As soon as he crosses the mirror of the water, the man is amazed by the magnificent spectacle which offers to him in the deep of the Mediterranean Sea: meadows of sea grass, boulders colonized by a large variety of organisms, shoals of fish...

The layman may get easily impressed by this extraordinary variety of forms and colors, but he sees only the biggest and the most mobile forms. Nevertheless, some "keys species" of this ecosystem remain sometimes totally ignored. Who eats who ? How live and interact these strange organisms?