The west coast consists of a wide coastal plain, with numerous rivers, and also a wider continental shelf. This coast is swept by the northward flowing currents of the Mozambique Gyre and is further affected by large tidal ranges. Reef development is extensive in both the northern and southern parts of this coast. The southernmost reefs are offshore around Banc de l’Etoile and Nosy Manitsa. There are extensive fringing reefs along much of the coast north of Androka as far as Cap St. Vincent, varying between 500 meters and a few kilometers offshore, and separated from the shore by a generally shallow channel. Around Tulear a more complex system of offshore reefs is present, with shoreline fringing communities, a series of inner lagoon reefs, and a well developed barrier reef – the Grand Récif – which runs continuously for 18 kilometers. Between the Bay of Assassins and Morombe a sequence of reefs, many with associated sand cays, has developed offshore, forming a fragmented barrier reef system. This same barrier system reappears north of the Mangoky Delta with a series of submerged banks and emergent reefs with sand cays. Along most of the central section of the west coast there is no reef development, probably due to the terrigenous sediments discharged from rivers. Offshore, however, there are reefs towards the edge of the continental shelf associated with the Barren Islands and the Banc Pracel, although these remain poorly documented. In the northeast, fringing reefs reappear along the coast and the offshore islands, notably Nosy Bé and the Mitsio and Radama Archipelagos, although their distribution is discontinuous around the many rivers and bays. On the outer edge of the continental shelf in the far north, there is another series of raised banks, actually forming a near continuous ridge which may be the remains of a large barrier reef system. Coral cover is reported to be very high along the outer slopes, heavily dominated by formations of the sheet coral Pachyseris speciosa.