In this second part, discover the biodiversity of the oceans, from the coral reefs to the coastal lagoons. This biodiversity, of which the knowledge is still partial, is the subject of great attentions, by virtue of its importance in the main balances of the biosphere, but also by virtue of the favors it does for the human societies, beginning with the supplying of food resources. The ecosystem approach to fisheries is currently developed in this context, in order to reconcile those different preservation issues.