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.
Bigeye tuna (Thunnus obesus) caught on a longline. (c) Sutton-Hibbert/Greenpeace
Bigeye tuna (Thunnus obesus)
Bigeye tuna (Thunnus obesus) are deep water fish, occupying almost all the world’s oceans within about 45º of the equator. With a diet of fish, cephalopods and crustaceans, and a migratory nature, the adults roam deeper waters whilst juveniles often associate with floating objects acting as fish aggregation devices.
As one of the larger tuna-fishes they can reach 2.5m in length with up to 200kg of high performance muscle. Tunas have an unusual amount of red, blood-rich sprinting muscle (hence the colour of sashimi) which makes them some of the fastest fish in the oceans.
Bigeye tuna are one of the most sought after and commercially important species of tuna, and as such, the IUCN lists them as Vulnerable and many stocks globally show signs of depletion.
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 Marine Reserve.
