The British Indian Ocean Territory (Chagos Archipelago) – An Environmental Evaluation

Sheppard, C.R.C, Sheppard, A.L.S. (2018). British Indian Ocean Territory (Chagos Archipelago). In: Volume 2 Chapter 11, World Seas. An Environmental Evaluation. pp 237-252. Academic Press, London, San Diego.


The atolls and reefs of the British Indian Ocean Territory cover approximately 60,000 km2 in the centre of the Indian Ocean. The atolls have not been inhabited for about 50 years apart from a military facility located in the southernmost atoll of Diego Garcia. All 640,000 km2 of territorial waters except those immediately around Diego Garcia were declared a no-take MPA in 2010. Shallow substrate consists mainly of coral reefs, though there are also some large patches of seagrass, but most of the area has not been explored scientifically. Until recently, the archipelago probably contained half of all reefs in the Indian Ocean that remained in good condition, supporting a reef fish biomass 6–20 times greater than anywhere else in that ocean. Between the atolls and banks, and further offshore, water is a few km deep. Changes to the reefs in the past few years have been drastic, with near-complete mortality of corals and soft corals in water to at least 15 m depth on all atolls that have been examined to date. Mortality was caused by warming water; measurements show that the average water temperature at several depths has risen from between 0.3°C and 0.5°C over the past decade. Levels of marine pollution are extremely low for all analyzed substances except for marine-borne litter and microplastics. The area is an important reference site because here ecological changes are caused entirely by ocean warming, without confounding effects from human use and pollution.

On islands, the ecology was badly damaged during the 200 years of coconut plantation, but some recovery in the past few decades is noted. Management is minimal and needs to be strengthened to ensure that poaching is reduced, and to help return some islands to a pre-man condition to allow the bird life to increase.

DOI: 10.1016/B978-0-08-100853-9.00015-4