The super-corals of the Red Sea


Images of white, skeletal coral reefs are becoming an increasingly bleak, if familiar sight. Massive coral bleaching events are becoming more common around the world, as a result of the rapid pace of climate change. In the period from 2014 to 2017, about 75% of the planet’s tropical coral reefs suffered heat-induced bleaching during a global ocean heatwave.

A “bleached” coral is a stressed-out coral that, when triggered by environmental changes such as pollution and warming waters, has evicted its beneficial, energy-producing algae. Without these symbiotic algae, the coral loses its colour and appears white. Recovery from bleaching can be possible, but it’s not guaranteed. More frequent bleaching events mean less time for the corals to bounce back. Those that don’t recover, die – and their ecosystem can collapse with them.

“As we see the frequency and intensity of mass bleaching events increasing, the situation is becoming more dire,” says Andréa Grottoli, a professor in the School of Earth Sciences at Ohio State University. Grottoli’s research is focused primarily on the effects of climate change on coral reefs and what it is that makes some corals more resilient than others. “The models are projecting catastrophic losses in reefs by the end of this century.” Indeed, the majority of the world’s coral reefs are predicted to die by the end of this century, if not sooner.

Yet, at the northern end of the Red Sea in the Gulf of Aqaba there is a ray – or, rather, reef – of hope. Coral reefs in the Gulf of Aqaba appear to be “content” with the increasing temperatures, as Anders Meibom, a geochemist running the Laboratory for Biological Geochemistry at the Ecole Polytechnique Fédérale de Lausanne (EPFL) and Institute of Earth Sciences in Switzerland, puts it.

“Despite sea temperatures rising faster [in this region] than the global average rate, no mass bleaching events have occurred in the northern Red Sea,” says Jessica Bellworthy, a dive guide and tropical coral doctoral student at Bar-Ilan University, who works in the coral research lab at the Interuniversity Institute for Marine Sciences on the Gulf of Aqaba in Eilat, Israel.

Maoz Fine, a Bar-Ilan University professor who leads this lab, first noticed that there was something distinctly different about the Red Sea reefs when he returned home to Israel in 2005 after researching reefs in Australia. Fine expected to see more degrading reefs of the kind he was used to there. But what he found in the Gulf of Aqaba were corals apparently unaffected by ocean acidification and the steadily warming waters.

In 2010, Fine designed a prototype of what would become the Red Sea Simulator (RSS), a large-scale, multiple aquarium system with the ability to simulate future ocean conditions and run experiments that might shed light on what it is that makes the corals here so resilient.

With this system at the Gulf of Aqaba, the team is able to study corals and water from the Gulf, and adjust the acidity and temperature in the tanks according to their experiments. Multiple aquariums mean that more researchers can run experiments simultaneously, in the hope to better understand the physiology and genetics of the reef ecosystems.

“Coral reefs are biodiversity reservoirs and significant sources of food, income, and pharmaceuticals. We have a small window of opportunity remaining to apply science to rescue the world’s degrading reefs,” says Karine Kleinhaus, a professor in the School of Marine and Atmospheric Sciences at Stony Brook University. “But unless we uncover what exactly happens biologically in the corals of the Gulf of Aqaba that allows them to withstand warming temperatures, we don’t know how or if this knowledge can be applied elsewhere.”

Of particular interest, Kleinhaus says, are any important ecological factors in the reefs that “amplify any innate coral resilience or potential to recover from bleaching”. These could be particular phases of reduced pollution in the water, or periods of relief from overfishing.

Today, the RSS is 88 aquariums strong. All can be controlled remotely, allowing researchers to monitor them and make adjustments from wherever they are in the world – particularly important given that obtaining a visa to work in Israel is not always easy for some researchers. So far, the team has tested about 20 different species of Red Sea corals in the Gulf of Aqaba and found them much more tolerant of increased temperature.

Typically, a 1-2C increase beyond the summer maximum temperature would cause corals to dispel their algae and, often, die. Meibom and Fine’s unpublished research suggests that, while resilience varied between the corals they tested, overall, the corals easily withstood 4-5C above the current summer maximum. Some have even survived as much as 7C above the summer maximum. 

Not only are these corals proving resilient, but actually appear to do better in warmer waters. In some cases, their symbiotic algae doubled the amount of oxygen they produced and showed a 51% increase in primary productivity.

The secret to the Red Sea corals’ strength is thought to be a product of their past.

“This population of corals [in the northern part of the Gulf of Aqaba] migrated into the Red Sea system from the south where the temperature of the water is – and always was – high,” Meibom says. As you move north, the water temperature drops. Over thousands of years, some of these corals migrated north to where they now live at lower temperatures – today the Gulf of Aqaba is 27-28C.

But, it seems these corals retained their capacity to live at higher temperatures. “They still remember in their biology how to live at 33C,” says Meibom. “So if you increase the temperature to 31C, for example, they’re still happy.”

Other corals around the world don’t typically possess the same biological ability to persist. Given the global climate warming trajectory we are on – headed for a 2-3C increase or more by the end of the century, only corals that are now living well below their maximum temperature will be able to tolerate that change.

At this rate, the Red Sea reefs could be one of the last standing by the year 2100. “We know of corals in other regions that live in very hot water and survive,” Fine says, “but none that have such a large gap between the summer maxima and their bleaching threshold.”

And as one of the last coral reefs to survive, the Red Sea reefs could potentially “form a refuge where it becomes one of the few remaining reefs with full ecosystem function”, says Grottoli. “It could serve as a model for restoration once climate change stress is mitigated and we start being able to actually reintroduce coral… it could serve as a model for what a normal reef might look like.”

But in order for it to serve as a refuge and possible model in the future, it will need to survive more than the rising temperatures; nutrients and heavy metals from human activity such as unchecked coastal development, agricultural and wastewater runoffs, boats and fish farming could be the super-corals’ kryptonite. When Fine and the team introduce nutrients such as nitrate, ammonium and phosphate into the experiments, the corals’ physiology is compromised and they’re no longer as resilient. “It’s not enough to be resilient to temperature,” Fine says. “If we are to secure the Gulf of Aqaba and the northern Red Sea as a coral reef refuge, we have to remove the local stress.”

Along with Fine, Meibom, and several other scientists and diplomats, Kleinhaus is calling on Unesco to declare the Red Sea reef as a Marine World Heritage Site, to help ensure that the reef persists and will be protected from local threats that could otherwise compromise the coral’s resilience. 

The Red Sea project faces challenges that stretch beyond the borders of science and into diplomacy. Fine, Meibom and their team are planning an ambitious expedition to sail on a research boat called Fleur de Passion from the north to the south of the Red Sea. The expedition may inevitably be delayed by the coronavirus pandemic for now.

But it’s a mission that, if it comes off, could offer insight into the reasons behind the corals’ resilience and a glimpse into their future. “When you move south in the Red Sea, you’re essentially sailing into the future in terms of coral resilience to climate change,” Meibom says, “everything gets warmer and warmer.”

Meibom believes that intelligent sampling and genetic analysis of key coral species in the Red Sea, alongside understanding the environmental conditions they live under, could lead to a new way of thinking about how reefs work – including how they are connected. One key question is how corals act as “source” and “sink” regions in terms of creating and receiving coral offspring.

Identifying source regions can help guide reef management or remediation efforts in the region. And, as Grottoli says about her own coral reef and climate research, it’s important to try to understand the underlying traits that drive resilience in corals to make better-informed decisions on management, conservation and restoration.

The expedition would require funding, in addition to research permits from the majority of countries that border the Red Sea: Djibouti, Egypt, Eritrea, Israel, Jordan, Saudi Arabia, Sudan and Yemen. The region doesn’t exactly have a strong record of collaboration, and some of the Red Sea countries do not have diplomatic relations with one another. What they do have is a common interest in corals, whether or not they all realise it yet; if the reef is harmed, so too are the ecosystems and economies that depend on it.

“Looking into the future, this is really the livelihood of people of the Red Sea. I consider myself as one,” says Fine, a native of Israel. “Here there’s an amazing opportunity to prepare reefs for climate change, to allow them to persist and flourish. This is something that doesn’t exist in other regions.”

Sara Cannon, a doctoral candidate at the University of British Columbia’s Department of Geography and the Institute for Oceans and Fisheries, believes the Red Sea corals could indeed have the potential to help other corals. “By understanding what makes these corals more resilient, scientists could possibly help corals in other places adapt, using a process called assisted evolution,” she says. Cannon’s research is focused on attempting to understand ways that local and global human impacts interact to influence coral reef health and resilience in the central Pacific Islands. The Red Sea could provide information to help scientists to save reefs in other parts of the world that have not had the same opportunity to adapt, she says.

“And, the sad truth is that even if we could magically stop all greenhouse gas emissions immediately, global temperatures and carbon dioxide will remain high for centuries,” says Cannon. “To save reefs, we need to stop climate change, but we also need to consider how we can help corals adapt given that some effects of climate change have already become unavoidable. Corals in the Red Sea could be invaluable in that research.”

Bringing the planned expedition to fruition will require some skilled scientific diplomacy. So, together with the Swiss foreign ministry, Meibom and Fine helped create The Transnational Red Sea Centre (TRSC) in 2019. There has already been global interest in the organisation. “At the diplomacy level, we have ambassadors worldwide visiting and expressing support,” Fine says.

Cannonfeels the TRSC is on the right track. “There is a lot we don’t understand about how climate change interacts with local stressors to impact coral reefs, and we’re still learning how best to measure different responses to stress on coral reefs,” she says. “A group like the researchers who come together at the TRSC – especially one that prioritises diverse local voices – is integral to solving complex problems like threats to coral reefs, and to finding novel ways to save them.”

As soon as the TRSC can secure sufficient funding and permits, Meibom and Fine plan to set sail. Originally slated for this summer, the expedition is likely to be delayed by the ongoing coronavirus pandemic. When the yacht does set sail, it will begin the first leg of the expedition in Jordanian waters at the northern tip of the Gulf of Aqaba.

Coronavirus aside, it’s too soon to predict whether it will be smooth sailing or rough waters ahead. Fine and Meibom are optimistic that people across the region can put their politics aside and band together to protect the Red Sea reefs. “Reefs recognise no political borders,” Fine says. “What happens in one reef will affect the rest of the reef on the other side of the border.”

Politically and scientifically, there is a lot riding on this expedition. “This is probably our last chance [globally] at saving a major reef ecosystem that could be well-functioning 50, 60, 100 years from now,” Meibom says. “It’s a treasure. And it has enormous impacts on the region. So everybody has a common interest in preserving it – not only in the Red Sea, but for humanity.”, 9 April 2020