Repetitive, severe marine heat waves are disrupting the Great Barrier Reef's ability to regrow with a similar abundance and mix of species as before, a new study warns. The paper, published in Nature Wednesday, depicts a vast, complex reef ecosystem that is on the verge of "ecological collapse."
Why it matters: The Great Barrier Reef is the word's largest coral reef ecosystem, spanning 1,400 miles from north to south off the eastern coast of Australia. The new results add to a series of grim findings about just how vulnerable this reef community, long viewed as too big to fail.
- The new findings also raise the provocative question of what healthy coral reefs will look like in the future, if they exist at all, as ocean waters continue to heat up from human-caused global warming.
What they did: For the study, researchers at Australia's Center 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 out on the Great Barrier Reef.
- Researchers compared spawning behavior in years prior to the marine heat waves that struck two-thirds of the reef in 2016 and 2017 against what happened immediately following the heat waves. Such heat waves are also known as coral bleaching events for their tendency to turn corals a ghostly white as heat stress causes organisms to kick out symbiotic algae that lends corals their vibrant colors.
- The study found that such heat events compromise the reef's capacity to recover by causing a sharp plunge in reproduction rates.
- By killing adult corals, the heat waves slashed the rate of reproduction and skewed the balance between coral species.
- According to the study, the number of new corals settling on the Great Barrier Reef declined by 89% following the assault on adult corals in 2016 and 2017.
- One species, Acropora, which establishes branching and table coral, declined by 93% compared to prior, non-heat wave years.
What they're saying: The increased frequency of bleaching events means that more corals could perish before they can recover.
"One more 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, of James Cook University in Australia, tells Axios via email.
- But the new study is just one snapshot of the reef's damage right after a massive shock.
But, but, but: Severe coral bleaching events mean that the surviving corals may be more heat-tolerant and could survive future events, if they're allowed to mature first.
Madhavi Colton, program director with the nonprofit Coral Reef Alliance, says she's eager to see what happens with coral recruitment (the process by which coral larvae attach themselves to existing coral) beyond just a single year after the bleaching events.
- “I would be interested in seeing if this trend holds up, then we should be more alarmed than we are with one very bad year,” she tells Axios.
The bottom line: According to Kim Cobb, a climate scientist and coral expert at Georgia Tech, the future of the world's reef ecosystems will look nothing like what we've known. “Will they ever get back to where they were before these events happened? Probably not," she says.
"Will they look very, very different? Will there just be a different kind of reef there, will they have a different functionality? Maybe yes.” She added, though, that the outlook for the world's reefs is "pretty bleak."