Chagos Biodiversity and Threats
Located 500km south of the Maldives, the tropical reefs and islands of the Chagos archipelago cover an area of approx. 19,000km2 in the British Indian Ocean Territory. It has a huge diversity of marine and terrestrial species, with soem of the most undisturbed coral reefs in the world in. This incredible diversity is under threat — at least 76 of Chagos' species are already on the IUCN Red List.
Vibrant Reefs
The largest and most southerly island, Diego Garcia, contains a joint UK-US naval support facility, whilst most of the other islands are uninhabited. Due to this islands' remote location, relatively low human population, and unpolluted waters, there are over 220 coral species in Chagos.These include shallow water species like brain coral to those living on the deep-water shelves such as staghorn corals. See our coral collection gallery
The worsening state of reefs worldwide and increasing frequency of large-scale coral bleaching is due to ocean acidification , changing sea levels and other threats. Chagos lost about 90% of its reefs in a mass-bleaching even in 1997-8, but has had a good recovery with almost 50% of the remaining reefs in good condition. Chagos provides an important benchmark for coral conservation, and is a 'natural laboratory' in which we can study the functioning of these wonderfully complex ecosystems. Read about climate change threats.
Flourishing Marine Species
Chagos is home to at least 784 species of fish, including the endemic Chagos clownfish (Amphiprion chagosensis) and many species already lost from over-fishing in other reefs in the region. There are also significant populations of open ocean fish such as manta rays (Manta birostris), sharks and tuna.
Sadly, shark numbers have been decimated by illegal fishing for fins and the accidental by-catch of the two tuna fisheries that used to operate in Chagos. The strictly no-take Chagos Marine Reserve has freed Chagos' fish populations from fishing pressure within the reserve’s boundaries. This is of particular importance for globally threatened species, such as the silky shark.
Chagos' remote islands are nursery sites for green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles. These species are both classed as Critically Endangered in the IUCN red List, so these breeding sites are invaluable, and the reserve is vital to protect them from human exploitation.
The reefs are not the only sites of high diversity. From what we have found so far, the deep water habitats surrounding the archipelago are highly varied habitats, with 6000m deep trenches, oceanic ridges, and sea mounts, and are likely to contain a high diveristy of deep-sea species to match.
Diversity on Land
Many islands in the Chagos Archipelago are home to vast breeding colonies of 17 different species of seabirds. These species include sooty terns and red footed boobies, fairy terns and wedge-tailed shearwaters. Because of this huge avian diversity, Birdlife international designated ten of these islands as Important Bird Areas. These colonies are, however, threatened by the damage from invasive rats, overfishingm of their prey, and habitat loss.
One of the most spectacular inhabitants of Chagos shores is the coconut crab (Birgus latro), the world’s largest terrestrial arthropod at over a metre wide and 3.5-4 kilos in weight. As a juvenile it behaves like a hermit crab, living in empty coconut shells, while adults can crack through coconut shells with their massive claws. Despite its wide global distribution, it is rare in most of the areas it is found. It is primarily threatened by over-collection for food and souvenirs. The coconut crabs on Chagos form one of the most undisturbed populations in the world.
