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Axios Science – April 4, 2019



Repeated, severe marine heat waves interfere with the Great Barrier Reef's ability to regain with a similar abundance and mixture of species as before, warns a new study. The paper, published in Nature Wednesday, shows a large, complex reef ecosystem that borders on "ecological collapse".

Why is it important: The Great Barrier Reef is the word largest coral reef ecosystem that spans 1,400 miles from north to south off Australia's east coast. The new findings add to a number of nasty findings about how vulnerable this reef community, long seen as too big to fail.

  • The new results also raise the provocative question of what healthy coral reefs will look like in the future if they exist at all, as the sea waters continue to warm up from man-made global warming.

What they did: For the study, researchers at Australia's Centers of Excellence for Coral Reef Studies examined coral reproduction or spawning, rates from one year to the next by combining years of in situ measurements on the Great Barrier Reef.

  • Researchers compared spawning behavior this year prior to the marine heat waves that hit two-thirds of the reef in 2016 and 2017 against what happened immediately after the heat waves. Such heat waves are also known as coral bleaching events for their tendency to make the corals ghostly white, as hot stress causes organisms to kick symbiotic algae, giving corals their vivid colors.
  • The study found that such heat events compromise the reef's ability to recover by causing a sharp jump in reproduction rates.
  • By killing adult corals, the heat waves spread the reproduction speed and skewed the balance between coral species.
  • According to the study, the number of new corals on the Great Barrier Reef decreased by 89% after the attack on adult corals in 2016 and 2017.
  • One species, Acropora, which establishes branching and table coral, fell by 93% over earlier, non-heat wave year.

What they say: The increased frequency of bleaching events means that more corals can die before they can recover.

"A major large-scale bleaching event in the next few years and it could be curtains" for many parts of the Great Barrier Reef, study co-author Andrew Baird, from James Cook University in Australia, Axios tells via email.

  • But the new study is just a snapshot of the reef damage just after a massive shock.

But, but: Serious coral bleaching events mean that the surviving corals can be more heat-tolerant and can survive future events if allowed to mature first.

Madhavi Colton, program director with the nonprofit Coral Reef Alliance, says she is eager to see what happens to coral recruitment (the process of coral larvae attaching to existing corals) beyond just one year after bleaching events.

  • "I would be interested to see if this trend stops, we need to be more alarmed than we are in a very bad year," she tells Axios.

Bottom Line: According to Kim Cobb, a climate scientist and coral expert at Georgia Tech, the future of world reef ecosystems will not look like what we have known. "Will they ever come back to where they were before these events happened? Probably not," she says.

"Will they look very, very different? Will there just be another kind of reef there, they will have another functionality? Maybe yes." She added, however, that the prospect of world reefs is "pretty gloomy".

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