The project of a national sea park in the Iroise reveals the difficulties of the islander (the inhabitants of Molène) to accept a foreign intervention on their land and sea territory. This article analyses the double relationship with the territory (resulting from a new management of the natural spaces) : on the one hand, the appropriation of space by a community, on the other hand, the will to transmit it to future generations, like a heritage. The opposition between islanders and mainland managers is due to the fact that the latter consider natural and threatened a space that the former managed themselves since long.