Marine scientists have made an early but exciting discovery about how some corals respond to stress.
Certain species of corals can activate a set of ancient, defensive genes when exposed to high water temperatures, ocean acidity or low oxygen levels, a team from Stanford University found in a new study.
This genetic response suggests these corals are particularly tolerant to changes in the ocean — a trait that could be key to their survival as the oceans heat up and turn more acidic because of human-driven climate change.
The stress-triggered genes may also serve as a warning sign for scientists that a coral bleaching event is about to happen, the researchers said in a paper published Wednesday in the journal Science Advances.
Coral reefs are among the most diverse ecosystems on Earth, providing shelter and sustenance to everything from algae, worms and snails to thousands of fish species and shellfish. They also bring billions of dollars’ worth of goods and services to land dwellers through tourism and fishing.
Yet corals are facing an unprecedented threat from global warming, which is raising water temperatures worldwide.
In 2015 and 2016, Australia’s iconic Great Barrier Reef suffered its largest die-off ever recorded due to unusually warm waters, with an average of 67 percent of corals in one area declared dead. The corals had expelled the symbiotic algae that give them their vibrant colors, creating hundreds of miles of stark-white coral. This phenomenon is known as coral bleaching, and the longest-recorded worldwide bleaching event is still underway.
The corals in the Stanford study aren’t necessarily immune to these threats. But researchers said their stress response indicates they may be less vulnerable than other types of coral, giving them more time to adapt.
“It shows we can predict areas in the world where there are corals that are more likely to be more tolerant to future climate scenarios,” said Lupita Ruiz-Jones, a co-author of Wednesday’s study and a lecturer at Stanford.
This knowledge could help conservationists focus their efforts on less heat-tolerant species first, she said.
For the study, Ruiz-Jones and Stanford marine sciences professor Steve Palumbi monitored three coral colonies in a lagoon on Ofu Island, American Samoa. During the course of 17 days in August 2013, they monitored over 17,000 coral genes just after 12 p.m. each day.
On days 7 and 8, when tides were lowest and water temperatures spiked above 30.5 degrees Celsius, or 87 degrees Fahrenheit, the corals’ genes turned on a set of defensive genes involved in the “unfolded protein response.” The response is used by all mammals — including humans with diabetes or cancer — to help cells combat problematic proteins.
“They started using a whole set of genes that they had just not been using before,” Palumbi said in a press release. But by day 9, when the tides rose and water temperatures cooled, the corals no longer tapped into this genetic stress response.
“It’s the first time to detect a coral stress response in the field when there’s no visible signs of stress,” Ruiz-Jones said.
The scientists said the corals’ frequent, relatively brief exposure to high temperatures might ultimately make them more resilient — just as regularly lifting weights or running keeps you ready for a race. By studying other heat-tolerant corals, marine biologists globally could start to identify and map other tougher colonies around the world, the researchers said.
“There is resiliency growing into the system because of adaptation,” said Wade McGillis, a professor at Columbia University’s Lamont-Doherty Earth Observatory who studies coral heat stress and was not involved in the Stanford study.
“Most certainly, coral species with those gene types are going to have a better ability to handle the next [warming event] and keep going on,” he said by phone from the Galapagos Islands.
Recognizing that many coral reefs are likely to perish as ocean temperatures climb in coming years, conservationists are turning to strategies that target the more resilient species for saving.
For example, a new initiative known as 50 Reefs launched in late February. Led by Bloomberg Philanthropies, it aims to identify the 50 highest priority coral reefs that have the best chance of surviving climate change, as a way of protecting coral reefs from climate change-induced extinction.