Bleaching events have stressed coral worldwide, particularly the Great Barrier Reef, and research says their survival depends on quickly slowing climate change.
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| The Great Barrier Reef has experienced a series of damaging bleaching events since 2014. Credit: Getty Images |
Two doses of bad news for the world's coral reefs came in the last week. First, Australia's government confirmed that the Great Barrier Reef
is in the midst of a second consecutive year of mass bleaching. It's
the first time the reef has experienced back-to-back events, and it
seems to be weakening many of the corals.
Then
on Wednesday, leading scientists published a new study about last
year's bleaching—the worst to date—suggesting that when the seas are hot
enough for long enough, nothing can protect coral reefs. Their only
hope is that we rapidly slow climate change.
The research, published in the journal Nature,
looked at data from three bleaching events along the 1,400 mile-long
Australian reef system dating back to 1998. By looking at factors
including water temperature, water quality and fishing protections, the
authors determined that last year's bleaching was linked almost
exclusively to ocean warming.
Conservationists
have long hoped that protecting corals from other threats, such as
pollution and overfishing, might help shield at least some of them from
bleaching, too. While the new paper doesn't entirely deflate that
hope—such protections likely help reefs recover—it shows that such work
provides little if any relief from severe bleaching.
"At
the level of heat stress that was seen during this event, it just
didn't matter," said C. Mark Eakin, coordinator of the Coral Reef Watch
program at NOAA and a co-author of the paper.
Ilsa
B. Kuffner, a marine biologist with the United States Geological Survey
who was not involved in the research, said the new paper supports a
solid body of evidence suggesting that disease and bleaching are driving
coral mortality, while other factors play a more important role in the
recovery from those threats. "It's a distinction that, while it's
subtle, is also very important when you talk about what's actually
causing coral reef decline," she said.
The
paper also found that a reef's history made little difference. Some
studies have suggested that previous bleaching may make reefs more
resilient if they are given time to recover, perhaps by killing off
weaker corals or driving some adaptive response.
Warmer-than-average
temperatures can cause coral to expel the symbiotic algae that live on
its surface, turning the reef white. Such bleaching stresses coral and
can make it more susceptible to disease and death.
The
world's reefs are in the midst of what scientists consider to be a
single, mass bleaching event dating back to 2014. Climate models project
that most of the world's reefs could experience annual bleaching by 2050 without rapid cuts in greenhouse gas emissions.
While coral can survive even extreme bleaching, surveys conducted this month
along the Great Barrier Reef are showing evidence that successive hits
take a toll. Eakin said the level of heat stress—a measurement of how
hot the waters are for how long—is lower than last year, and yet the
bleaching appears to be just as widespread.
"They
haven't bounced back yet, so when you hit them with another event a
year later, you can see more bleaching at a lower level of heat stress,"
he said. "A lot of the corals that have survived last year really are
not ready for another event."
The bleaching has also spread to areas of the reef that escaped last year's event, according to the recent surveys.
Successive
bleaching also appears to be reshaping the makeup of the reef system.
Reefs are composed of a rich diversity of coral species, with some
particularly sensitive to bleaching and some that recover much more
quickly than others. With consecutive years of bleaching, and after four
events over 20 years, the new paper said the composition of the reef is
changing in areas that have seen recurrent bleaching, perhaps
irreversibly.
"The
good news is you've got some tough corals that are surviving," Eakin
said. "The bad news is, one of the most important things about coral
reefs is their diversity, and you're cutting out some of that
diversity."
The paper's authors believe that protecting reefs from
pollution and overfishing will help them recover from bleaching. But the
most important action, they said, lies elsewhere.
Links
- As Coral Reefs Continue to Struggle in Warming Oceans, a Group Forms to Save Them
- As Coral Bleaching Goes Global, Scientists Fear Worst Is Yet to Come
- Arctic Sea Ice Melt, Driven by Global Warming, Accelerated by Nature
- Chief Environmental Justice Official at EPA Resigns, With Plea to Pruitt to Protect Vulnerable Communities
- Exxon Concealed Tillerson's 'Alias' Emails From NY Climate Fraud Probe, AG Claims
- Scientists Call Out Pruitt's False View of Climate Change
- Massive Permafrost Thaw Documented in Canada, Portends Huge Carbon Release
- Rate of Ocean Warming Has Nearly Doubled Over Two Decades, Study Says
- What Slashing the EPA's Budget by One-Quarter Would Really Mean
- Cook Inlet Gas Leak Remains Unmonitored as Danger to Marine Life Is Feared
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