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.
A Chagos clownfish (Amphiprion chagosensis). Photo (c) Chas Anderson
Fish – General
Chagos is home to at least 784 species of fish that stay near to the shores of the islands including the endemic Chagos clownfish (Amphiprion chagosensis) and many of the larger wrasse and grouper that have already been lost from over-fishing in other reefs in the region.
As well as the healthy communities of reef fish there are significant populations of pelagic (open ocean) fish such as manta rays (Manta birostris), sharks and tuna. Sadly, shark numbers have dramatically declined as a result of illegal fishing boats that seek to remove their fins and also as accidental by-catch in the two tuna fisheries that operate seasonally in the Chagos. Skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) are caught for about two months of the year as their year-long migratory route takes them through Chagos waters. The international fleet that follows the schooling fish take 95,590 – 24,784 tonnes of target species (i.e., this figure does not include bycatch) per year while in Chagos waters. By declaring the Chagos a strict no-take marine reserve populations of all these species would be freed from fishing pressures as long as they were within the reserves protective boundaries.
Ctenella chagius, the endemic brain coral of the Chagos
Corals
The reefs of the Chagos are home to at least 220 species of coral including the endemic brain coral (Ctenella chagius). The coral cover is dense and healthy even in deep water on the steep outer reef slopes. Thick stands of branching Staghorn coral (Acropora sp) protect the low lying islands from wave erosion. Despite the loss of much of the coral in a bleaching event in 1998 the recovery in the Chagos has been remarkable and overall coral cover increases year on year.
For more information about the threats faced by coral reefs worldwide, and why the Chagos reefs are special, please see our Reefs in Crisis page.
