Coral Reefs of the Chagos Archipelago, Indian Ocean

Coralcover throughout the Chagos archipelago is high. Coraland soft coralmortality was very severe in 1998, along with most of the ocean, but there are no direct human impacts so that soft coraland coralcover is as high as it was before the massive mortality episode. There is a very low incidence of coraldisease, and there are no recorded marine invasive species, a condition which is unprecedented in coralseas. The area contains between 25 and 50 % of the reefsin the Indian Ocean in very good condition, and the area has the largest contiguous area in the world of reefsin such a state. Reasons for the good condition of Chagos reefsare likely to include remoteness from compounding human activities, but also strongly light adapted‘Clade A’ zooxanthellaemay contribute: these occur in approximately half of the shallow water Acroporacolonies which are now recovering strongly. Another contributing factor may be the regular incursions of deep, cool water that rise to cover reefs, including during annual periods of greatest warming. These reefsare viewed as a ‘baseline’ or reference point for many other coralrees in the Indian Ocean.