On Monday, news broke that it happened again. For the second year in a row, warm ocean temperatures are bleaching the Great Barrier Reef. The white splotches of ocean floor indicative of the phenomenon run even farther south—some 500 kilometers—than they did last year. The bleaching occurred even though there is no worldwide El Niño this year: The reef is ailed not by a rare climatic phenomenon but by the baseline warming of the oceans.
Until this decade, back-to-back bleaching events like that simply didn’t happen.
“It’s new. It is so new. It’s a complete change in the phenomenon that all of us study,” said Ruth Gates, a professor at the Hawaii Institute of Marine Biology and the president of the International Society for Reef Studies. “We knew that this day would come—we’ve been seeing the thermal-tolerance threshold for corals get closer and closer, and we knew it was pushing over the limit for coral survival.”
The reef that Gates knows best—the coral reef in Kāne’ohe Bay, right next to the institute where she works—was one of the first in the world to suffer a back-to-back bleaching. In 2014, a warming Pacific pushed the Kāne’ohe Bay corals to warm; in 2015, the sea bleached them again. “We were not really expecting it to be a bleaching year then and we didn’t expect it to be a bleaching year the following year,” she told me.
Since then, she has been monitoring the health of the reef and watched it recover. Scientists still don’t know how repeated bleaching events—especially in back-to-back years—will affect the long-term health of a coral reef. Kāne’ohe Bay has recovered faster and more vigorously than Gates expected, but it is a considerably less biodiverse reef than the Great Barrier Reef. Much of Gates’ research focuses on expanding coral resilience between reefs. (There was a wonderful New Yorker profile on her work last year.)
“We are just one species that are in line to be hit very heavily by climate change,” said Gates. “Coral reefs are in the front line but they’re telling us something very important.”