This evolutionary gift may protect corals from climate change

To see what defenses corals are already developing against warmer waters, Meibom and colleagues wanted to find out how much heat the coral reefs and their complex network, called hoolobiont, could withstand. He likens it to testing the strength of a rubber band: How tight can you stretch it before it breaks? How long does it take to return to its normal shape?

It is crucial to understand how these corals function at the cellular level, says Karen Kleinhouse, who researches corals at Stony Brook University. “These amazing coral reefs will be among the last to survive” until the end of the 21st century, she says. “We need to know what they’re doing, what’s going on, and how they’re doing it.”

In their experience, the researchers grew S. pistillata In a series of aquatic creatures they named the Red Sea Simulator. Each aquarium can be customized to replicate specific water conditions and to expose corals, algae and bacteria to different temperatures for different periods of time. Then the researchers examined the genes that the corals expressed during their natural state, how that changed with the increase in temperature, and how quickly the gene activity returned to normal when the temperature decreased.

They found that the three organisms were all able to alter the genes they used while heating the water. For example, corals have shown the use of genes that are involved in the unfolded protein response, a mechanism used to detect environmental stress and Maintain balance In the cell in other studies, it has been described as coral First line of defense Against heat. Meanwhile, the algae refused to activate genes related to photosynthesis. In general, the Red Sea species were able to survive until the temperature rose by more than 5 degrees Celsius, and once the scientists lowered the temperature in the reservoirs, the entire holobiont returned to its normal state, even after a week under hot conditions. . Meibom likens their flexibility to an ultra-fit athlete able to recover quickly after a major workout and prepare for another challenge.

“The paper is a really good job and sheds light on the early stages of the response to heat stress in heat-resistant corals,” says Andrea Grottoli, a professor at Ohio State University’s School of Geosciences who studies corals and climate change. Note that there are some limitations to this approach. Just because the gene is activated does not mean that the coral will eventually produce new proteins. It’s an indication that corals are responding to their environment, but it’s not the whole story – you also want to know exactly what biochemical changes they have been making to adapt, and how these corals are changing physically.

Grottoli also notes that the study’s longest exposures, of up to seven days, are shorter than many true heat waves. “Most natural whitening events take two months,” she says.

Meibom agrees that his study does not explain how these newly activated genes could help corals survive, but he says that getting to know them is a step toward figuring it out. “It provides a hint of what is happening.”

It is also unclear why these corals have this heat resistance but some do not. It might not be because it evolved in the hot climate of the Red Sea, but because it arrived from a hotter place. Meibom believes it may have something to do with the species that inhabited the Red Sea during the last Ice Age, about 20,000 years ago. The water evaporated from around the equator and eventually froze into large glaciers. With all that water trapped in the ice, sea levels have plummeted, cutting the Red Sea off the Arabian Sea, essentially turning it into a lake. The water level decreased and the accumulation of salt made it an inhospitable environment. But when the glaciers melted and the connection to the rest of the ocean was repaired, water and new life forms poured in. This included the coral that lives in the Arabian Sea, which slowly made its way out of the hotter southern waters. Only these species that were adapted to the heat were healthy enough to send their larvae north to repopulate the Gulf of Aqaba. They were chosen.

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