ABU DHABI // They have clung to survival in the Gulf's inhospitable waters for millennia, but key coral species could be wiped out altogether by rising sea temperatures.
Scientists are conducting a two-year study off the coast of Abu Dhabi to assess what coral species remain following an environmental disaster more than a decade ago, and how to repopulate them.
Ten reefs on the emirate's coastline are being examined in the collaborative study by New York University and the Environment Agency - Abu Dhabi (EAD).
A year into the research, it is clear that very little of a branching coral called acropora, which was once dominant across the coastal areas of the emirate, is still alive.
The species are crucial to reef-building - but in 1996 and 1998 the ripple effects of the El Nino weather event caused the temperature in the Gulf to rise, killing 98 per cent of them.
In their place, the more resilient Favidae family - "brain corals" - now dominates the reefs. But the rises in temperature put tremendous stress on them, too.
John Burt, a marine biologist and assistant professor at New York University Abu Dhabi, is one of the scientists conducting the new study. "We had already lost the most sensitive species in 1996, but the 1998 event affected the most tolerant species," he says. "It caused declines of 40 to 60 per cent of the remaining coral."
Charles Sheppard, professor of life sciences at Warwick University in England, has studied the effect of temperature increases in the Indian Ocean and the Gulf following the El Nino event in 1998.
He found that corals die during peak temperature periods known as degree weeks. If the temperature is just a degree above the norm for a period of 10 weeks, or by two degrees for five weeks, corals can be killed.
At one stage, temperatures off the coast of Abu Dhabi reached 37.7°C. "That's the hottest I've ever heard of in my life for a temperature on a reef, anywhere on earth," says Dr Burt.
Extreme temperatures can cause corals to bleach, as the single-celled algae that exist in symbiosis with the coral polyps - the thousands of genetically identical, jellyfish-like organisms that make up a coral colony - are expelled.
"The project we're involved in now is to look at what recovery has there been from these massive bleaching events, in 1996 and 1998," said Dr Burt. "But so far it has been limited.
"We've had population declines which are so significant that the natural recovery of these reefs, through the supply of larvae and the water column, is not sufficient to induce recovery."
But tourists want pristine, living reefs - and to that end plans are afoot for areas off the coast of Saadiyat island to be transformed into a carefully maintained marine park. Nothing has been fully approved yet, though, according to Ashraf al Cibahy, the manager for marine protected areas at EAD.
The natural reef off the island is one of three in the emirate that still has branching corals, although only barely. The other areas are the al Dhabeiyah reef and Ras Ghanada, a large reef near the Dubai border.
EAD has already begun to look at ways to repopulate the coral community. In a joint project between EAD and the Tokyo University for Marine Science and Technology, six "coral settlement devices" were dropped off the coast of Saadiyat and al Dhabeiyah in May of last year.
The doughnut-shaped calcium carbonate structures were meant to act as a substrate material for coral larvae (that is, the larvae could live on them). So far, though, there has been little sign of that happening.
"These discs are currently under evaluation to see if they are feasible," said Mr al Cibahy. "So far we have seen very little coral juveniles. However, it is still less than one year after being introduced."
Most of the species in the UAE reproduce sexually, ejecting an orange slick of eggs and sperm that fertilises and settles on a suitable substrate.
Spawning occurs simultaneously across the entire reef, with all organisms suddenly ejecting their genetic material at once, often at full moon.
The precise date of spawning of corals in the Emirates is not known. Some scientists believe it is in March or April, while others say there are signs it could be in July or August.
The date is crucial. If the settlement devices were dropped after last year's spawning, it is still possible that the project could be far more successful this time round.
Even if coral does begin to grow, it will eventually need to be transplanted on to the reef - a process that has only a 60 per cent chance of success, according to Mr al Cibahy.
Most larvae die before they settle, with fish or other marine species consuming all but one per cent of them.
There is, says Dr Burt, a study in the region - not yet formally announced - that involves collecting the larvae and propagating them in an aquaculture facility, before transplanting them back to the reef.
Nothing similar is being done in the UAE yet, although Dr Burt is looking into the possibility. "If we wait for natural processes it's going to take decades before these reefs get to where they were before 1996," he says.
Providing artificial substrate in the seawater or propagating organisms in coral farms are the two main methods for encouraging coral growth, he said. "However, most of them are not well studied and certainly not within the context of the harsh environment that we have here. This is an area which is open for research.
"We do need to understand what techniques work best in this environment, which species are most appropriate for selection for propagation in this area, where we should be propagating them. There's discussion in this area but it's not developed at this point."
Even if the coral communities are entirely repopulated, there is still the possibility of a recurrence of the kind of temperature increases seen a decade ago.
"The underlying trend is that sea temperatures are rising," says Dr Sheppard. "But it's not the average temperature which does the killing, it's the peaks. They are irregular and nobody can predict them.
"The best hope is that the corals can acclimate genetically to cope with the higher temperatures but they haven't done so far.
"The prognosis is not good at all," he says. "It's difficult to be optimistic."