22 - Coral Reefs and Reef Islands of the Amirantes Archipelago, Western Indian Ocean

Abstract

A series of habitat maps derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data of the reefs and reef islands of the Amirantes archipelago, Seychelles, western Indian Ocean, are presented. Broad-scale coral reef structures and geomorphic units are described, along with a range of habitats associated with lagoons, reef-flats, and sand cays. Five different geomorphic units are outlined, comprising three different types of platform reefs, atolls, and submerged atolls. Biological assessments of benthic character in this chapter are supported by over 1,500 ground reference records of the terrestrial and marine environments. Further detail on production of the habitat maps and individual island descriptions can be found in the Atlas of the Amirantes. The chapter presents the results of a collaborative expedition between the Cambridge Coastal Research Unit and Khaled bin Sultan Living Oceans Foundation in January 2005. Airborne remote sensing Compact Airborne Spectrographic Imager (CASI-2) imagery was acquired over the Amirantes Bank from which both the geomorphic and biological character of the 13 reef islands could be examined. The spatial distribution of habitat types by island location shows that islands on the western margin of the Amirantes Bank are characterized by a restricted range of terrestrial and littoral habitats, whereas those on the eastern side of the Bank show a greater range of habitats, particularly in subaerial environments. This may be because of their greater exposure to incident waves driven by the southeast Trade Winds, which encourage reef growth and subsequent island formation.