Chagos coral hard-hit – and first thresher spotted

archive – Diving News

Chagos coral hard-hit – and first thresher spotted

Chagos Archipelago, the remote chain of seven atolls in the Indian Ocean long held up as one of the world's most pristine coral reefs, has been hit by severe bleaching and die-off of its shallower corals.

A team of 14 scientists led by Prof John Turner from Bangor University’s School of Ocean Sciences recently completed an expedition to the archipelago, which lies in one of the world’s largest marine protected areas, the British Indian Ocean Territory.

The territory covers an area the size of France and has been largely uninhabited since 1971, when the UK evicted the inhabitants to allow the USA to develop the Diego Garcia naval base. Apart from its coral, Chagos Marine Reserve contains significant populations of endangered species including sharks and turtles and, says the university, has provided a benchmark for reversing damaged eco-systems elsewhere.

The scientists spent three weeks aboard the reserve patrol vessel Grampian Frontier to assess how coral reefs in three of the atolls had been affected by the warming events of the past two years.

Diving exposed seaward reefs, leeward lagoon reefs and patch reefs to a depth of 25m, they reported that, although corals below 15m were generally in good health, most of those above that depth – apart from the often very large porites – had died. Many large table corals had collapsed, and at exposed sites had been swept off the reef, taking young corals with them.

On exposed seaward reefs, coldwater upsurges appeared to be helping to protect deeper-lying corals.

“We are obviously saddened to see the coral reefs of Chagos in this state, which is no different to that of other climate-affected locations such as the Great Barrier Reef,” said Professor Turner.

However, he added that he “remained optimistic that these reefs, protected and remote from human impacts, can still bounce back as they did after the 1997/98 warming event.”

He added that a highlight of the expedition was an encounter with a thresher shark, the threatened pelagic that visits reefs for cleaning but had not been sighted in Chagos before.

“The shark was as surprised as I was, and used a flick of its immense tail to speed away into the blue.”

The expedition was funded by the Bertarelli Foundation through the Zoological Society of London.

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