A diver surprised by a school of fish in the reefs surrounding Chagos
Deep ocean
The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features (such as 6000m deep trenches, oceanic ridges, and sea mounts). These areas almost certainly harbour many undiscovered and specially adapted species. Although the deep-water habitats surrounding the islands have not been explored or mapped in any detail, work elsewhere in the world has shown that high physical diversity of the sea floor is closely linked to a high diversity of species.
The animals of the Chagos are truly unique in the region in terms of both their diversity and the healthy numbers in almost all populations. Keeping them that way will be the foremost priority of the Chagos Protected Area.
Coconut Crab (Birgus latro)
Coconut Crab (Birgus latro)
The coconut crab is the world’s largest terrestrial arthropod, reaching over one metre in leg span and 3.5-4 kilos in weight. As a juvenile it behaves like a hermit crab and uses empty coconut shells as protection but as an adult this giant crab climbs trees and can crack through a coconut with its 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, but also as ornaments for sale to tourists and as bait for fish traps. Demand for coconut crabs as souvenirs is strong, and other threats include habitat destruction and predation from introduced species such as rats.
The coconut crabs on Chagos constitute one of the most undisturbed populations in the world. An important part of their biology is the long distances their young can travel as larvae. This means the Chagos coconut crabs are a vital source for replenishing other over-exploited populations in the Indian Ocean region.
The Fish Tree Poison Flower
(Barringtonia asiatica). Photo (c) John Topp/Chagos Conservation Trust.
Plants
The Chagos Islands have been colonised by plants since there was sufficient soil to support them – probably less than 4,000 years. Seeds and spores arrived on the emerging islands by wind and sea, or from passing sea birds. The native flora of the Chagos Islands is thought to comprise 41 species of flowering plants and 4 ferns as well as a wide variety of mosses, liverworts, fungi and cyanobacteria.
Today, the status of the Chagos Islands’ native flora depends very much on past exploitation of particular islands. About 280 species of flowering plants and ferns have now been recorded on the islands, but this increase reflects the introduction of non-native plants by humans, either accidentally or deliberately. Because some of these non-native species have become invasive and pose a threat to the native ecosystems, plans are being developed to control them. On some islands, native forests were felled to plant coconut palms for the production of copra oil. Other islands remain unspoiled and support a wide range of habitats, including unique Pisonia forests and large clumps of the gigantic fish poison tree (Barringtonia asiatica). Unspoiled islands provide us with the biological information that we need in order to re-establish the native plant communities on heavily altered islands.
