Helena Joyce
The Great Barrier Reef is the world's largest living reef system, and it is under threat from pollution. Water pollution is considered one of the highest risks to the Great Barrier Reef's health, impacting critical habitats for threatened dugongs, turtles, dolphins, seabirds, fish, and other marine life. The runoff of pollutants from agriculture, tree clearing, overgrazing, coastal development, and other human activities has led to increased sedimentation, higher algal growth, and the buildup of pollutants in the Reef, compromising the health of coral, seagrass, and marine ecosystems. Additionally, plastic pollution, which makes up over 80% of marine debris found on the Reef, poses a significant threat to marine life and can enter the food chain, affecting human health. Climate change, with rising carbon dioxide levels, also exacerbates the problem, increasing water temperatures and the frequency and intensity of rainfall, leading to higher levels of pollutants entering the Reef. To protect the Great Barrier Reef, collective action is required to reduce water pollution, limit plastic waste, and decrease carbon emissions through sustainable choices and behaviour changes.
| Characteristics | Values |
|---|---|
| Type of pollution | Water, plastic, carbon emissions, overfishing |
| Water pollution sources | Urban runoff, agricultural practices, improper waste management, tree clearing, overgrazing, failed septic systems, coastal development, deforestation, oil and chemical spills, road construction |
| Water pollution effects | Reduced light for seagrass and coral growth, coral bleaching, reduced coral diversity, disease and mortality in sensitive species, coral loss, decline in biodiversity |
| Plastic pollution effects | Harm to marine life, turtles, dugongs, dolphins, seabirds, human health |
| Carbon emissions effects | Severely compromised ecosystem, threats to species like seabirds, fish, marine reptiles, plankton |
| Overfishing effects | Depletion of key reef species, damage to coral habitat |
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What You'll Learn
Water pollution from agricultural runoff
Excessive fertiliser applied to crops like sugarcane can wash into rivers and waterways, ultimately reaching the Great Barrier Reef. Nitrogen from these fertilisers is linked to harmful algal blooms, which block sunlight, reducing coral's resilience to bleaching and coral diversity. Increased sedimentation and nutrients can also cause higher algal growth, leading to a build-up of pollutants in sediments and marine species, and smothering corals.
Agricultural pesticides are widely used in Queensland to manage pests and protect crops. When it rains, these chemicals wash off the land and flow into the reef, where they can inhibit photosynthesis in marine plant species such as seagrasses. Pesticides and herbicides have been detected in high concentrations in inshore areas, posing risks to marine plants and animals. Tree clearing and overgrazing cause soils to erode and wash into creeks and rivers that run into the Great Barrier Reef, contributing to the sedimentation issue.
To address these issues, the Queensland government passed a bill in 2019 to improve water quality flowing into the reef from agricultural properties. The regulations target practices that pose the greatest risk to water quality, such as overusing fertiliser. Additionally, efforts are being made to reduce the level of sediment, nutrients, and pesticides entering the reef, through improved land management and rehabilitation initiatives.
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Climate change and increased rainfall
Climate change is the single biggest threat to the Great Barrier Reef. The rise in ocean temperatures is primarily caused by an increase in carbon dioxide and other greenhouse gas emissions. Carbon dioxide levels have been steadily rising for over a century, and the ocean absorbs this carbon dioxide, making it more acidic. This process is known as ocean acidification, and it hinders the ability of corals to build skeletons and form coral reefs.
The Great Barrier Reef, as a coastal region, is particularly vulnerable to severe weather events such as cyclones, flooding, and storms. Between 2004 and 2018, ten cyclones of category three or higher intensity crossed the Great Barrier Reef, causing significant damage to the coral reefs. As water temperatures continue to rise, marine species are forced to migrate southward in search of cooler habitats. This shift results in increased competition for food and shelter, endangering the entire ecosystem.
The impact of climate change on coral spawning patterns further exacerbates the situation. Research suggests that changing sea temperatures influence the timing of coral spawning. While the exact reason is not yet fully understood, one theory suggests that sea temperature may affect sperm's swimming ability, while another theory posits that temperature regulates sperm and egg production. As a result, the month of coral spawning could become "decoupled" from other critical ecosystem processes as climate change progresses.
Moreover, the Great Barrier Reef is facing the challenge of coral bleaching due to heat stress. When corals experience heat stress, they expel the microscopic algae living in their tissues, exposing their white skeletons. Although bleached corals are not dead, they are more susceptible to starvation and disease. Marine heatwaves have already triggered mass coral bleaching events, reducing shallow water coral reefs by up to 50%.
To address these issues, urgent global action is required to drastically reduce greenhouse gas emissions and mitigate the impact of climate change on the Great Barrier Reef. Efforts must also focus on strengthening key ecosystems like seagrass meadows, mangroves, and wetlands, which play a crucial role in absorbing carbon dioxide and combating climate change.
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Plastic pollution and marine debris
A three-year study of plastic waste in the central Great Barrier Reef World Heritage Area concluded that there is a chronic risk to marine life from plastic exposure. Microplastics, plastic particles smaller than five millimetres, are of particular concern as they can be ingested by marine organisms. These microplastics often come from personal care products, synthetic clothing materials, and larger pieces of plastic that break down into smaller fragments. Extreme weather events, such as storms, can increase the outflow of plastic debris from rivers, contributing to the plastic pollution in the ocean.
Plastic debris smothers coral reefs, suffocating and killing corals, sponges, and other invertebrates. It also increases the likelihood of coral diseases. This is evident in some of the most remote and uninhabited reefs, where plastic pollution has been found floating amidst otherwise healthy ecosystems. The impact of plastic pollution is more pronounced in low and middle-income countries, where limited resources for waste management and better fishing gear contribute to higher levels of plastic waste in the ocean.
Fishing gear, or 'ghost gear', is a significant source of plastic pollution on the Great Barrier Reef. This includes nets, traps, pots, lines, and artificial drifting fish aggregating devices. Cyalume glowsticks, used in pelagic and longline fisheries, have also been identified as a primary source of plastic pollution. These glowsticks can disrupt fish behaviour and are toxic to marine life and humans. Additionally, plastic waste from aquaculture farming can enter oceans and rivers, further contributing to the problem.
To address plastic pollution and marine debris, collective action is required from the community, industry, and government. This includes choosing sustainable options, minimising waste, and engaging in stewardship activities. Individuals can reduce their plastic consumption by refusing single-use plastics, reusing and recycling, and opting for reusable alternatives. Governments and industries should also work together to implement policies and practices that minimise waste and promote sustainable behaviours.
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Overfishing and coral depletion
The Great Barrier Reef is a precious ecosystem that is under serious threat from pollution and human activities. While climate change remains the biggest threat to the Great Barrier Reef, pollution, overfishing, and coral depletion are also major concerns.
Overfishing is a critical issue impacting the Great Barrier Reef. Coral reef fish are a significant food source for over a billion people worldwide, and many coastal communities rely on coral reef fisheries for their economic, social, and cultural benefits. However, unsustainable fishing practices can lead to the depletion of key reef species and habitat damage. Rapid human population growth, increased demand, and the use of efficient fishing technologies have exacerbated this problem.
Nearshore habitats serve as nurseries for many fish species. When young fish are caught in nets, they are removed before they can help replenish the population. Additionally, traps set too close to reefs and marine debris, such as lost nets and lines, can damage coral reefs, which take a long time to recover.
Overfishing can also alter the food-web structure and cause cascading effects. For example, a reduction in the number of grazing fish can lead to an increase in algal overgrowth on corals. Blast fishing, or using explosives to catch fish, can cause physical damage to corals. Coral harvesting for the aquarium trade, jewelry, and curios can further deplete specific species, destroy reef habitats, and reduce biodiversity.
Some fish species gather in large numbers at predictable times and locations to mate, making them particularly vulnerable to overfishing. The absence of these large fish means that overall fish populations decline over time.
The combination of overfishing and other stressors, such as pollution and climate change, can decrease the resilience of the reef, making it more susceptible to disease and invasive species. Increased ocean temperatures, changing ocean chemistry, and nutrient pollution create an environment where pathogens can thrive and corals struggle to survive.
To address overfishing and coral depletion, it is essential to implement sustainable fishing practices, improve management and enforcement, and reduce the impact of other stressors on the reef. By ensuring the protection and recovery of the reef's health, we can help maintain the balance of this delicate ecosystem.
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Land-based pollution from development
As human populations expand in coastal areas, the landscape is altered, increasing land-based sources of pollution and threatening coral reef health. Land-based pollution is entirely preventable and controllable.
One of the major sources of land-based pollution is agriculture. The runoff of pollutants from agricultural practices is a major threat to the Great Barrier Reef. Excessive fertiliser applied to crops, such as sugar cane, can wash into rivers and waterways, ultimately reaching the reef. Nitrogen from these fertilisers is linked to harmful algal blooms, which can block sunlight, reducing coral's resilience to bleaching and coral diversity. Pesticides and herbicides have been detected in high concentrations in inshore areas, posing a risk to marine plants and animals.
Another source of land-based pollution is tree clearing and overgrazing of grasslands, which cause soils to erode and wash into creeks and rivers that run into the Great Barrier Reef. Sediment discharged from rivers reduces sunlight available to seagrasses and corals, smothering their growth. Increased sedimentation and nutrients can cause higher algal growth, the build-up of pollutants in sediments and marine species, and reduced light and smothered corals.
To reduce the impact of land-based pollution, individuals can make sustainable choices in their daily lives, such as minimising the use of fossil fuels and single-use plastics. Governments can also play a role by implementing policies to reduce water pollution and improve recycling.
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Frequently asked questions
Water pollution is one of the highest risks to the Great Barrier Reef's health.
Water pollution in the Great Barrier Reef comes from urban runoff, agricultural practices, and improper waste management.
Agricultural pollution can cause algal blooms, which block sunlight and reduce coral's resilience to bleaching. It can also inhibit the growth of seagrass, on which many marine animals depend.
Plastic pollution makes up more than 80% of the marine debris found on the reef. It harms marine life and affects human health as plastic pollution and heavy metals enter the food chain.
Climate change is predicted to increase the frequency and intensity of rainfall, which will cause higher levels of pollutants to enter the Great Barrier Reef.
