Reefs and islands of the Chagos Archipelago, Indian Ocean: why it is the world's largest no‐take marine protected area

Abstract

The Chagos Archipelago was designated a no-take marine protected area (MPA) in 2010; it covers 550 000 km2, with more than 60 000 km2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs.It contains 25–50% of the Indian Ocean reef area remaining in excellent condition, as well as the world’s largest contiguous undamaged reef area. It has suffered from warming episodes, but after the most severe mortality event of 1998, coral cover was restored after 10 years.Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless of whether the latter are fished or protected.Coral diseases are extremely low, and no invasive marine species are known.Genetically, Chagos marine species are part of the Western Indian Ocean, and Chagos serves as a ‘stepping-stone’ in the ocean.The no-take MPA extends to the 200 nm boundary, and. includes 86 unfished seamounts and 243 deep knolls as well as encompassing important pelagic species.On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in plantation times, but several smaller islands are in relatively undamaged state.There are now 10 ‘important bird areas’, coconut crab density is high and numbers of green and hawksbill turtles are recovering.Diego Garcia atoll contains a military facility; this atoll contains one Ramsar site and several ‘strict nature reserves’. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strict environmental regulations are enforced.Shoreline erosion is significant in many places. Its economic cost in the inhabited part of Diego Garcia is very high, but all islands are vulnerable.Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of the archipelago for this purpose.

A Geospatial Appraisal of Ecological and Geomorphic Change on Diego Garcia Atoll, Chagos Islands (British Indian OceanTerritory)

“…Observations of both erosion and inundation have been recorded elsewhere around Diego Garcia [1,12,16], which accord with evidence of retreat in the form of seaward and lagoonward erosion ramps and cliffing. The degree to which these represent a recent, climate change-driven departure from a longer-term accretion regime, is unclear.…”

“…They are supported by the submerged Chagos banks at the southern end of a linear array of islands that include the Maldives and Laccadives. The islands and their associated reefs are thought to be in pristine condition due to the absence of environmental pressures such as fishing, tourism, terrigenous sedimentation and pollution [1]. They support a wealth of marine biodiversity including live coral, reef fishes, coconut crab, turtle and bird colonies [1].…”

“…The islands and their associated reefs are thought to be in pristine condition due to the absence of environmental pressures such as fishing, tourism, terrigenous sedimentation and pollution [1]. They support a wealth of marine biodiversity including live coral, reef fishes, coconut crab, turtle and bird colonies [1]. The archipelago was designated the world's largest no-take marine protected area in 2010 (>550,000 km 2 ).…”

“…While the absence of a continuous monitoring program precludes a robust analysis at one particular site, islands within the wider Chagos region show variable change over the last 230 years. This includes the apparent submergence of three sandy islets previously observed at Blenheim atoll in the north [7] and island growth and fusion of six sandy islets at Egmont Atoll [1]. Regional sea surface temperature increases have reduced live coral cover through bleaching across several of the reef platforms, most notably the 1998 warming event associated with the El Nino Southern Oscillation [8].…”

Coral Bleaching and Mortality in the Chagos Archipelago

“…Importantly also, these reefs demonstrate that there is a distinction, usually overlooked, between the different sets of factors that might initially kill corals from those which might then inhibit recovery once warming has abated (Ateweberhan et al, 2011(Ateweberhan et al, , 2013. Many areas around the world including Chagos showed similarly severe coral bleaching and mortality after the severe warming event of 1998, but many of those which had ongoing, direct and local impacts recovered only slowly or not at all, while the reefs of Chagos, and others that had minimal local impacts, recovered their primary reef builders after about seven years and had regained a full canopy of large framework Acropora after 7-10 years (Ateweberhan et al, 2013;Sheppard et al, 2012). The reefs therefore provide information not only on effects of ocean warming on coral reefs in the absence of any confounding local factors such as pollution and over-extraction of resources, but also of what factors are important to subsequent recovery.…”