Leslie Massey
Coral reefs are among the most important ecosystems in the world, supporting a quarter of all marine species and providing food and livelihoods for millions of people. However, climate change poses a significant threat to coral reefs in Australia and around the world. The combination of rising ocean temperatures, ocean acidification, and other human activities such as pollution and destructive fishing practices, has led to mass coral bleaching and death events, with Australia's iconic Great Barrier Reef experiencing six such events since 1998. Scientists predict that urgent action is needed to reduce greenhouse gas emissions and protect coral reefs, or we risk losing over 90% of these vital ecosystems by 2050.
| Characteristics | Values |
|---|---|
| Cause of coral reef destruction | Climate change |
| Coral reefs affected | The Great Barrier Reef, the Maldives, Okinawa, North-West Australia, Palau, the Caribbean, the Gulf of Mexico, the eastern Pacific |
| Ocean temperature | Rising |
| Carbon dioxide levels | Rising |
| Ocean acidification | Rising |
| Ocean pH levels | Decreasing |
| Coral calcification rates | Decreasing |
| Coral bleaching | Increasing |
| Coral mortality | Increasing |
| Coral recovery | Slowing |
| Coral breeding | Being explored by scientists |
| Coral reef value to Australia's economy | A$5.6 billion (US$3.84 billion) |
| Global coral reef value | Tens to hundreds of billions of dollars annually |
| Global coral reef loss | 50% |
| Projected coral reef loss by 2050 | 90% |
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What You'll Learn
Ocean warming and coral bleaching
Coral reefs are extremely important ecosystems, supporting a quarter of all known marine species and protecting coastlines during storms. They also contribute to local economies through fisheries and tourism. However, climate change poses an existential threat to the world's coral reefs. The Intergovernmental Panel on Climate Change reports that the oceans have absorbed 90% of the excess heat generated by human-caused global warming. This warming of the oceans is causing coral bleaching, which is a significant issue for Australia's coral reefs.
Coral bleaching occurs when corals are stressed by changes in their environment, including ocean waters that are too warm. When this happens, corals turn white or "bleach". While sometimes the coral is able to recover, other times it dies. Corals are very sensitive to temperature changes, and a rise of just one degree Celsius for four weeks can trigger bleaching. If temperatures stay high for eight weeks or more, the coral will not recover and will begin to die. This process is made worse the higher and longer the temperature stays elevated.
The burning of fossil fuels has been the main driver of ocean warming since the 1970s. The total heat stored by the oceans rose by 187 zettajoules from 1992 to 2019, and most corals cannot survive in these warmer waters. The Great Barrier Reef, the largest reef system in the world, has been severely affected by coral bleaching. In 2024, it suffered the most severe and widespread mass bleaching event ever recorded, with extreme bleaching affecting all regions of the reef. Since 2016, the Great Barrier Reef has suffered five mass bleaching events. Other reefs in Australia, such as those in northwest Australia, including inshore Kimberley, Christmas Island, and Scott Reef, have also experienced severe bleaching.
Scientists are exploring various options to help reefs adapt to climate change and prevent coral bleaching. These include cooling and shading techniques, such as pumping cooler water from the ocean depths to flow over parts of the reef on hot days, and using human-made shade structures. Researchers are also working on landscaping and pest management strategies, such as engineering supports that encourage coral larvae to settle and grow into new reefs. Additionally, biologists are using high-tech coral-breeding techniques to learn how to restore threatened reefs and preserve them as the planet continues to warm.
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Ocean acidification and coral growth
The oceans have absorbed an estimated 20–30% of human-induced carbon emissions, causing their pH levels to plummet. This process is known as ocean acidification. It is a significant threat to coral reefs, as it impedes the ability of corals to build calcium carbonate deposits, which form large reef structures.
Corals are highly sensitive to changes in seawater pH and carbonate chemistry. As the oceans become more acidic, the calcification rates of corals decline. Calcification measurements from coral cores from 328 colonies of the massive coral Porites growing on the Great Barrier Reef in Australia, for example, revealed a 14.2% decline in calcification since 1990.
Ocean acidification has also caused a 13% decline in the skeletal density of massive Porites corals on the Great Barrier Reef since 1950. This thinning of coral skeletons makes them more vulnerable to the compounding effects of climate change, such as ocean warming.
The increase in carbon dioxide in the atmosphere, primarily from the burning of fossil fuels and deforestation, is the main driver of ocean acidification. As the ocean absorbs more carbon dioxide, its chemistry changes, and its pH decreases. This altered seawater chemistry directly impacts the carbonate chemistry of the calcifying fluid used by corals to build their skeletons, resulting in reduced skeletal density and growth.
The effects of ocean acidification on coral growth are complex and vary depending on the coral species and local environmental conditions. However, the overall impact is a significant threat to coral reefs in Australia and worldwide.
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Storms and coral destruction
Climate change is causing an increase in the frequency and intensity of tropical storms, which is one of the main factors contributing to the destruction of coral reefs in Australia. The Great Barrier Reef, a 2,300km-long living organism off Australia's northeastern coast, is considered one of the most species-rich habitats on Earth. However, it has suffered significant coral mortality due to the combined impacts of marine heatwaves, cyclones, and flooding.
The increasing frequency of marine heatwaves leaves corals with insufficient time to recover between stressful events. When corals are exposed to warm ocean waters, they experience thermal stress, which causes them to bleach and eventually die if the high temperatures persist. This process turns the once-vibrant corals into a sickly white shade, robbing the reef of its beauty and threatening the habitat of thousands of marine species that depend on it for survival.
The impact of storms on coral reefs is twofold. Firstly, storms can directly damage coral reefs through physical destruction. The increased intensity of tropical storms poses a significant threat to the structural integrity of coral reefs, which are already weakened by ocean acidification and warming ocean temperatures. Secondly, storms can indirectly contribute to coral destruction by disrupting the ecosystems that protect coral reefs. Mangrove forests, for example, play a crucial role in filtering sediment and protecting coral reefs from the full force of storms and rising sea levels. However, climate change and El Niño have led to the worst mangrove destruction in Australia, removing this vital layer of protection for coral reefs.
The combination of more frequent and intense storms, rising sea levels, and the loss of protective ecosystems creates a perfect storm of threats to Australia's coral reefs. These compounding factors leave the reefs more vulnerable to destruction, even as the increasing frequency of storms continues to batter and erode their structures. The resilience of coral reefs is being pushed to its limits, and without urgent action to address the root causes of climate change, the future of these vital ecosystems hangs in the balance.
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Human activities and pollution
The increase in atmospheric carbon dioxide, a product of human activity, has resulted in warming ocean temperatures. This warming has caused thermal stress in corals, leading to mass coral bleaching events. Coral bleaching occurs when stressed corals expel the microscopic algae that live inside their tissues, revealing their white skeletons. While bleached corals are not dead, they are more susceptible to starvation and disease, and if the algae do not return, the corals will eventually perish.
Additionally, the ocean absorbs a significant amount of human-made carbon dioxide, causing ocean acidification. This process reduces the pH level of the seawater and impairs the ability of corals to build their skeletons and form reefs. The increased acidity makes it difficult for corals to produce the calcium carbonate deposits necessary for large reef structures. As a result, reefs can become vulnerable to shattering during storms and other extreme weather events.
Pollution from land-based sources, including toxicants, sediments, fertilisers, and other chemicals, has also contributed to the degradation of coral reefs. These pollutants can smother corals, reducing their access to light and oxygen, and can also lead to algal blooms, which create murky water conditions that further impede light penetration. The influx of nutrients from these pollutants can also cause imbalances in the reef ecosystem, favouring certain species over others and disrupting the natural balance.
The combination of climate change and pollution has resulted in a significant decline in coral reef health. Scientists predict that if urgent action is not taken to reduce greenhouse gas emissions and pollution, we could lose over 90% of our coral reefs by 2050. This loss would not only impact the diverse marine life that depends on these reefs but also the livelihoods of millions of people who rely on them for food, coastal protection, and economic activities such as tourism and fisheries.
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Strategies for coral preservation
Climate change poses a significant threat to coral reefs in Australia, with rising ocean temperatures, ocean acidification, and other human activities such as pollution and physical damage contributing to the decline of these ecosystems. To address these challenges, scientists and researchers in Australia are developing and implementing various strategies for coral preservation. Here are some key approaches:
Cooling and Shading
One strategy to protect coral reefs from the impacts of rising temperatures is to cool and shade the reefs. This can be achieved by pumping water from cooler depths to flow over the reefs during hot days. Additionally, large, human-made shade structures can be placed over parts of the reefs to provide protection from direct sunlight.
Landscaping and Pest Management
Researchers are also focusing on landscaping and pest management techniques. By engineering supports and structures, researchers aim to encourage coral larvae to settle and grow into new reefs. This involves techniques such as coral gardening, substrate stabilization, coral repositioning, and macro-algae removal.
Coral Breeding and Genetic Modification
Scientists are exploring the potential of breeding and genetically modifying corals to enhance their resilience and adaptability. By utilizing high-tech coral-breeding techniques, biologists aim to restore and preserve coral reefs even as the planet continues to warm.
Reducing Local and Regional Stressors
Historically, management of coral reefs in Australia has focused on mitigating local and regional stressors. This includes addressing issues such as overfishing, oil and gas exploration, coastal development, and poor water quality. By reducing these stressors, the overall health and resilience of coral reefs can be improved.
Coral Reef Restoration and Adaptation
Australia has been witnessing a shift from research and development to implementation in coral reef restoration and adaptation. This includes the integration of intervention and restoration actions into management frameworks, such as the Reef Restoration and Adaptation Program (RRAP), which is one of the world's largest research and development programs focused on coral reefs. This program takes a holistic approach, involving partnerships with Traditional Owners, engineers, social scientists, economists, and other experts to develop coordinated solutions.
Australian Coral Reef Resilience Initiative (ACRRI)
The ACRRI is a AUD27 million, seven-year research program partnership between the Australian Institute of Marine Science and BHP. This initiative takes a 'whole-of-system' approach, combining research in coral re-seeding with healthy reef sounds to attract fish and enhance coral reef resilience. By studying coral seeding, spawning, and coral aquaculture, scientists aim to empower communities to manage and restore their coral reefs effectively.
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Frequently asked questions
Climate change poses a major threat to coral reefs in Australia and around the world. The warming of oceans, caused by increased carbon dioxide and other greenhouse gases, leads to coral bleaching, where corals expel the algae that live inside their tissues, revealing their white skeletons. This makes them more susceptible to starvation and disease. Warmer waters also force marine species to move to cooler habitats, disrupting the ecosystem.
Corals are sensitive to changes in ocean temperature. When stressed by warmer waters, they expel the algae (zooxanthellae) that live inside them and provide them with colour and nutrition. Without the algae, the white skeletons of the corals are exposed, leading to a bleached appearance. While bleached corals are not dead, they are weaker and more vulnerable to starvation and disease.
Coral bleaching can lead to the death of corals if they are unable to recover. Mass coral bleaching events have already caused significant damage to the Great Barrier Reef, with up to 91% of reefs affected in some years. The loss of corals also impacts the thousands of marine species that depend on the reefs for habitat and food, as well as the livelihoods of people who rely on fisheries and tourism associated with healthy reefs.
