The scientists cranked the heat above the lethal threshold, and waited for the corals to die.
“We were heating the water one degree above the summer maximum temperature,” says Anders Meibom, a researcher with the Institute of Earth Sciences at the University of Lausanne. “On the Great Barrier Reef, after a couple of weeks of that they’d start dying.”
But the corals taken from the Gulf of Aqaba, a trench of water that protrudes from the Red Sea, lapping Jordan, Israel, Saudi Arabia and Egypt, appeared untroubled by the temperature.
“So we increased to two degrees,” Meibom recalls. “Now, they’re supposed to die. Instead they looked happier.”
They raised the heat again. “Three degrees now, this is ridiculous,” Meibom says. “We were thinking, this is nonsense – they’re supposed to be dead. But they didn’t even look stressed. So, we went up to four degrees.”
Coral science in past years has become the study of an ecosystem in freefall. Coral reefs, some of the world’s richest environments, are regularly undergoing mass “bleaching” as a result of abnormally high ocean-surface temperatures and increased acidification, both consequences of global heating. The loss of colour – the result of an expulsion of the microscopic algae that sustains the creatures – is a vivid sign that corals have become severely vulnerable to further heat and disease.
Half the world’s coral reefs are thought to have died in the past three decades, and up to 90% of existing coral reefs may die by the middle of the century, according to research from February.
Yet the coral in the experiment at the University of Eilat survived, even as temperatures were raised to five, then six, then seven degrees. “They even showed improved physiological performance at higher temperatures,” says Maoz Fine, the professor of marine science who led the research. “At first we weren’t so sure we were doing everything right, experimentally.”
Their results confirmed years of reports from divers in the Gulf of Aqaba and northern Red Sea. Despite ocean-surface temperatures in the area warming at the same rate as elsewhere, coral species there have never suffered a documented bleaching event. A growing body of research from across the region is leading marine scientists to a compelling possibility: that a large range of corals along the 4,000km Red Sea reef are uniquely resistant to the climate crisis.
“We realised, holy shit, we have an unbelievable situation,” Meibom says. “This is the only coral reef ecosystem that has a chance to withstand the two-to-three degrees of extra heat that we’ll now unavoidably have by the end of the century.”
If it can survive the neighbourhood. Protecting the reef from other threats such as pollution and overpopulation will require one thing above all, the scientists say. Persuading at least four Middle Eastern governments – not all of whom recognise each other’s existence – to work together.
The Red Sea feeds into the Indian Ocean through a shallow strait between Djibouti and Yemen about 30km wide. More than 2.5m years ago, during the last ice age, the strait receded, cutting off the Red Sea and rendering it inhospitable. “It got super hot, super salty and just about everything died,” says Karine Kleinhaus, a professor of marine science at Stony Brook University in New York.
When the ice caps melted, the strait reappeared, and plant and animal life flooded back. The coral species that made the arduous journey north through the Red Sea underwent generations of evolutionary selection. “Only those who could withstand the very high salinity and temperatures could move north and colonise,” Kleinhaus says.
Many of the coral species that inhabit the Red Sea reef today were forged by that migration, scientists believe, and can survive, and even flourish, in ocean temperatures hotter than those forecast in the decades ahead.
The implications for coral reefs elsewhere in the world are still being studied. Transplanting hardy coral species to other reefs has not generally worked in the past, says Meibom. “The salinity of the water and the ecosystem of microbes is different,” he says. “A few species survive, but they’re not happy, and many of them die.”
Another possibility is figuring out exactly how Red Sea corals survive extreme conditions, and then steering the evolution of species elsewhere to select for those qualities.
The problem is that scientifically assisted evolution still takes time, and reefs are being pummelled by heat waves at an accelerating rate.
Research into the Red Sea corals is still in its early stages. “We don’t really know what is going on biologically that allows these corals to thrive with temperature disruptions that are killing coral in other places,” Kleinhaus says.
Progress is being slowed by lack of funds and shutdowns and travel restrictions as a result of the coronavirus, but also the region’s tense politics. Gathering scientists from across the region to mount a research expedition at different points in the reef, for example, has been hampered by Saudi Arabia’s reluctance to allow Israeli scientists in its territorial waters. “Everything is a challenge in this region,” Fine says.
Threats to the reef will accumulate in the decades ahead. Populations along the Red Sea in Israel, Egypt and Jordan are expected to surge. Saudi Arabia is planning to build a futuristic megacity on the edge of its waters. “Even though the reef is resistant to climate change, it’s not going to be immune to unsustainable development, pollution, sewage, or hyper-saline discharge from desalinisation plants,” Kleinhaus says.
No one country can protect it alone, says Olivier Kuttel, from the Swiss Federal Institute of Technology in Lausanne. “Egypt can do well, but if Saudi Arabia, Israel or Jordan do poorly, they can very rapidly destroy the whole ecosystem,” he says.
Jordan’s King Abdullah II is among those lobbying to have the reef recognised on Unesco’s Marine World Heritage List, which proponents hope will raise the status of the area, make it easier to attract funding for research and pressure governments to protect it.