Environment of Chagos

Flora and Fauna of Chagos Archipelago

Photograph: Anne and Charles Sheppard/Chagos Conservation Trust

It is believed that the Chagos contains the world’s largest coral atoll and the greatest marine biodiversity which has one of the healthiest reef systems in the cleanest waters in the world, supporting half the total area of good quality reefs in the Indian Ocean. As a result, the ecosystems of Chagos have so far proven resilient to climate change and environmental disruptions.

The Chagos Islands have been colonised by plants since there was sufficient soil to support them – probably less than 4,000 years. The islands and their associated reefs are believed to be in unspoiled condition due to the absence of environmental pressures such as fishing, tourism, terrigenous sedimentation and pollution. 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 varieties of ferns as well as a wide variety of mosses, liverworts, fungi and cyanobacteria. The lagoon reaches a depth of 31 m in the center and can be broadly divided into three basins running from north to south that get progressively shallower and host more intricate topography, including coral knolls and limestone ridges.

They support a wealth of marine biodiversity including live coral, reef fishes, coconut crab, turtle (Endangered green (Chelonia mydas) and hawksbill (Eretmochelys imbricata), and bird colonies (such as Red Footed Booby, Brown Noddy, Sooty Tern, and Lesser Noddy). Over 175,000 pairs of seventeen species of seabirds breed on the atolls, and ten of the islands have formal Birdlife International recognition as Important Bird Areas.

A masked booby colony, Photograph: Anne and Charles Sheppard/Chagos Conservation Trust

Today, the status of the Chagos Islands’ native flora depends very much on past exploitation of particular islands. The existence of environmental gradients, especially from seaward to lagoonward shores, and the scale of human interference have combined to form patterns in the vegetation, including zonations and mosaics. Coconut plantations dominated the island vegetation community while the atoll was under English and French colonial control between 1876 and 1971. These were extensively cleared along the western atoll rim and several invasive species were added during construction of the airbase, beginning in 1971, but native vegetation remains in other parts of the island with some places transitioned through several successional stages including coastal grasses and sedges, littoral scrubs and hedges, a mixture of shrubs and juvenile trees, termed locally as “Cocos Bon-Dieu”, broadleaf woodland and planted coconut trees. 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. Some of these non-native species have become invasive and pose a threat to the native ecosystems, thus 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).

According to (Bourne (1886a, and 1886b) there are no native mammals in the Chagos Archipelago apart from the introduced mammals and other domestic animals found following 1885, such as donkeys, cats, dogs, hogs, fowls, rats, cattle and sheep; but later discovered that cattle did not thrive.

Marine Life

The Chagos anemone fish is found only in the Chagos Archipelago. Photograph: Alasdair Harris, Blue Ventures Conservation

Over 275,000 people and a number of NGO's called on the UK Government to establish the territorial waters of the Chagos Archipelago as a Marine Protected Area (MPA) in 2010. It is now the world's largest no-take Marine Reserve at 640,000 square kilometers, an area twice the size of the UK..

There are at least 310 species of coral on the reefs of the Chagos Archipelago, including the Chagos brain coral (Ctenella chagius), a species endemic to these waters. Corals not only created the tiny atoll islands of the Archipelago but thick strands of branching species continue to protect them from waves and storm damage. The total area of near-surface coral reefs is some 4,000 square kilometers, which is approximately 1.5% of the total global area of reefs, a very major proportion of an important and increasingly threatened global heritage.

The Chagos Archipelago supports a diverse array of sharks and rays from coastal reef sharks to pelagic species such as the Shortfin Mako, Blue and Oceanic Whitetip sharks which patrol the open-waters. Chagos is also home to majestic animals such as reef manta rays and whale sharks. The Chagos Marine Reserve also provides a temporary refuge for migratory species, such as tuna, from exploitation. 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 harbour many undiscovered and specially adapted species. (www.zsl.org)