Coral Reefs are Bleaching Every Six Years

As reported in the Washington Post, among other news outlets, a sobering study suggests that coral reefs are bleaching every six years — four to five times faster than they did in the 1980s. The study further suggests that this rate is far too rapid for reefs to ever recover.

"With a fourfold increase over the last 35 years, if you take that forward, it's unfortunately in complete agreement with what the climate models have been saying," Mark Eakin, one of the study's authors and head of the National Oceanic and Atmospheric Administration's Coral Reef Watch told the Post.

"[We're] looking at 90 percent of reefs seeing the heat stress that causes severe bleaching on an annual basis by mid-century."

As most divers know, coral expels its symbiotic algae (which gives it color) when it becomes stressed due to environmental pressures. Once the colorful alga disappears, the coral appears "bleached," a white skeleton and shadow of its former self. The longer it remains without its protective algae, the higher the chance it will remain bleached and eventually die. Because of this, scientists have distinguished between moderate and severe bleaching. Coral can often recover from the former; not so the latter.

Mass bleaching event

This latest bit of bad news follows on the heels of the worldwide global bleaching event from 2014 to 2017 that claimed as a casualty much of the Great Barrier Reef. This new survey, published in Science magazine, catalogued 100 major coral reefs from 1980 through 2016 and found only a few that had not suffered from severe bleaching. Even more worrisome, the rate of severe bleaching has increased over time, to once every six years. In the 1980s, reefs routinely bleached only once every 25 to 30 years. To blame are increasing ocean-water temperatures, present year-round now and not only in warm-water El Nino years. Many other stressors contribute as well, including overfishing, which leads to an abundance of algae on an already struggling reef.

This astonishing difference has occurred with a change of only 1.8 degrees F (1 C) of global warming so far, making clear the threat that faces the world's remaining coral reefs if we do nothing to reverse the trend. The speed of the bleaching has surprised even the scientists who study it.

"It did in some ways even sneak up on scientists," Eakin told the Washington Post of the 2014-2017 bleaching event. "I wasn't expecting to see a multiyear bleaching event for another decade. It is happening faster than even those of us who are well attuned to it are expecting. It wasn't beyond what we thought was possible; we were just being hopeful."

Can reefs recover?

Although analysis of the 2014 to 2017 event is ongoing, it affected 75 percent of the world's reefs, including gigantic portions of the Great Barrier Reef. Based on the rate of damage, scientists worry that reefs do not have adequate time between bleaching events to recover. It takes 10 to 15 years for the quickest-growing corals to bounce back, and even longer for other essential reef-building species. Many reef systems are increasingly relying on help from human beings (who ironically are responsible for the problem in the first place) to help regenerate. But it still may not be enough. "There's some things you don't have time to change," said Eakin in closing to the Washington Post.

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