With summer temperatures in the Arabian Gulf generally beyond the tolerance threshold of many coral species, forecasts of unusually warm seas this year are being met with trepidation by marine scientists.
Climate experts have predicted a high likelihood of extreme warming of the water this year because of the El Nino Southern Oscillation, a cyclical periodic shift in the Pacific Ocean that affects weather around the world. In 1997-1998, the phenomenon caused elevated water temperatures in many parts of the world, resulting in large-scale coral die-offs, known as coral bleaching.
In the Arabian Gulf, the highest magnitude of coral bleaching ever was observed, said Dr John Burt, an associate professor of biology at New York University Abu Dhabi (NYUAD). “We lost 90 per cent of the live coral in many of the reefs,” said the school’s head of the marine biology laboratory. “That had a devastating impact on reefs here and in the wider region. The reefs are still recovering.”
Warnings of a significant increase in water temperature this year have raised the concerns.
“Virtually all of the models were predicting a 90 per cent chance of an extreme El Nino event this year,” said Dr Burt.
During routine monitoring of local coral sites earlier this summer, Dr Burt recorded a higher than usual maximum sea temperatures of 32°C in the Gulf of Oman and 34°C in shallower waters near Abu Dhabi. Such temperatures were not unusual for the region at this time of year.
“It has not gone the way they thought it would,” he said, adding that experts were predicting a 60 to 70 per cent chance of moderate to strong warming.
Dr Burt and his associate, Dr Emily Howells, have also been monitoring reefs in Kuwait and Qatar. Their observations showed slightly higher water temperatures in Fujairah where some bleaching of corals was found and reefs were at risk.
Overall, however, a warming event capable of causing mass coral damage and die-off was unlikely.
“We are keeping an eye on things in case they change,” said Dr Burt, noting that August and early September were the highest-risk months for coral reefs.
Coral lives in a symbiotic relationship with marine algae, known as zooxanthellae. Algae lives in the coral tissue, which otherwise would be mostly transparent. Like plants, algae uses sunlight to photosynthesise, producing sugars the coral needs for sustenance.
Heat stress disturbs this symbiotic relationship. Around the world reefs thrive at temperatures of about 28°C. If the temperature is higher this can disturb the algal photosynthesis inside the coral tissue, resulting in the production of damaging oxygen radicals.
When the temperature rises above a certain threshold, coral starts expelling the algae from its tissue. Coral bleaching, as the phenomenon is commonly referred to, occurs when the white coral skeletons shine through the coral tissue, deprived of algal pigments. Bleached coral can sometimes recover but in many cases it dies.
In Australia, coral starts to bleach if the water reaches 31°C. In the Arabian Gulf, it starts at 35°C to 36°C.
While it is impossible to control natural fluctuations in water temperatures, governments can help to protect coral by ensuring additional stress factors are kept at a minimum, Dr Burt said.
“It is important to reduce any man-made stressors resulting from coastal development, nutrient input and intensive [scuba] diving.”