A coral 'rope' nursery in the MaldivesLuca Saponari/University of Milan, CC BY-ND
Coral reefs are much more than just a pretty place to visit. They are among the world’s richest ecosystems, hosting about a third of all marine species.
These reefs also directly benefit more than a billion people, providing livelihoods and food security, as well as protection from storms and coastal erosion.
Without coral reefs, the world would be a much poorer place. So when corals die or become damaged, many people try to restore them. But the enormity of the task is growing as the climate keeps warming.
In our new research, we examined the full extent of existing coral restoration projects worldwide. We looked at what drives their success or failure, and how much it would actually cost to restore what’s already been lost. Restoring the reefs we’ve already lost around the world could cost up to A$26 trillion.
Bleached Acropora corals in the Maldives.Davide Seveso/University of Milan
When sea temperatures climb above the seasonal average for sustained periods, corals can become bleached. They lose colour as they expel their symbiotic algae when stressed, revealing the white skeleton underneath. Severe bleaching can kill coral.
Over the past 40 years, the extent of coral reefs has halved. As climate change continues, bleaching events and coral deaths will become more common. More than 90% of coral reefs are at risk of long-term degradation by the end of the century.
Dead corals in the Maldives following a bleaching event.Simone Montano/University of Milan
But by far the most common type of restoration is “coral gardening”, where coral fragments grown in nurseries are transplanted back to the reef.
The problem is scale. Coral restoration can only be done successfully at a small scale. Most projects only operate over several hundred or a few thousand square metres. Compare that with nearly 12,000 square km of loss and degradation between 2009 and 2018. Restoration projects come nowhere near the scale needed to offset losses from climate change and other threats.
Conservationists work to garden coral and help preserve these unique life forms.
Sky-high costs
Coral restoration is expensive, ranging from around $10,000 to $226 million per hectare. The wide range reflects the variable costs of different techniques used, ease of access, and cost of labour. For example, coral gardening (coral fragments grown in nurseries transplanted back to the reef) is relatively cheap (median cost $558,000 per hectare) compared with seeding coral larvae (median $830,000 per hectare). Building artificial reefs can cost up to $226 million per hectare.
We estimated it would cost more than $1.6 billion to restore just 10% of degraded coral areas globally. This is using the lowest cost per hectare and assuming all restoration projects are successful.
Even our conservative estimate is four times more than the total investment in coral restoration over the past decade ($410 million).
But it’s reasonable to use the highest cost per hectare, given high failure rates, the need to use several techniques at the same site, and the great expense of working on remote reefs. Restoring 10% of degraded coral areas globally, at $226 million a hectare, would cost more than $26 trillion – almost ten times Australia’s annual GDP.
It is therefore financially impossible to tackle the ongoing loss of coral reefs with restoration, even if local projects can still provide some benefits.
Rope nurseries nurture coral fragments until they’re ready to be planted out.Luca Saponari/University of Milan
Location, location, location
Our research also looked at what drives the choice of restoration sites. We found it depends mostly on how close a reef is to human settlements.
By itself, this isn’t necessarily a bad thing. But we also found restoration actions were more likely to occur in reefs already degraded by human activity and with fewer coral species.
This means we’re not necessarily targeting sites where restoration is most likely to succeed, or of greatest ecological importance.
Another limitation is coral gardening normally involves only a few coral species – the easiest to rear and transplant. While this can still increase coral cover, it does not restore coral diversity to the extent necessary for healthy, resilient ecosystems.
Measuring ‘success’
Another sad reality is that more than a third of all coral restoration efforts fail. The reasons why can include poor planning, unproven technologies, insufficient monitoring, and subsequent heatwaves.
Unfortunately, there’s no standard way to collect data or report on restoration projects. This makes it difficult – or impossible – to identify conditions leading to success, and reduces the pace of improvement.
Succeed now, fail later
Most coral transplants are monitored for less than 18 months. Even if they survive that period, there’s no guarantee they will last longer. The long-term success rate is unknown.
When we examined the likelihood of extreme heat events immediately following restoration and in coming decades, we found most restored sites had already experienced severe bleaching shortly after restoration. It will be difficult to find locations that will be spared from future global warming.
Sometimes the young coral is bleached before the restoration project is complete.Davide Seveso/University of Milan
No substitute for climate action
Coral restoration has the potential to be a valuable tool in certain circumstances: when it promotes community engagement and addresses local needs. But it is not yet – and might never be – feasible to scale up sufficiently to have meaningful long-term positive effects on coral reef ecosystems.
Other conservation approaches such as establishing, maintaining and enforcing marine protected areas, and improving water quality, could improve the chance a coral restoration project will work. These efforts could also support local human communities with incentives for conservation.
Reinforcing complementary strategies could therefore bolster ecosystem resilience, extending the reach and success of coral restoration projects.
Corey J. A. Bradshaw receives funding from the Australian Research Council.
Clelia Mulà receives funding from the Australian Institute of Marine Science.
Giovanni Strona does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Australia has huge reserves of coal and gas – but very little oil. Before the 20th century, this didn’t matter – trains ran on local coal. But as cars and trucks have come to dominate, Australia has become more and more reliant on imported oil.
Imports now account for around 80% of total refined fuel consumption, the highest level on record.
If the flow of oil stopped due to war or economic instability, Australia would have about 54 days worth in storage before we ran out. That would be a huge problem.
But as more drivers switch from petrol and diesel to electric cars, this equation will change. We can already see this in China, where a rapid uptake of electric vehicles has seen oil demand begin to fall.
On one level, ending Australia’s dependence on foreign oil makes sense at a time of great geopolitical uncertainty. But on the other, going electric would lead to more reliance on China, now the world’s largest manufacturer of EVs.
Reducing reliance on oil makes clear sense for climate and national security reasons. But going electric has to be done carefully, to ensure Australia isn’t reliant on just one country.
The last two refineries rely on imported crude oil, as Australian oil from the North-West Shelf largely isn’t suitable for local refining.
As a result, Australia is more reliant than ever on importing fuels from large refineries in Asia such as South Korea, Singapore and Malaysia. In 2023, around 45,000 megalitres of fuel were imported from these nations.
Almost three-quarters (74%) of these liquid fuels are used in transport, across road, rail, shipping and air transport. But road transport is the big one – our cars, trucks and other road vehicles use more than half (54%) of all liquid fuels.
In January, Australia had 30 days worth of petrol. Our stores of all types of oil are a bit higher, at 54 days worth. But that’s still well short of the 90 days the International Energy Agency (IEA) requires of member nations.
Electricity made locally
Shifting to electric vehicles promises cleaner air and far lower ongoing costs for drivers, as electricity is much cheaper than petrol or diesel and maintenance is far less.
But there’s another factor – the energy source. Australia’s electricity is all produced and consumed inside its borders, using local resources (sun, wind, water, coal and gas).
In this respect, electric vehicles offer much greater energy security. A war in the Middle East or a trade war over tariffs would not bring Australia to a halt. This is one reason why China has so aggressively gone electric – to end its soaring dependence on foreign oil.
Mainstreaming EVs in Australia will mean accelerating production of renewable electricity further so we can power not just homes and industry but charge cars, trucks and buses, too.
Doing this would boost our energy security, break our dependency on imported oil and drive down emissions.
Ending our dependence on oil will be slow. Australia Institute research estimates 8% of imported fuels could be replaced by local electricity once EVs make up 25% of the passenger car fleet. At 100% EVs, we would reduce oil demand by 33%.
The other two-thirds of demand is largely from trucks, planes and ships. Electric trucks are coming, but the sector isn’t as mature as electric cars. It’s a similar story for planes and cargo ships.
All electricity in Australia is produced locally. For transport, that’s a boon to energy security.Marian Weyo
Energy security and EVs
Australia doesn’t manufacture EVs at scale. As a result, we import EVs from the top manufacturing nations. China is far and away the leader, building 80% of Australia’s new EVs.
Australia is a major producer of critical minerals essential to the manufacture of EVs, as well as other green technologies such as lithium, cobalt and nickel. But China dominates much of the global supply chain for refining these minerals and manufacturing batteries.
There’s a risk in relying largely on one country for EVs, especially given the present geopolitical instability.
EVs unquestionably offer large benefits for Australia’s energy security by steadily reducing our reliance on imports from volatile global oil markets.
But this has to be balanced with other security concerns, such as a heightened reliance on China, as well as the privacy and security risks linked to data collection from digitally connected EVs.
A balanced approach would see authorities emphasise energy independence through renewables and strong support for vehicle electrification through legislative and regulatory frameworks.
This approach would reduce new security risks while unlocking the environmental and economic benefits of widespread EV adoption.
Hussein Dia receives funding from the Australian Research Council, the iMOVE Australia Cooperative Research Centre, Transport for New South Wales, Queensland Department of Transport and Main Roads, Victorian Department of Transport and Planning, and Department of Infrastructure, Transport, Regional Development, Communications and the Arts.
If left unaddressed, many environmental changes in Aotearoa New Zealand could threaten livelihoods, health, quality of life and infrastructure for generations to come, according to the latest update on the state of the environment.
The Ministry for the Environment and StatsNZ produce an environmental assessment every three years, collating data and trends on air quality, freshwater and marine environments, the land and climate.
The latest report shows that long-term drivers of change – including international influences, economic demands and climate change – mean many natural systems have become less resilient and are at risk of collapse. But it also highlights improvements in urban air quality and reduced waste flows to landfill.
Real risks to people, communities and places
Many environmental trends in New Zealand are sobering.
Soil erosion is increasing and continues to degrade downstream freshwater and marine ecosystems. Soils misplaced from land, including through landslides or gradual loss of topsoil, can threaten homes and infrastructure and reduce the potential for growing food or storing carbon.
Climate change is projected to increase erosion rates by up to 233%, depending on future emissions scenarios.
Native forests are most effective at reducing soil erosion, but exotic forests can also help. The report shows the area planted in exotic forest has increased by 12% (220,922 hectares) between 1996 and 2018, with most of this new area coming from exotic grassland.
Landfill contaminants, including leachates and microplastics, threaten soil health. New Zealand remains the highest producer of waste to landfill per capita among developed countries, but waste flows to landfill have dropped by 11% in 2023, compared with a 2018 peak.
The report offers another glimmer of progress. While air pollution still affects health, long-term air quality is gradually improving thanks to a shift away from cars with combustion engines.
Population growth and urban development are displacing green spaces.Getty Images
Water quality and green spaces
What happens on land commonly flows into water, often affecting human health and recreation. The report shows that between 2019 and 2024, nearly half of all groundwater monitoring sites failed to meet drinking water standards for E. coli at least once. Nitrate concentrations also rose at around half of all sites.
Freshwater ecosystems are critically affected by the space we give them. Urban development can displace natural features such as wetlands and floodplains, which store water and provide a buffer against extreme weather events.
Four in five New Zealanders live in urban areas and the report shows green spaces have not kept up with population growth. Continued development near rivers and on floodplains, without maintaining natural buffers, increases risks to homes and infrastructure as flood extremes worsen with climate change.
Coastal areas face their own challenges. Rising seas and storm surges threaten not only homes and roads, but also culturally significant places. As many as 420 archaeological sites on public conservation land are at risk of coastal inundation and 191 marae are within one kilometre of the coast.
Livelihoods and biodiversity at risk
New Zealand is a globally significant biodiversity hotspot and natural landscapes are central to cultural identity. The land and waters, and species we share them with, are inseparable from M?ori identity. The economy, from agriculture to tourism, also depends on thriving ecosystems.
But many pressures on biodiversity are worsening, according to the report. About 94% of native reptiles and 78% of native birds are threatened or at risk of extinction.
Extreme weather events (expected to increase with climate change) threaten food and fibre crops. The report estimates the recovery of these sectors from Cyclone Gabrielle will cost up to NZ$1.1 billion.
Pest species continue to damage ecosystems at a cost of $9.2 billion in 2019–20, including primary-sector losses of $4.3 billion.
Wilding conifers are a particular concern, having invaded an estimated two million hectares of land, primarily on the conservation estate. Without careful management, the report projects they could cover up to 25% of New Zealand’s land within 30 years.
The restoration of Te Auaunga, Auckland’s longest urban river, is helping to reduce flooding and improve recreational spaces.Shutterstock/aiyoshi597
Stories behind the numbers
For the first time, the ministry has released a companion report to share stories of hope.
It highlights the links between environmental challenges and how nature-based approaches can benefit both people and the environment.
In Tair?whiti, for instance, a native forest restoration project is protecting Gisborne’s drinking water supply. A large block of commercial pine is being replaced with native forests to stabilise erodible land, filter water runoff before it reaches dams, and provide habitat for native flora and fauna.
In Auckland, the Making Space for Water program is restoring Te Auaunga (Oakley Creek), the city’s longest urban river. The work includes widening the river channel, removing restrictive structures and planting native vegetation to regenerate historical wetland habitats. Along with reducing flooding in the area, these changes provide improved recreational spaces for people.
The report notes the complexity of interactions between people and the natural environment, which means that many impacts cannot be seen straight away. For instance, nitrates move through groundwater very slowly and we may continue to see the effects of past decisions for some time yet. Furthermore, climate change can amplify many environmental stressors.
The state of our environment mirrors our collective decisions. This update offers an opportunity to guide those decisions towards a more resilient future.
Christina McCabe is affiliated with Te Whare W?nanga o Waitaha / The University of Canterbury, and Te P?naha Matatini, a Centre of Research Excellence.
Queensland’s greenhouse gas emission reduction targets will be reviewed, with the treasurer saying gas will play a “critical role” in supply reliability and reaffirming the government’s commitment to delivering net zero by 2050.
In the mid-2000s, there was little life to be found at Bottle Bend Reserve on the Murray River. Today, the river bend is home to an array of plant and animal life, thanks to a dedicated group of local volunteers.
