EN
Each population studied employs a personal strategy to ensure its successful occupation of and reproduction in a very harsh Mediterranean ecosystem, the Mauguio lagoon (Gulf of Lions). P. minutus undertakes relocation to search for quality biotopes and to ensure success in the various stages of its life cycle by genesic migration (for reproduction) to the sea of adults for spawning, and by postlarval trophic immigration within the lagoon. However, P. microps, more euryvalent, is completely sedentary. Although G. niger has adaptive capacities potentially similar to those of P. microps, and makes a considerable reproductive effort, this species is subject to relative demographic failure, mainly owing to the scarcity of nesting areas both in the lagoon and at sea. The spatial and trophic co-exploitation of the lagoon is facilitated for these three populations by the migrational behaviour of P. minutus, the different static and dynamic characteristics of each species studied, and the evolution of the seasonal vegetation in this environment.