A. B. Hagan

Coral reefs and reef islands of the Amirantes Archipelago, Western Indian Ocean

Publisher Summary 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.

Observations of dugongs at Aldabra Atoll, western Indian Ocean: lagoon habitat mapping and spatial analysis of sighting records

Until recently, it was thought that dugongs (Dugong dugon) were extinct in the Seychelles. However, a collection of sightings at Aldabra Atoll, a World Heritage Site in the Seychelles, has renewed interest in dugong distribution in the western Indian Ocean. This article consolidates the records of dugong sightings held in the Aldabra Research Station library and explores their spatial patterning. The locations of sightings (2001–2009) are plotted onto a high-resolution benthic habitat map of the Aldabra lagoon created by classifying a QuickBird satellite remote-sensing image in January 2009. A spatial cluster detection procedure is applied to point records of sightings to reveal a statistically significant cluster of sightings in the north-west of the lagoon, at Bras Monsieur Clairemont, suggesting a mutual co-existence of dugongs and seagrass beds. A habitat suitability model combines the point data set of dugong sightings within the continuous benthic habitat map and identifies the central western area as containing the most suitable habitat for dugong inside the Aldabra lagoon.