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Back-to-Back Bleaching Events in Chagos Show Global Impact to Coral Reefs

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Bleached Corals in Chagos (Picture Anne Shephard)

Following reports of the back-to-back bleaching events that hit the Great Barrier Reef in the last few years, evidence has emerged of a mass bleaching following the same pattern in the Chagos archipelago in the Indian Ocean.

Chagos, a British Indian Ocean Territory 300 miles south of the Maldives and probably better known as the location of a US Military base on Diego Garcia, the largest of the islands, is home to one of the largest marine protected areas in the world, stretching across 250,000 square miles of ocean.

As Diego Garcia is the only populated island of the 60 or so that make up the Chagos Archipelago, the damage to the otherwise pristine coral appears to provide confirmation that abnormally elevated sea temperatures are solely responsible for the bleaching events.

Reports from 2016 estimate up to 85 per cent of the coral reefs in the marine park were damaged or had died during the year, brought on by what is known to be a much larger El Nino event than has occurred in previous years.

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Pictures of the reef taken before and after the mass bleaching event (Pictures: John Turner, University of Bangor)

A similar event in 1998 caused damage to the reef that took until 2012 to recover, but the measured water temperatures in 2016 appear to be 1℃ higher than in 1998.

Professor John Turner, of the University of Bangor in Wales, who led the most recent expedition to the archipelago said in an interview that, ‘in shallow water, above 15 metres and in places down to 20 metres, we've seen a lot of coral mortality - probably somewhere in the region of 90 per cent’

A short report on the Chagos Conservation Trust website by Jon Slayer, indicates that a dive in December 2016 at a previously vibrant reef indicated ‘almost 100 per cent mortality,’ along parts of the reef.

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Bleached Corals in Chagos (Picture Anne Shephard)

Coral bleaching – a phenomenon created by elevated water temperatures which lead to individual coral polyps ejecting the symbiotic algae (zooxanthellae) which live inside them – is a naturally occurring event, and most reefs will recover over time as the water temperature returns to normal.

The sustained rise in temperatures over the last two years, however, has meant that the coral has had no time to recover, and the prolonged absence of the algae causes the coral to die.

With two of the world’s largest reef systems clearly indicating that the mass bleaching events are a global problem – and especially in Chagos, which has otherwise been relatively unscathed by human activity – only time will tell if continued warming events will allow the coral to recover.

More information can be found on the Chagos Conservation Trust's blog


Before and After video from Jon Slayer at the Chagos Conservation Trust

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