The unique study measured how many adult corals survived along the length of the world’s largest reef system following extreme heat stress, and how many new corals they produced to replenish the Great Barrier Reef in 2018. The loss of adults resulted in a crash in coral replenishment compared to levels measured in previous years before mass coral bleaching.
“The number of coral larvae that are produced each year, and where they travel to before settling on a reef, are vital components of the resilience of the Great Barrier Reef. Our study shows that reef resilience is now severely compromised by global warming,” said co-author Professor Andrew Baird.
“The biggest decline in replenishment, a 93% drop compared to previous years, occurred in the dominant branching and table coral, Acropora. As adults these corals provide most of the three-dimensional coral habitat that support thousands of other species,” he said.
“The mix of baby coral species has shifted, and that in turn will affect the future mix of adults, as a slower than normal recovery unfolds over the next decade or longer.”
“The decline in coral recruitment matches the extent of mortality of the adult brood stock in different parts of the Reef,” added Professor Hughes. “Areas that lost the most corals had the greatest declines in replenishment.”
“We expect coral recruitment will gradually recover over the next five to ten years, as surviving corals grow and more of them reach sexual maturity, assuming of course that we don’t see another mass bleaching event in the coming decade,” he said.
So far, the Great Barrier Reef has experienced four mass bleaching events due to global warming, in 1998, 2002, and back-to-back in 2016 and 2017. Scientists predict that the gap between pairs of coral bleaching events will continue to shrink as global warming intensifies.
“It’s highly unlikely that we could escape a fifth or sixth event in the coming decade,” said co-author Professor Morgan Pratchett.
“We used to think that the Great Barrier Reef was too big to fail – until now,” he said.
“For example, when one part was damaged by a cyclone, the surrounding reefs provided the larvae for recovery. But now, the scale of severe damage from heat extremes in 2016 and 2017 was nearly 1500km—vastly larger than a cyclone track.”
Professor Pratchett added that the southern reefs that escaped the bleaching are still in very good condition, but they are too far away to replenish reefs further north.
“There’s only one way to fix this problem,” says Hughes, “and that’s to tackle the root cause of global heating by reducing net greenhouse gas emissions to zero as quickly as possible.”
Hughes T, Kerry J, Baird A, Connolly S, Chase T, Dietzel A, Hill T, Hoey A, Hoogenboom M, Jacobson M, Kerswell A, Madin J, Mieog A, Paley A, Pratchett M, Torda G, & Woods R (2019). ‘Global warming impairs stock–recruitment dynamics of corals’. Nature: http://dx.doi.org/10.1038/s41586-019-1081-y
PHOTOS & VIDEO
A selection of photos and videos relating to the study is available here. Please note that any use of this imagery MUST carry the credit given. In addition, permission must be obtained from the ARC Centre of Excellence for Coral Reef Studies for any use beyond this story.
The Australian Academy of Science have produced a video based on the study. The files are available to embed in online stories at the Dropbox hyperlink above, and the YouTube embed link is here.
CONTACTS FOR INTERVIEWS
Prof Terry Hughes (Pacific Coast Time Zone, USA) Director, ARC Centre of Excellence for Coral Reef Studies Phone: +61 (0)400 720 164 Email: firstname.lastname@example.org
Prof Andrew Baird (Eastern Australia Time Zone) ARC Centre of Excellence for Coral Reef Studies Phone: +61 (0)7 4781 4857 Mobile: +61 (0)400 289 770 Email: email@example.com
Prof Morgan Pratchett (Eastern Australia Time Zone) ARC Centre of Excellence for Coral Reef Studies Phone: + 61 (0)7 4781 5747 Mobile: +61 (0)488 112 295 Email: firstname.lastname@example.org
FOR FURTHER INFORMATION
Melissa Lyne (Eastern Australia Time Zone) Media Manager, ARC Centre of Excellence for Coral Reef Studies Phone: +61 (0) 415 514 328 Email: email@example.com
Recruitment tiles made from terracotta were deployed at 15 reefs along the Great Barrier Reef to quantify coral recruitment after the devastating back-to-back mass bleaching event in 2016–2017. Credit: ARC CoE for Coral Reef Studies/ Gergely Torda