The Rock Islands of Palau, a tiny nation in the Pacific located midway between the Philippines and Papua New Guinea, look like most people’s definition of paradise. Several hundred lush green islands rise above shallow lagoons in a mini archipelago spread across 41 square kilometers (16 square miles) just south of the main island.
For the biologists who flock to the Micronesian nation, the real draw is the Rock Islands’ pristine coral reefs, found both in the shallow waters of protected lagoons and fringing the deeper waters offshore. Palau has long been a hot spot for coral research, and now, in a study recently published in Communications Biology, scientists reported finding that some corals there can tolerate temperatures far warmer than researchers realized. The discovery could provide hope for reefs around the world threatened by warming ocean waters. Pressure Gauges
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The fate of coral reefs has become one of the most notable bellwethers of climate change, as hotter and more acidic oceans imperil these vibrant ecosystems. But along with rising tones of alarm, scientists are also finding reasons to be hopeful. As marine biologists have taken a closer look at thousands of coral species around the world, they’ve noticed that some fare surprisingly well when waters are abnormally warm.
“Corals all over the world are dying in heat waves,” said Stephen Palumbi, a professor of biology in the oceans department at Stanford University, who was not involved in the study. “But wherever you see that happening, almost all of the time, there are [also] corals that are not dying in heat waves.”
In Palau, the Rock Islands provide a perfect natural laboratory to study those disparate responses. Reefs found in the shallow lagoons between islands are about 1.5°C warmer than the nearby reefs surrounding the islands. It’s an ideal way to fast-forward to a future made hotter by climate change, said Hanny Rivera, who coauthored the recent study as a postdoctoral researcher with the Massachusetts Institute of Technology–Woods Hole Oceanographic Institution Joint Program.
“You have organisms that are living right now in conditions that we expect to see in the open ocean in 50 or 100 years.”
“You have organisms that are living right now in conditions that we expect to see in the open ocean in 50 or 100 years,” she said.
Along with her coauthors, Rivera analyzed genetic material from Porites lobata corals from both the warm lagoons and the cooler outer reefs. The researchers paired that with core samples that showed them how the coral had responded to conditions in the past. Like trees, corals grow a little bit each year, leaving a record of their growth in layers inside their skeletons. Light bands in a coral core sample represent periods of extreme stress and often correspond to bleaching events.
Using the core samples, the researchers found that some lobata corals fared far better than others during abnormally hot years. During the 1997–1998 El Niño, which caused mass bleaching events around the world, 60% of the corals in Palau’s outer reefs bleached. But inside the lagoons, where temperatures were even hotter, just 25% of the corals bleached. The researchers saw the same pattern repeat in other extremely warm years: The Rock Islands lobata corals bleached at far lower rates.
“That suggests that the Rock Islands environments have in some ways been selecting for organisms that can tolerate higher temperatures,” Rivera said.
Backing up that hypothesis, the researchers found clear differences between the genomes of the corals that bleached and those that didn’t. In fact, Rivera’s work turned up not one, but four distinct lineages of lobata corals in Palau, with some more prevalent inside the lagoons and some more prevalent in the open ocean.
One lineage in particular turned up only in the Rock Islands’ lagoons, and it possesses a combination of traits—heat tolerance and speedy growth—that could make it particularly well suited for future reef restoration, Rivera said.
The work is offering a hopeful sign for the future of corals around the world, said Mikhail Matz, a coral scientist at the University of Texas at Austin who was not involved in the study.
“[Some] corals can, and probably will, at least for a while, be able to adapt to the increasing threat of climate change,” he said.
“There are really important habitats that need to be protected.”
The challenge for scientists is discovering those corals now, before it is too late for other reefs. Coral restoration projects that select and propagate the most heat resistant corals might future-proof reefs around the world. But it’s far too soon to claim victory for corals, Rivera said. Other dangers, such as pollution and human interference, still threaten the fragile environments that many unprotected reefs reside in.
“There are really important habitats that need to be protected,” she said.
Palau has been ahead of its time in protecting its underwater natural resources for the future. Now we need to apply that model elsewhere as we search for more of the corals that can survive heat waves, Palumbi argued.
“Giving people the tools to do that in as many parts of the reef world as possible is our way of trying to make that bad future of corals you are thinking about as far away as possible.”
—Nathaniel Scharping (@nathanielscharp), Science Writer
6 February 2023: This story has been updated to correct the journal name and clarify coral color banding.
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