The nature reserve and the Natura 2000 site encompass all habitats that characterise a bay: sand, roselières, mudflats and salt water marshes just as dunes and cliffs. The vast intertidal zone, which is covered and uncovered in the course of the tides, allows for a development of plankton influencing the operation of the whole of the vast bay of Saint-Brieuc. The ground of the bay of Saint-Brieuc represents a humid littoral zone of international interest for the reception of migratory avifauna.
Every winter, from October to March, the bay becomes the scene of an exceptional spectacle. For, attracted by mild temperatures and abundant food, about 40 000 birds gather in the bay. Among them, many migratory birds have travelled up to 10 000 kilometres to reach our coast. In the middle of winter there have been countings of up to 90 bird species. In spring and summer the winter guests hand the place over to the migratory birds passing through, who only make a short stay of some days to gather strength before travelling on. Other birds stay all year long or are present only for the midsummer period and breed in the surrounding area.