Degraded coral reefs can rebuild with “incredible” speed, but it may be little comfort to those concerned about the immediate impact of climate change on places like the Great Barrier Reef (GBR).
Overnight authorities confirmed another mass bleaching event is underway on the GBR.
But some good news comes from a 4-year research project undertaken on 3 reefs off Indonesia’s coastline that were destroyed by blast fishing in the 1980s and 90s.
Scientists used a sand-coated steel frame on top of the rubble at the study sites and transplanted new coral.
They then monitored the rate carbonate was produced by the coral transplants. Tiny coral polyps secrete calcium carbonate which can house other polyps, eventually forming large stony skeletons and forming big reefs.
Monitoring the increase of the calcium carbonate as it is secreted by polyps and eroded by other organisms living on the reef enabled the research team to understand whether transplantation was successful.
Within 4 years, net carbonate levels had tripled and the transplants grew at rates similar to existing healthy sites.
“The speed of recovery that we saw was incredible,” says the lead researcher, Dr Ines Lange, from the University of Exeter in the UK. “We did not expect a full recovery of reef framework production after only 4 years.”
But she cautions this growth project only applies to severely degraded coral reefs and is unlikely to solve the major threats posed by climate change and ocean acidification.
That view is echoed by Australian marine biologists as the fifth mass coral bleaching event of the Great Barrier Reef in the past 8 years has been declared.
Another GBR mass bleaching event underway
The Great Barrier Reef Marine Park Authority confirmed on Friday the mass bleaching event was underway, saying “most surveyed reefs and results are consistent with patterns of heat stress that has built up over summer”.
Many northern hemisphere coral reefs have suffered bleaching as a result of the El Nino climate event in 2023, and the current bleaching in the GBR may signify a global-scale event is underway.
Coral bleaching occurs when the relationship between corals and algae breaks down due to stress. Healthy stone corals house zooxanthellae – tiny single-celled algae – embedded in their structure, providing shelter and chemicals needed for them to photosynthesise.
In turn, the algae supply the glucose sugar produced during photosynthesis to the coral, used for energy to perform its own functions and continue growing its calcium carbonate skeleton.
When changes in light, temperature or ocean acidity are felt by the coral, it ejects the algae, leading to the loss of coral colour and the ‘bleaching’.
These events are deeply concerning to marine scientists. This process likely began more than 210 million years ago and is essential for preventing coral death.
Director of the Australian Research Council Centre of Excellence for Coral Reef Studies, Professor Terry Hughes, says any promise of reef restoration through transplantation is being rapidly scotched by larger climate events like bleaching.
“It’s delusional to think that coral restoration is a solution to the global destruction of reefs by anthropogenic climate change,” Hughes says. “Worse, it detracts attention away from the urgent imperative to reduce greenhouse gas emissions.”
“The scale of this study is tiny compared to the amount of corals dying every hot summer, as temperatures continue to rise globally.
“For example, you would need to raise and out-plant roughly 250 million adult corals, each the size of a large dinner plate, to increase coral cover on the Great Barrier Reef by 1%. And the Great Barrier Reef right now is experiencing severe coral bleaching for the 5th time in 8 summers.”
His views are echoed by Dr Jen Matthews, deputy team leader for the University of Technology Sydney’s Future Reefs Program.
Matthews believes the specific line of the Indonesian reef study does hold some hope for regrowing reefs that have been physically destroyed in the past.
“There is no doubt that immediate action to address climate change is vital to safeguard the future of coral reefs,” she says.
“But restoration practices like coral transplantation can help buy time for reefs and expedite recovery once comprehensive measures are in place to combat climate change.
“The researchers [of the Indonesia study] acknowledge that this practice tends to focus on a limited number of fast-growing species driving the gains in carbonate production, coral cover, and structural complexity, but lack the immense diversity typically found in a fully functional reef.
“This helps to justify the current coral transplantation efforts conducted across Australia, but also the need for more restoration practices that build genetic diversity, and not just coral cover.”
