Coral Reefs of the Chagos Archipelago, Indian Ocean

Coral cover throughout the Chagos archipelago is high. Coral and soft coral mortality was very severe in 1998, along with most of the ocean, but there are no direct human impacts so that soft coral and coral cover is as high as it was before the massive mortality episode. There is a very low incidence of coral disease, and there are no recorded marine invasive species, a condition which is unprecedented in coral seas. The area contains between 25 and 50 % of the reefs in the Indian Ocean in very good condition, and the area has the largest contiguous area in the world of reefs in such a state. Reasons for the good condition of Chagos reefs are likely to include remoteness from compounding human activities, but also strongly light adapted ‘Clade A’ zooxanthellae may contribute: these occur in approximately half of the shallow water Acropora colonies 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 reefs are viewed as a ‘baseline’ or reference point for many other coral rees in the Indian Ocean.