Sign In
International; NSW; VIC; QLD
Media release
From:
Good news for coral reef restoration efforts: Study finds “full recovery” of reef growth within four years
While the majority of the world’s reefs are now under threat or even damaged potentially beyond repair, a new study reported in the journal Current Biology on March 8 offers some encouraging news: efforts to restore coral reefs not only increase coral cover, but they can also bring back important ecosystem functions, and surprisingly fast.
“We found that restored coral reefs can grow at the same speed as healthy coral reefs just four years after coral transplantation,” says Ines Lange (@InesLange9) of University of Exeter, UK. “This means that they provide lots of habitat for marine life and efficiently protect the adjacent island from wave energy and erosion.”
“The speed of recovery that we saw was incredible,” she says. “We did not expect a full recovery of reef framework production after only four years.”
The work by Lange and her international colleagues represents the first reef carbonate budget trajectories at any coral restoration sites. The study was conducted at the Mars Coral Reef Restoration Programme in South Sulawesi, Indonesia, one of the largest restoration projects in the world. The project relies on transplanting corals and adding substrate to restore reefs badly damaged by blast fishing 30 or 40 years ago. Without human intervention, those reefs had shown no signs of recovering due to the presence of loose coral rubble that prevents young coral larvae from surviving.
The restoration effort has added a continuous network of sand-coated steel structures to consolidate the rubble and offer a structure for transplanting coral fragments. The question was whether and how quickly such restored sites would recover. To find out, the researchers measured the carbonate budgets of 12 sites that had been restored at different times, up to four years ago.
“Corals constantly add calcium carbonate to the reef framework while some fishes and sea urchins erode it away, so calculating the overall carbonate budget basically tells you if the reef as a whole is growing or shrinking,” Lange says. “Positive reef growth is important to keep up with sea-level rise, protect coastlines from storms and erosion, and provide habitat for reef animals.”
They wanted to know how long it takes to bring back healthy reef growth and its associated functions. Their data show that rapid growth of transplanted corals supports the recovery of coral cover and carbonate production. In fact, just four years in, the net carbonate budget had tripled such that it matched that at healthy control sites.
There were some important differences, however. Because branched corals had been transplanted preferentially over other corals, the makeup of the restored reef communities differs. The researchers say those differences “may affect habitat provision for some marine species and resilience to future heatwaves, as branching corals are more sensitive to bleaching.”
While longer-term study is necessary to see what happens over time and under stress, the findings show that active management actions can help to boost the resilience of reefs and bring back important ecosystem functions that are critical for marine life and local communities in relatively short periods of time, according to the researchers. They’re hopeful that, over time, restored reefs will naturally recruit a more diverse mix of coral species. However, they note that what will happen in any given location around the world will depend on many factors, including environmental conditions and restoration techniques.
“As is so often the case, there is no one-size-fits-all solution, but we hope that this positive example can be used as inspiration for other reef restoration projects around the world,” Lange says.
“These results give us the encouragement that if we can rapidly reduce emissions and stabilize the climate, we have effective tools to help regrow functioning coral reefs,” says Tim Lamont (@TimACLamont), a study co-author at the Lancaster Environment Centre, Lancaster University, UK.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Honorary Associate Professor Robert Day (retired) is from the School of Biosciences at the University of Melbourne
The paper is impressive. Coral reef bleaching and subsequent reef degradation is one of the first tipping points (that is: irreversible changes) we can expect as a result of Climate Change. This study reports on results from one of the largest coral restoration programs.
Corals construct a limestone (Calcium Carbonate) skeleton. Provided the chunks of limestone do not roll around in the wave surges, they become cemented together by species of limestone-producing “coralline algae” (seaweeds), and coral juveniles can establish and grow on the base, so that the reef grows upwards.
Important aspects of this process are the carbonate production rate (how fast the limestone chunks are produced), how much of the reef is covered by living coral, and the vertical reef accretion (how fast the reef grows upwards towards the sea surface).
Another important aspect is “structural complexity” – the variety of holes and other spaces between the coral branches, which offer places for fish and other animals plus various seaweeds to live. This is largely responsible for the huge diversity of species on coral reefs. It partly depends on the types of corals on the reef.
So this study, which claims that restoring coral reefs can bring back coral cover, coral growth rates and ecosystem functions in 4 years, would appear to be extremely important. But the study was not done on reefs damaged by climate change, and the measurements made could not predict ecosystem effects with much confidence, so we cannot be sure these results will apply to attempts to recover reefs damaged by climate change – I have explained this further in section 3, on “Significance and drawbacks of the results”.
My opinion of the quality of the research
The study was done on reefs in Indonesia that were destroyed 30-40 years ago using dynamite – blasting kills fish as well as breaking the corals and was used to harvest and sell fish. Steel frames were laid over the reefs to stop the dead coral chunks moving around; and pieces of living coral were attached to the steel bars. As there were living reefs nearby, there were also many coral larvae in the waters that could attach and grow. Using restoration of extensively damaged reefs like these is a good idea, as so far climate change events have had patchy effects, and these are good methods to use.
The design of the experiment was fairly good. 3 degraded reefs and 3 healthy reefs were used as controls, to compare with 12 reefs that had been restored at various times. But the positions of the variously treated reefs should be well mixed to be fully confident that differences are not due to different conditions in different places. In this case the 3 degraded controls, all the reefs restored from 2 years to a few months ago plus one reef restored 4 years ago were in one area, while the 3 healthy reefs and two 4 year-old restored reefs were in another area about 1km away. It seems very unlikely that the results would be different if the locations had been well-mixed, but it is possible that the healthy reefs might have always been different from the reefs in the first area, biasing the results.
The significance and drawbacks of the results
If we assume that healthy reefs would be similar between the two areas, the results indicate degraded reefs recover in 4 years, in terms of the number of coral colonies in a fixed area, and especially coral cover and how fast the limestone is produced. That is very good news. These last two are mostly due to growth of the transplanted pieces of branching corals.
How fast the reefs grow upwards was estimated based on the production of limestone minus the erosion rate (which was close to zero at all the sites). But how good a measure this is of the actual rate that reefs grow upwards is debatable, particularly as the coral species used in restoration were branching corals which can be easily damaged in storms. Despite the discussion by the authors of this process, I think we have yet to discover whether restored reefs can grow upwards fast enough to keep up with rising sea levels.
The structural complexity of reefs is important for the ecosystem on coral reefs. It was measured by “substrate rugosity”. But I suspect this measure does not accurately predict the degree to which the reefs would provide habitats for other species. The authors note that the branching corals used in restoration do not provide the larger-scale framework that massive corals do. So while rugostiy reaches the level of natural reefs in 4 years, which is good news, I think we do not know if the habitat offered to other species is fully recovered.
Climate change will result in widespread warm water events that will kill corals over large areas, and these warm events may be repeated over time. Further, some of the extra CO2 in the air dissolves in the oceans, making them more acid. This means that these restoration methods may not work, unless corals (or the tiny plants that live in their tissues) can be adapted to survive in warmer and more acid waters, and enough of these adapted types can be produced to plant over large areas to recover reefs. The authors discuss the prospects for reef restoration under climate change, but despite their encouraging results, there are still many hurdles to be overcome before we know whether this will be possible.
What this means for Australians
The study is encouraging, as it shows that coral cover can recover fast if good methods are used to stabilise the damaged reefs so that the rubble can be cemented together by algae that grow on them, forming a firm base for future coral growth, and if healthy branches of fast-growing corals are transplanted and fixed in place. But to survive climate change, these corals must be resistant to warmer and more acid water, unlike those used in this study. There is great work being done by collaborators in a number of Australian Universities on trying to adapt the tiny algae that live inside corals to these conditions, but the scale of the problem is immense. There need to be enough of these resistant corals produced to plant out in very large areas of the great Barrier reef (and elsewhere) once these reefs are badly damaged.
The authors also discuss the implications of the fact that reefs in this area grow fast compared to many other areas; and they have low erosion because parrotfish (which scrape reefs) have been heavily fished. This means that we can expect slower growth on the Great barrier and Ningaloo reefs, as fishing of scraping parrotfish is very limited in Australia. This means that the recovery may be somewhat slower. Our reefs have more fish of other types too, which may mean that the ecosystem around the reefs is more resilient, provided we can recover the corals quickly enough to maintain the habitat structure.
Professor Terry Hughes is Director of the Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies, housed at James Cook University
The paper claims that we can restore tiny patches of coral reefs 'if we can maintain climate conditions that allow for coral survival.' That’s a very big 'if' - as demonstrated last summer in Florida – where coral restoration projects were destroyed by record-breaking sea temperatures.
It’s delusional to think that coral restoration is a solution to the global destruction of reefs by anthropogenic climate change. 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.
Dr Jen Matthews is Deputy Team Leader for the Future Reefs Program from the University of Technology Sydney
There is no doubt that immediate action to address climate change is vital to safeguard the future of coral reefs. But restoration practices like coral transplantation can help to buy time for reefs and expedite recovery once comprehensive measures are in place to combat climate change.
This study provides compelling evidence of how coral transplantation can help to stabilise loose foundations, rebuild degraded reefs, and restore certain ecosystem functions. The researchers 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.
It's crucial to recognise that coral transplantation is just one tool in our restoration toolbox, and it can work in tandem with other methods to promote greater diversity. As the authors highlight, the loose rubble in these degraded sites poses a challenge to the growth of baby corals. Nevertheless, coral transplantation and substrate addition creates a solid foundation that facilitates coral reseeding, which supports the survival of millions of diverse coral babies produced during mass reproduction.
Multimedia
Attachments
Note: Not all attachments are visible to the general public. Research URLs will go live after the embargo ends.
