The sea of the Cinque Terre is a very particular sea and coast. With the exception of two long sandy stretches near Monterosso and of other, mainly cobble or stone, beaches, the coast plunges steeply into the sea with almost vertical cliffs, which continue underwater. The Cinque Terre's seabed is thus very deep and is one of the richest of the whole of Liguria in terms of wildlife. "Punta Mesco" is the North-East limit of the Cinque Terre Marine Reserve and is surrounded by a deep seabed and by steep underwater rock sides, near which live pelagic species like the maigre and the dentex, as well as permanent species like the white bream, black umbra and grouper.

The rocky substrata also hosts colonies of multicoloured "Paramunicee" and, in the darkest caves, red coral. From Punta Mesco to Monterosso the seabed is not particularly deep. It is shallow to begin with, at the foot of Monterosso, spreading out as a long sandy stretch going out at sea offering the ideal substrata for the "Posedonia Oceanica" sea grass, a real 'lung' for the marine ecosystem, which is getting more and more scarce due to fishing by dragging nets along the seabed. Monterosso's sea prairie is today included inside the Cinque Terre's Marine Reserve and is thus protected. Having roots, stem and leaves, the posidonia seagrass is a superior plant, an important biologic indicator of polluting agents. Furthermore, it consolidates the substrata where it lives, making up actual praries, which help limit the damage made by rough sea and currents against the coast.