Threats to the Chagos Archipelago

While the archipelago has not been as devastated as other ecosystems around the world, it still needs protection from several threats.

Invasive species

When humans first discovered the archipelago in the 1700s they introduced several invasive species including rats, and cleared native forest and vegetation for habitation and the creation of coconut plantations. Coconut farming ceased in the 1970s but as a legacy of the plantation era, every island farmed for coconuts has rats. 

Rats decimate the native plants and important seabird populations by eating eggs and chicks. Today, the 30 rat infested islands have significantly fewer, to no, seabirds, particularly ground nesting species. 

The Chagos Conservation Trust’s Healthy Islands, Healthy Reefs programme is an ambitious and exciting large-scale rewilding project that will reduce the damage caused by rats and loss of habitat.

Creating a rat free archipelago will result in three and a half times more habitat available for seabirds.

Invasive species - including black rats - have affected the native species and habitats of over half the islands

Climate change

Rising global temperatures have had a dramatic effect on coral reefs. Warming seawaters have caused coral colonies to "bleach", by affecting the symbiotic algae which are sensitive to light exposure, temperature and acidity. The depletion of algae and coral leads to the loss of vital habitats for a variety of species.

The archipelago saw a coral bleaching event in 1998 with rapid recovery seen in some parts of the archipelago.

Over the last decade, it has seen two more significant episodes of coral bleaching due to extreme sea temperatures, resulting in high levels of coral death, and a reduction in how well the reefs function. 

The 2015 ocean heatwave killed 60% of the hard corals at depths of up to 10 meters across the archipelago, with some species more affected than others. For example, 86% of Acropora corals, previously the most abundant, perished.

Before corals were given a chance to recover another heatwave struck just one year later and data collected from the Peros Banhos Atoll showed that 68% of the remaining hard corals were bleached and 29% died, suggesting that approximately 70% of hard corals were lost between 2015 and 2017 overall.

Illegal fishing

Before the designation of the marine protected area, an estimated 10,000 sharks and 10,000 rays were killed annually by the licensed fishing industry. While protection has ended legal fishing within its waters, illegal fishing continues to affect sharks and other valuable species such as tuna and grouper.

It is often hard to detect the small illegal boats, which hail from Sri Lanka and more recently India. Patrol vessels are tasked with policing more than half a million kilometres of ocean. But modern technology is being employed to address the problem, and a £100,000 fine can be imposed on those who are apprehended.

However, the very richness of these waters, compared with the increasingly over-fished and impoverished waters elsewhere in the Indian Ocean, means that the marine protected area is likely forever to be attractive to poachers.

Indian Ocean shark numbers have decreased by 90% over the last three decades