UAE's corals suffer 'catastrophic' damage in record summer heat

The future of eight reefs in the Arabian Gulf is in doubt after high temperatures and low winds leave corals dying
Daniel Bardsley The National 2 Feb 19;

Scientists fear the future of the UAE’s reefs is in doubt after research found rising temperatures killed almost three quarters of Abu Dhabi’s coral.

Record temperatures in the summer of 2017 left more than 90 per cent of Abu Dhabi’s coral cover bleached and struggling to survive, New York University Abu Dhabi found.

Dr John Burt, associate professor of biology, said there was a remarkable amount of damage.

“The results were catastrophic,” Dr Burt told The National. “I had never seen anything like it in my career.”

Coral in Saudi Arabian and Qatari waters have also been destroyed.

Damage to the reefs off Abu Dhabi reflects a global trend, driven by high emissions and rising temperature.

But local factors such as sewage discharge, dredging and land reclamation also stress coral, Dr Burt said.

Temperatures in the Arabian Gulf are rising faster than expected, harming the ecosystem, making the water saltier and compounding the problem of “hypoxia”, or low oxygen levels.

The destruction witnessed in the summer of 2017 was caused by winds being weaker than normal, reducing evaporation from the sea, which usually cools water down.

Over August and September that year, the maximum daily temperature at the reefs averaged close to 36°C, and coral endured nearly two months above bleaching temperatures and almost two weeks above lethal temperatures.

Within a month, 94.3 per cent of Abu Dhabi’s 120 square kilometres of coral cover became bleached, and almost two thirds died, a figure that rose to nearly three quarters by April last year.

Because average temperatures continue to rise, bleaching is becoming more and more common. There was more of it last summer, and this year researchers will analyse its effects.

Reef-building coral usually contains algae in a relationship that benefits both organisms.

The algae photosynthesise, producing oxygen, glucose and other food for the coral, while the coral provide the algae with a safe habitat and nutrients.

When temperatures rise, the algae photosynthesise more, leading to high oxygen levels that harm the coral, which then respond by ejecting the algae.

“This is coral in dire straits. It can live for a period of time living off its own fat reserves,” Dr Burt said.

“If the stress persists, it won’t take the algae back in. After two weeks or so you will start seeing coral dying.”

Dr Burt said the coral framework remained but much less of it was alive. In future, he said there would be more large algae and sponges living among the mostly dead coral framework in what will be a less-diverse habitat.

Bleached coral in the Arabian Gulf. Photo credit: Noura Al Mansoori. For a story by Daniel Bardsley
Bleached coral in the Arabian Gulf. Courtesy: Noura Al Mansoori
“My opinion, and the data backs this up, is that the prognosis for the future of the Gulf reefs is relatively grim,” he said.

“The water here is warming up three times faster than the global average because it’s a shallow basin.”

The coral can regrow but it needs more than a decade of uninterrupted growth, which is unlikely given the high frequency of warming events.

Coral also regenerates by producing larvae and Dr Burt said larvae produced by reefs off Iran and Bahrain may drift into the southern Gulf, producing coral to partly replace what has been lost.

He said there were efforts under way in Abu Dhabi to grow coral but these were “relatively small scale”.

“Reef scientists are working with policymakers to try to enact change but none of the international agreements have seemed to put a dent in the carbon dioxide emissions we’re putting in the atmosphere,” Dr Burt said.

His research group is developing a model that uses meteorological data to identify, two to three weeks in advance, when coral is likely to be most vulnerable to damage caused by high water temperatures.

This would alert government agencies, which could suspend activities that stress coral.

“You would be putting some of these projects on hold, not necessarily cancelling them. There would be negligible economic impact,” Dr Burt said.

Globally, there is no sign that the temperature increases of recent decades are slowing down.

“Unless there’s some serious mitigation, which there’s not much sign of, the oceans will carry on warming for the foreseeable future,” said Edward Hanna, a professor of climate science and meteorology at the UK’s University of Lincoln.