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.
Coral reefs are the most biologically diverse habitats of the oceans and provide essential ecosystem goods and services to hundreds of millions of people. 19% of the world’s reefs have been lost already and a further 35% may be lost by 2050. Remaining reefs are under pressure from pollution, over-fishing and climate change pressures such as rising sea temperatures. Reefs are facing a spiral of decline, as warming temperatures continue to drive mass coral bleaching while future acidification threatens recovery and future growth.
“From the perspective of these magnificent ecosystems, climate change has already gone too far” said Dr Charlie Veron, the world’s foremost authority on corals. “We believe that atmospheric CO2 concentrations of 350ppm represented a threshold for the world’s reefs”. Atmospheric CO2 is currently at 387ppm.
Coral bleaching is an increasing threat to coral reefs with a single event in 1997/1998 devastating an estimated 16% of the world’s coral reefs in one go. These early events were followed by re-growth of new corals, but heat-induced coral bleaching is now happening sufficiently frequently that few reefs can fully recover before they are hit again.
“It’s not just that the reefs are beginning to die” said Dr Mark Spalding, Senior Marine Scientist at The Nature Conservancy, “it’s what they take with them. These are the rainforests of the sea, but they are also critical to people. They may be the first and most sensitive ecosystems to succumb to climate change, but they will not be alone.”
“Reefs are highly sensitive ecosystems. For years, many have been weakened by human activities and this has left them highly vulnerable”, said Alex Rogers from the Zoological Society of London and the International Programme on the State of the Ocean. “Now we are also faced with the threat of acidification caused by the oceans absorbing CO2, with evidence indicating that the growth of reefs is already slowing down because of changes in ocean chemistry.”
Coral reefs in the Indian Ocean are under particular pressure from human activities, but the Chagos archipelago is the big exception. Almost 50% of the remaining reefs in good condition in this region can be found in Chagos. The Chagos is a vital stepping stone linking east and west Indian Ocean reefs and replenishing over-exploited habitats ‘down-stream’ in places like East Africa, where millions of people depend on reefs for food security.
Strictly protected from direct human pressures, Chagos forms a precious reference site against which to compare other reefs’ recovery. The Chagos Marine Reserve is a natural laboratory for scientists to study how a truly healthy reef lives and thrives in a changing world. As the challenges of climate change face all reefs around the world it is important for us to have a few good sites that can remain resilient to these pressures.