Chagos Archipelago: A Case Study in Rapid Reef Recovery

Provided by Dr. Charles Sheppard, University of Warwick

Photo credit: Charles Sheppard

The Chagos Archipelago in the central Indian Ocean is a group of atolls, submerged atolls, and reefs scattered throughout an area of 60,000 sq km. The archipelago is home to the most geographically isolated reef system in the Indian Ocean, in terms of both distance and ocean current patterns. Local human influence is low, as most of the archipelago is uninhabited; only the military base on the atoll Diego Garcia is populated. In April 2010, the British government designated the entire Chagos Archipelago as a marine protected area. Prior to this designation, most islands and surrounding reefs were nature reserves with restricted access.

The reef system of Chagos lost more than 80 percent of its shallow corals and almost all its soft corals during the 1998 mass bleaching event.¹ The reefs also suffered extensive bleaching in 2003 and 2005, but in neither of these more recent cases was there subsequent mass mortality such as in 1998.

Recovery from the bleaching event of 1998, including recruitment of juvenile corals and recolonization, has been rapid, more so than many other locations equally affected by the 1998 event, and this has been attributed to the lack of direct or local human impacts in Chagos. Regeneration of coral cover has been greatest in shallow waters (especially among Acropora palifera), and in deeper waters, three-dimensional structures and complexity have shown rapid recovery (especially among the faster-growing, tabular Acropora cythera).²

Today, the number of reefs around the world without direct human impacts is extremely small, so Chagos represents the rare case where scientists can examine effects of global climate change in the absence of human influence. The recovery of corals in Chagos—in comparison to other sites in the region under greater human pressures—therefore highlights the importance of local management efforts to reduce these pressures.

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