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Helping coral reefs adapt to a warming ocean

Stanford researchers are searching for heat-resistant corals that could ensure the survival of vulnerable reefs.

A view of the Rock Islands in the Republic of Palau, an island nation in the western Pacific Ocean. Image credit: Brendan Cornwell

Rising ocean temperatures are killing off coral reefs worldwide. Stanford coral geneticist Steve Palumbi wants to help save them – with a little help from evolution.

Some corals are more resilient to heat waves than others. Palumbi, a professor of Oceans at the Stanford Doerr School of Sustainability, along with his lab group have developed a low-cost way to test corals’ resistance to heat. The approach could help scientists understand the genomic drivers of coral heat resistance, opening the door to saving and restoring vulnerable reefs.

With start-up funding from a Big Ideas for Oceans grant awarded by the Stanford Oceans Department and the Stanford Woods Institute for the Environment, Palumbi is collaborating with researchers at Woods Hole Oceanographic Institute, The Nature Conservancy, Marshall Islands Conservation Society, and the Palau International Coral Reef Center to help put the lab’s new methods into practice in coastal communities.

A cream-colored branched coral on the ocean floor
A coral (Acropora digitifera) sits on a Palauan reef. Image credit: Brendan Cornwell

“Previously, people would go in after a major bleaching event and say, well, these corals are alive – they must be more resistant to bleaching,” said Palumbi, who is also a professor of biology in the Stanford School of Humanities and Sciences. “And that's fine, but you have to have a tragedy before you can find that out.”

Coral are made up of thousands of small, anemone-like animals called polyps, which typically live in warm, shallow waters. They secrete their own calcium carbonate exoskeletons, which together make up the structure of a reef. The polyps also host microscopic algae in their soft tissues, which they supply with ingredients needed for photosynthesis. In turn, the algae provide the polyps with sugar and oxygen in a mutually beneficial, or symbiotic, relationship. Coral bleaching happens when coral polyps expel the algae, a process that fades the reef’s distinctive colors and eventually causes the polyps to perish.

Three people in snorkeling gear sit discuss scientific notes on a boat.
Brendan Cornwell, a postdoctoral scholar at Hopkins Marine Station, discusses notes on a coral retrieval session with Stanford parents Michael and Carol Marusich. Image credit: Steve Palumbi

Palumbi and his lab group recently traveled to the Republic of Palau, an island nation in the western Pacific Ocean. Working with Stanford alumni who traveled to Palau on a university-organized trip, the researchers collected coral samples, then brought them back to the Palau International Coral Reef Center. Once in the lab, the team put the coral pieces into small tanks and raised the water temperature to mimic ocean warming. They then visually assessed the corals for signs of bleaching. This approach lets scientists quickly test small pieces of coral for heat resistance to identify coral and algae pairings that do well in warmer oceans. The new knowledge should help local collaborators and conservation groups grow and transplant more resilient corals to vulnerable reefs.

Typically, the specialized tanks and equipment to test corals for heat resistance can cost thousands of dollars, but Palumbi and his team have been working to modify low-cost and readily available tools for the experiments and training local researchers to perform them independently. “The idea of this protocol is basically that anybody can do it anywhere,” said Brendan Cornwell, a postdoctoral scholar at Hopkins Marine Station. “The lab’s goal at the moment is expanding the research to lots of different locations, and putting these tools in the hands of people who want to know something about the reefs where they live.”

These experiments also help Palumbi and his lab identify the underlying mechanisms of coral resistance to heat. The team previously sequenced the genomes of hundreds of corals. Now, the researchers are gaining a deeper understanding of heat resistance by comparing the genomes of each coral along with the genome of its symbiotic algae.

Knowing how both genomes interact gives us much much more power to explain the variation in heat resistance that we see.

Steve Palumbi Professor of Oceans

A large part of Palumbi’s work focuses on community engagement. While in Palau, he met with Sharp Sakuma, the governor of the Palauan state of Ngaraard, who is hoping to use Palumbi’s findings in a local reef restoration project. Researchers from the team also appeared on local radio and television broadcasts to discuss their work with staff members from the Palau International Coral Reef Center.

Palumbi’s lab also studies coral heat resistance in Belize and the Marshall Islands, and plans to do so in Maui and Indonesia. Together with local collaborators, Palumbi and his lab group aim to identify heat-resistant corals and build more resilient reefs. This work is also supported by follow-up funding from Stanford alumnus Dan Chung, '84.

“The big idea is that evolution has crafted a solution to help corals in the future,” said Palumbi. “It’s done, it’s built, it’s sitting there, and we need to learn how to use it.”

Palumbi is the Jane and Marshall Steel Jr. Professor of Marine Sciences, a professor of biology at the Stanford School of Humanities and Sciences, and a senior fellow at the Stanford Woods Institute for the Environment. The Stanford Oceans Department and Woods Institute for the Environment are both housed at the Stanford Doerr School of Sustainability. Palumbi is also a faculty leader for Stanford Travel/Study, an educational travel program available to Stanford alumni and friends of the university.


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