ABSTRACT
The 13 atolls in the Western Indian Ocean described in this chapter include those in the Amirante Islands, the Aldabra Islands (both part of the Seychelles group), and the Iles Eparses in the Mozambique Channel. The Amirante atolls develop submerged rims, whereas most of the Aldabra group are raised slightly above sea level and are open. Three atolls are found in the Mozambique Channel and develop either submerged or open rims. Winds are monsoonal, from the northwest or southeast, but waves are most commonly from the southeast. Tidal range increases from 1.8 m in Seychelles in the north up to 3.0 m to the south and west. The dominant features of circulation in these areas include the South Equatorial Current (SEC) which occurs as a broad westward flow where the southeasterly trade winds occur year-round. The SEC flows around the northern tip of Madagascar and bifurcates forming eddies along the African coast with the Mozambique Current as it flows south into the Mozambique Channel and its atolls. However, during the austral summer, the southeasterly trade winds turn into westerlies. This shift causes a current reversal near the equator that generates an eastward-flowing South Equatorial Countercurrent that washes through the Seychelles atolls to the north.
Atolls in the western Indian Ocean include those in the Amirante Islands, the Aldabra Islands (both parts of the Seychelles group), and the Iles Eparses in the Mozambique Channel. These areas range from about 5°S to 22°S. Their biology, history, and other characteristics are described separately below.
