids (i.e. gas and liquid) repartition. Our current research on such elaborated structures could be of interest for the future of building in marine environment.Summary