Egypt's climate-resistant 'super corals' are feeling the heat

Scientists can't agree why Red Sea reefs have been immune to bleaching for so long. The answer could be the key to saving these hardy corals as climate change begins to take its toll.

As coral reefs around the world have experienced massive bleaching events, Egypt's Red Sea corals have raised hopes. They have been unusually resilient to rising water temperatures, and if oceans continue to warm, some scientists even predict that Egypt's northern reefs could be the world's last remaining coral reefs.

This is what Mahmoud Hanafi, a professor of marine biology at Suez Canal University and a consultant to the Hurghada Environmental Protection and Conservation Association (HEPCA), had already predicted. But in the summers of 2023 and 2024, heat waves stressed the coral ecosystems of the Red Sea. A HEPCA review led by Hanafi found that by 2024, coral bleaching across the Red Sea would occur. In northern areas, less than a tenth of the coral colonies were surveyed, but in the south, bleaching killed half of the corals.

Scientists are racing to piece together what these events mean for the reefs, long described as "supercorals" because of their incredible hardness. But the question now is not how much heat they can withstand, but what has protected them until recently — and whether that protection will last.

In very warm waters, the algae living among the coral polyps begin to produce toxins. As a defense mechanism, the corals expel the algae. This is what is referred to as coral bleaching, and since these microscopic organisms are the main source of food for corals, bleaching events starve corals.

This is one of the other negative effects that warmer seas can have on corals, which is problematic not only for corals, but for all other reef life. According to the United Nations Environment Programme, reefs cover less than 1 percent of the seafloor, but support at least 25 percent of marine species—some of which have only just been discovered.

For many years, the reefs of the northern Red Sea remained fairly stable as temperatures rose, while other coral ecosystems suffered bleaching. Islam Osman, a marine ecologist at the King Abdullah University of Science and Technology (KAUST), points to the evolutionary history of Egyptian corals as a possible explanation for the heat tolerance.

It is believed that the corals spread to the Red Sea through the Bab al-Mandeb Strait, which is located at the southern point of the sea between Djibouti and Yemen today. Osman believes that passing through these especially warm waters acts like a natural filter. Heat-tolerant species and genotypes survived and their descendants spread northward into colder waters.

However, resilience varies across the region, which is why Hanafi is not convinced that evolutionary history is the primary explanation for the resilience of Egyptian rocks. He puts more emphasis on water circulation

The northern Red Sea is experiencing a current reversal. This can create vertical mixing that brings cooler water from below to the surface, he explains. These conditions can protect corals from heat, even when the surrounding air temperature remains high.

The distinction is important. The survival of these reefs may not have much to do with the biology of corals or their symbiotic algae, which may explain why Red Sea corals began to bleach in 2024.

The sea remained unusually calm for about a month and a half during the 2024 heat wave, undermining the circulation that he believes normally helps protect the reef. The HEPCA report identifies poor water circulation as a contributing factor to bleaching. Exceptional high tides in July 2024 may also exacerbate stress on shallow coral communities.

Osman admits that calmer seas could have made the bleaching more intense, but says that explaining circulation needs more research. "I don't deny this possibility," he says. But what I am saying is that the temperature was the main issue.

These two explanations are not necessarily mutually exclusive. But understanding their relative importance can help scientists assess the vulnerability of these reefs to future heat waves.

There are signs of improvement. Initial estimates from HEPCA one year after a bleaching event put recovery rates between 75 and 88 percent, depending on the species and location. That's a much stronger comeback than elsewhere in the world, where many reefs are just starting to recover — if at all.

Work is also underway to protect Red Sea reefs before the next heat wave, with the Egyptian government establishing new protected areas as well as partnerships with the United Nations Development Program and the Global Coral Reef Fund on conservation and sustainable management.

Osman sees such initiatives as a positive step, but stresses that conservation needs continued support. "We definitely need more sustainable funding because conservation is not a one-year event."

For Hanafi, the future of Egypt's reefs depends on whether climate change alters the circulation that likely kept the corals alive.

Whatever explains their unusual resilience, local conservation cannot stop ocean warming. "So, the key is to reduce carbon dioxide and greenhouse gases. Any other solution just takes time," Hanafi adds.

This story originally appeared on WIRED Middle East.