To see what coral defenses are already developing against warmer waters, Meibom and his colleagues wanted to learn how much heat corals and their complex network, called holobiont, could withstand. It’s like trying the strength of a rubber band: How long can you stretch it before it breaks? And how long does it take to return to its regular form?
Karine Kleinhaus, who studies corals at Stony Brook University, says it is crucial to understand how these corals operate at the cellular level. “These wonderful corals will be among the last to survive” by the end of the 21st century, he says. “We need to understand what they do, what happens, how they do it.”
In their experiment, the researchers grew S. pistillata in a series of aquariums they have been called the Red Sea Simulator. Each aquarium could be customized to replicate specific water conditions and to expose coral, algae, and bacteria to different temperatures for different time periods. Next, researchers examined what genes the coral expressed during its normal state, how it changed when the temperature rose, and how quickly that gene activity returned to normal when the temperature was reduced.
They found that all three organisms were all able to change which genes they used while the water was heating up. The coral, for example, has discovered the use of genes that are involved in the response of the explained protein, a mechanism that is used to detect environmental stress and preserve homeostasis in the cell; in other studies, it has been described as ‘coral’. first line of defense against heat. Meanwhile, algae refused the activation of genes related to photosynthesis. In general, Red Sea species can stay alive until the temperature warms by more than 5 degrees C. And once scientists have lowered the temperature in the tanks, all the olobiont is back to a state normal, even after a week in hot conditions. . Meibom likens his resilience to a super-fit athlete who is able to recover quickly after a great workout and prepare for another challenge.
“The journal is really a good job and sheds light on the early stages of the thermal stress response in thermally tolerant corals,” says Andréa Grottoli, a professor in the School of Earth Sciences at State University. Ohio studying coral and climate change. But she notes that there are some limitations in this approach. Just because the genes are activated doesn’t mean the coral will eventually make new proteins. It’s an indicator that the coral is responding to its environment, but it’s not the whole story — you also want to know exactly what biochemical changes it makes to adapt, and how those physically change the coral.
Grottoli also notes that the longest exposures in the study, up to seven days, are shorter than many real-life heat waves. “Most natural whitening events last two months,” she says.
Meibom agrees that his study does not explain how these newly activated genes might help the coral survive, but says identifying them is a step toward understanding that. “It provides a suggestion for what happens.”
It is also unclear why these corals possess this heat resistance, but others do not. It may not be because they evolved in the warm climate of the Red Sea, but because they came from an even warmer place. Meibom theorizes that it may have to do with the species that populated the Red Sea during the last ice age, about 20,000 years ago. The water from around the equator evaporates and eventually freezes into large glaciers. With all that water trapped in the ice, the sea level has dropped, cutting the Red Sea off the Arabian Sea, essentially transforming it into a lake. The water level drops and salt accumulates, making it an inhospitable environment. But when the glaciers melted and the connection with the rest of the ocean was repaired, new water and life forms flooded. That included the coral that lives in the Arabian Sea, which had been slowly receding from its warmer 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 selected.” It’s like a filter, ”Meibom says.