Coral reefs are among the most diverse and valuable ecosystems on the planet, supporting marine life, protecting coastlines, and providing a livelihood for millions of people. But these underwater cities are under serious threat from climate change, pollution, and destructive fishing.
In response, scientists and conservationists are actively rebuilding reefs to bring them back to life. But can restoration truly revive these ecosystems to their former glory? A recent study set out to answer this, tracking how corals grow over time and whether restored reefs can reclaim the structure and ecological role of their wild counterparts.
WHY ARE CORAL REEFS IMPORTANT?
Coral reefs play a vital role in supporting marine life. They provide food and shelter for a vast array of species, making them some of the most biodiverse ecosystems on the planet. However, the human benefit of coral reefs are often left untold when we marvel over these beautiful seascapes.
Communities living in close proximity to coral reefs depend on them in a number of ways. The obvious benefit of healthy reefs is food and income for locals1. But coral reefs offer more than just economic benefits, they also serve as natural protectors. Positioned just below the water’s surface, reefs absorb the force of powerful waves and reduces the impact they have on land. This helps shield coastal areas from tropical cyclones and stormy weather. Protection in this form is especially crucial in regions like Southeast Asia, where 71% of the population lives within 10 meters of sea level, making them highly vulnerable to flooding.
However, despite their importance, coral reefs are under serious threat. Rising sea temperatures are causing mass coral bleaching, where corals lose their colour and struggle to survive, while harmful human activities, like blast fishing, further devastate reef habitats. Given these challenges, scientists are working to restore degraded reefs, but how well do restored reefs function compared to natural ones?
REEF RESEARCH
To answer this question, a UK-led research team conducted a field study in Indonesia, working alongside local scientists. They surveyed 18 coral reef sites, categorising them as naturally healthy, degraded, or restored. The healthy and damaged reefs were used as control sites, which creates a sort of measuring stick to compare the restored reefs to and see how they perform in comparision to naturally healthy and degraded reefs.
In the restored sites, corals were carefully transplanted onto hexagonal frames, creating a foundation for growth (see image below). To track progress, researchers measured coral size, coverage, and frequency at the start of the experiment and then revisited the site four years later. Using advanced software, the team transformed this data into information on coral growth and density, which in turn allowed them to calculate the reef’s carbonate budget.
WHAT IS A CARBONATE BUDGET?
The carbonate budget is essentially a measure of how much calcium carbonate (a material corals use to build their skeletons) is being added to the reef compared to how much is being lost. Corals grow through a process called accretion, where they build layers of calcium carbonate on their skeleton, creating the physical structure of the reef. At the same time, natural processes like erosion, coral-eating fish, and damage from storms wear this structure away. A positive carbonate budget means the reef is growing faster than it’s eroding, which is essential for the reef to thrive and keep up with rising sea levels. Conversely, a negative budget indicates that the reef is shrinking, putting marine habitats at risk.
WHAT DOES THE RESEARCH TELL US?
Four years after the project began, the results were striking. The restored reef’s carbonate budget had tripled and the accretion (growth) rate was 30% higher than the naturally healthy reefs. The researchers even described the restoration sites as ‘indistinguishable’ from the naturally healthy reefs.
But there was a catch…although the reefs were making miraculous recoveries, they were dominated by fast-growing corals and lacking the complexity of naturally healthy reefs. This is important as coral diversity is essential for supporting a wide variety of marine species.
A healthy reef is like a bustling city, with different corals creating habitats for different types of fish and other marine life. If restoration efforts only succeed in bringing back one or two types of fast-growing coral, the reef may not be able to support the same level of biodiversity as a naturally healthy reef2. This lack of full natural functionality in the reef was further confirmed by the study as they found that parrotfish, a key species to the function of coral reef ecosystems, were low in numbers at the restoration sites.
The results of this study, therefore, show how important it is to not only focus on the quantity of coral recovery but also in the quality. Just like we need variety in our diet to keep us healthy, reefs need diversity in their corals to support the marine animals that rely upon them.
HOW TO FIND ANOTHER WAY?
Sadly, this study is more about the effectiveness of current conservation efforts and where further research is needed to help these reefs recover to their former glory.
However, if we were to address the cause of the issue, which is rising sea temperatures and the bleaching of corals, we can see where our efforts need to lie. Obviously, global warming and carbon emissions are a international issue that needs to be addressed by government leaders, but we can always do our little bit by looking at our own carbon footprints. A really cool tool to see how much carbon you emit where you use the most carbon is the Carbon Calculator by WWF.
Additionally, if you do get the opportunity to visit these amazing underwater gardens, practicing responsible tourism, such as avoiding touching or disturbing corals and using reef-safe suncream are really good ways to protect them.
Article written by Sarah Bellis
Primary paper:
Lange, I.D. et al. (2024) ‘Coral restoration can drive rapid reef carbonate budget recovery’, Current Biology, 34(6). doi:10.1016/j.cub.2024.02.009.
Other references:
Cinner, J.E. et al. (2012) ‘Vulnerability of coastal communities to key impacts of climate change on Coral Reef Fisheries’, Global Environmental Change, 22(1), pp. 12–20. doi:10.1016/j.gloenvcha.2011.09.018.
Pratchett, M.S. et al. (2011) ‘Changes in biodiversity and functioning of reef fish assemblages following coral bleaching and coral loss’, Diversity, 3(3), pp. 424–452. doi:10.3390/d3030424.
