How Coral Reefs Survive in the Hottest Sea on Earth

Close-up of a coral reef in the Arabian Gulf near Abu Dhabi.

Genetic Science Offers New Clues

The Arabian region contains some of the most unique but understudied coral reef ecosystems on Earth. Corals in the Arabian Gulf survive extreme sea temperatures — 36 degrees Celsius or higher in the summer — and are more heat tolerant than any other corals on the planet.

Few studies, however, have explored the molecular mechanisms that allow them to persist in such harsh conditions. NYU Abu Dhabi researchers are turning to genetics to find answers.

A new comparative study of corals from the Arabian Gulf and the neighboring Gulf of Oman, a much cooler body of water, is one of few that has examined genetics of both corals and their natural symbionts, an algae that live inside coral tissue.

The algae is hugely important, the scientists said, because corals get more than 90 percent of their energy from it. In science, the mutually beneficial relationship between corals and algae is known as symbiosis: an interconnectedness of two living organisms.

“By looking at both corals and algae, we can get a better idea of whether one or both are involved in Gulf coral thermal tolerance,” said Edward Smith, postdoctoral associate researcher at NYU Abu Dhabi, and also determine if there’s any exchange of genes between reefs around the region.

Diving for DNA

DNA analysis was performed on corals collected from reefs in the Arabian Gulf near Abu Dhabi and from sites in the Gulf of Oman around Fujairah and Muscat — where average sea temperature is nearly five degrees cooler than the Arabian Gulf: 31.5 degrees Celsius in the summer. The reefs are separated from each other only by the narrow Strait of Hormuz at the entrance of the Gulf.

The scientists used genetic markers, sequences of DNA, to examine both individual corals and groups of corals, and discovered some key differences, Smith said, namely that Arabian Gulf corals and their algae partners are genetically distinct from their counterparts in the cooler Gulf of Oman.

Limited gene flow exchange between regions indicates that Arabian Gulf corals have adapted to cope with their extreme conditions, which is “interesting because the results suggest that both the coral and their algae together contribute to the superior thermal tolerance traits of Arabian Gulf corals,” Smith said.


Genetically adapted populations of corals and their symbionts in the Arabian Gulf will provide new insight into whether corals elsewhere in the world will be able to cope with climate change.

Ed Smith, postdoctoral researcher

Genetically adapted populations of corals and their symbionts in the Arabian Gulf are an important scientific resource, he added, “that will help us understand the mechanisms involved in coral thermal adaptation, and provide new insight into whether corals elsewhere in the world will be able to cope with climate change.”

Regional adaptation also leads the researchers to conclude that reefs threatened by climate change in the Gulf of Oman or Indian Ocean are unlikely to acquire the so-called ‘super genes’ of Arabian Gulf corals.

Arabian Gulf reefs are the most diverse ecosystems in the region and support major economic areas such as fisheries. Unfortunately, said John Burt, NYUAD associate professor of biology, the conditions that have made Arabian Gulf corals among the hardiest known to science also makes them vulnerable: they are living in very stressful conditions, and any further stress can push them over the edge.

“In the past three decades we’ve witnessed widespread degradation of reefs around the region, with sedimentation from coastal development and nearshore reclamation being the prime culprits,” Burt explained. “If we are to conserve these scientifically and economically important natural assets, management efforts to limit human stressors are critical.”

The research results were published in scientific journal PLOS One.