Coral Reef Resiliency Gives Scientists Some Hope After Back-to-back Marine Heat Waves

A bit of good news about the health of Earth's highly sensitive coral reefs: Some are more resilient than others, at least in Australia's Great Barrier Reef.

After a 2016 marine heat wave destroyed or severely damaged corals in the Great Barrier Reef, a period of extreme warmth a year later revealed to scientists that the survivor corals had adapted to the higher temperatures. Their findings were published in the journal Nature Climate Change, detailing how extreme climate change affects such ecosystems.

In the 2016 event, bleaching occurred in which the bright colors of the coral faded because of the warmer waters. Scientists said there was reason to hope that coral might be able to resist the warming effects, as it took longer in 2017 for the coral to bleach under similar conditions.

Terry Hughes, coral reefs expert at James Cook University in Australia and lead author of the study, characterized the survivor corals as robust. "It's one enormous natural selection event," Hughes told The New York Times.

The study points to "the emergence of ecological memory" during the "unprecedented back-to-back mass bleaching" of the Great Barrier Reef, first in 2016, then again in 2017.

The study described the incident as a "climate-driven event" within a sequence or pattern of such events. Study scientists acknowledged the accelerating pace of climate change and its cumulative effect on such vulnerable ecosystems.

"Despite the fact that Year 2 was hotter, we saw less bleaching over all across the whole reef," Hughes told The Times. This was attributed to "ecological memory," the idea that the past experience of a biological community can influence its ecological response today or in the future.

The water temperature increased between seven and 14 degrees Fahrenheit in 2016, bleaching sections of the reef. But a year later, it took a longer time for the recurrent warmer water to bleach coral to the same extent.

The last time bleaching negatively affected the health of the coral was in separate events in 1998 and 2002, The Times reported. Coral reefs may support a quarter of all ocean life. The Great Barrier Reef corals stretch over 1,430 miles.

The back-to-back sequence of bleaching most recently concerned scientists because it denoted a pattern. Normally, it takes 10 years for coral to recover.

In November, a National Academies of Sciences, Engineering, and Medicine report concluded that human intervention is needed to help preserve the world's coral reefs.