Pollution's Impact On The Great Barrier Reef

The Great Barrier Reef, the largest living structure on Earth, is under threat from pollution. Stretching along Australia's northeastern coast, the reef is affected by land-based activities such as agriculture, deforestation, and coastal development. Water pollution from these sources is considered one of the highest risks to the reef's health, impacting critical habitats for threatened species such as dugongs, turtles, and fish. The main water quality issues include increasing sediment, nutrients, and contaminants entering coastal waters, which can smother and reduce the light available for coral growth. Additionally, nutrient runoff has been linked to outbreaks of crown-of-thorns starfish, which contribute significantly to the loss of coral cover. Climate change, including rising sea temperatures and ocean acidification, further exacerbates these issues.

Land-based sources of pollution

The Great Barrier Reef is a natural wonder that stretches along Australia's northeastern coast, forming the largest living structure on Earth. Unfortunately, this vast network of coral reefs and atolls is under threat from land-based sources of pollution, which have far-reaching impacts on the delicate reef ecosystem.

One significant contributor to the problem is agricultural runoff. Farming activities, such as the overuse of fertilisers and pesticides, result in increased nutrient levels in the water. This, in turn, stimulates excessive growth of algae, which blocks sunlight and reduces the resilience of corals, making them more susceptible to bleaching. The algae also compete with corals for space, hindering their growth and survival. Additionally, pesticides and herbicides detected in high concentrations in the World Heritage Area pose risks to marine plants and animals, including the sensitive species that depend on the reef.

Deforestation and tree clearing in the catchment areas of the Great Barrier Reef are another concern. The removal of trees leads to widespread erosion, as their roots are no longer there to secure the topsoil. Torrential rains then carve deep gullies, washing massive amounts of sediment into the rivers and, eventually, out onto the reef. This sedimentation further reduces the clarity of the water, restricting the growth of light-dependent plants and animals, including corals.

Other land-based sources of pollution include urban and industrial activities, sewage treatment plants, aquaculture, mining, ports, and defence activities. These contribute a range of pollutants, such as petroleum hydrocarbons, marine debris, microplastics, pharmaceuticals, and personal care products, which all have detrimental effects on the reef's ecosystems.

The impact of these land-based sources of pollution is far-reaching, impeding coral growth and reproduction, disrupting ecological functions, and causing disease and mortality in sensitive species. It is important to address these issues through improved land management practices, changes to regulations, and targeted interventions to reduce the flow of pollutants into the reef and give it a chance to recover and regenerate.

Climate change

The Great Barrier Reef is one of the most complex natural ecosystems on the planet. Climate change is the single biggest threat to the future of the Great Barrier Reef and coral reefs worldwide.

Rising Temperatures

Coral Bleaching

The rise in ocean temperatures causes heat stress in corals, leading to coral bleaching. When corals are stressed by high temperatures, they expel the microscopic algae that live inside their tissues, revealing their white skeletons. Bleached corals are not dead, but they are more susceptible to starvation and disease. Marine heatwaves have already triggered four mass coral bleaching events on the Great Barrier Reef in just seven years, reducing shallow water coral reefs by up to 50%. While coral reefs can recover from bleaching over time, this is only possible if temperatures drop and conditions return to normal.

Ocean Acidification

The ocean absorbs about 30% of the carbon dioxide generated by humans, making the water more acidic. This process is known as ocean acidification and has decreased the ocean's pH level since the late 18th century. A more acidic ocean reduces the ability of corals to build skeletons and form coral reefs. Reefs provide crucial protection to coastlines from storms and serve as habitats for thousands of marine species.

Severe Weather Events

Marine Species Displacement

As water temperatures rise, many marine species are being forced to move towards cooler habitats. This displacement creates increased competition for food and shelter in the cooler waters, threatening the entire ecosystem. The loss of marine life can have devastating consequences for local ecosystems, food sources, and industries such as tourism.

Addressing Climate Change

To protect the Great Barrier Reef and other coral reef ecosystems, urgent global action is needed to drastically reduce greenhouse gas emissions. This includes strengthening key ecosystems like seagrass meadows, mangroves, and wetlands, which play a vital role in absorbing carbon dioxide and combating climate change. While emission reduction is crucial, it is no longer sufficient to guarantee the survival of coral reefs. Additional interventions are necessary to help coral reefs adapt to the warmer temperatures already caused by climate change.

Water quality

The Great Barrier Reef is a spine of 3,800 reefs and atolls stretching along Australia's northeastern coast. It is the largest living structure on Earth. However, the health of the reef is threatened by poor water quality caused by land-based activities, including agriculture, industry, and urban development.

Water pollution is one of the highest risks to the Great Barrier Reef, impacting critical habitats for threatened dugongs, turtles, and fish. The main water quality issues include increasing levels of sediment, nutrients, and contaminants in coastal waters. These pollutants come from agricultural activities, such as excessive fertiliser use and pesticide application, as well as industrial and urban land uses.

Agricultural runoff is a significant contributor to poor water quality in the Great Barrier Reef. Excessive fertiliser use, particularly on sugarcane crops, can lead to increased nitrogen levels in the water, promoting harmful algal blooms. These blooms block sunlight, reducing the resilience of corals to bleaching and decreasing coral diversity. Additionally, pesticides and herbicides used in agriculture have been detected in high concentrations in inshore areas, posing risks to marine plants and animals, including seagrasses, which are a vital food source for dugongs, turtles, and fish.

Deforestation and tree clearing in the catchment areas of the Great Barrier Reef also contribute to water quality issues. Without tree roots to secure the topsoil, erosion occurs, washing an estimated 17 million tonnes of sediment each year into the rivers and, eventually, out onto the reef. This sedimentation reduces light availability, smothering coral and seagrass growth and hindering their ability to photosynthesise.

The combination of increasing sediment, nutrients, and contaminants in the water, along with rising sea temperatures and ocean acidification, is damaging the reef. These factors reduce the resilience of the coral reefs and the ecosystems they sustain.

To address these water quality issues, the Australian Government's Reef 2050 plan aims for an 80% reduction in river nutrient loads by 2025. Additionally, the Queensland government passed a bill in 2019 to improve water quality flowing into the reef from agricultural properties. These efforts are crucial for protecting the health and resilience of the Great Barrier Reef and the industries it supports, such as tourism, fishing, and research.

Crown-of-thorns starfish outbreaks

The Crown-of-thorns starfish (COTS) is a large echinoderm covered in thorn-like spikes that preys upon coral. While it is native to the Indo-Pacific region, including the Great Barrier Reef, the starfish has been described as invasive due to its dense populations and the devastation it causes. COTS outbreaks can cause widespread damage to the reef, including the loss of coral cover and a decline in biodiversity. Nearly half of the reef's coral died between 1985 and 2012, and approximately 42% of this decline can be attributed to COTS outbreaks.

COTS feed on coral by extruding their stomachs from their bodies, wrapping them around the coral, and digesting their tissues. An adult COTS can consume up to 10 square metres of coral per year and can live up to nine months without eating. During an outbreak, when 15 or more COTS are found in a one-hectare area, they can strip a reef of up to 90% of its living coral tissue. COTS breed through spawning, with females releasing over 200 million eggs per year. The resulting larvae feed on phytoplankton before metamorphosing into their juvenile form.

There are two main hypotheses for the environmental triggers of COTS outbreaks: the predator removal hypothesis and the terrestrial runoff hypothesis. The predator removal hypothesis states that the population of COTS has increased due to the overfishing of its predators. The proposed solution is a commercial fishing ban that establishes "no-take" regions. The terrestrial runoff hypothesis proposes that increased nutrient levels in the water from runoff or rainfall events have led to denser phytoplankton populations, enhancing larval survival and resulting in more adult COTS.

Efforts to reduce and control the COTS population are vital to the survival of the Great Barrier Reef. On the Great Barrier Reef, targeted COTS control programs are used, with trained divers injecting the starfish with bile salts or vinegar to kill them without harming the surrounding ecosystem. The COTSbot, an autonomous vehicle programmed to patrol the reef and inject COTS with a lethal dose of bile salts, is also being used to combat the outbreaks.

The impacts of COTS outbreaks on the Great Barrier Reef highlight the complex ecological challenges facing this natural wonder and the urgent need for effective management and conservation strategies.

Coastal development

Agriculture is the most extensive land use in the Great Barrier Reef catchment, with cattle grazing being the most common. Over 80% of the catchment area is used for some form of agriculture, including crops, dairy, and horticulture. This has resulted in the broad-scale clearing of habitats, which has negatively impacted the health of the reef. Furthermore, agriculture is the main source of pollution affecting the inshore marine ecosystem, with pesticides and nutrients from runoff polluting the water that flows into the reef's lagoon.

Urban and industrial development, while occupying a small proportion of the catchment area, also contribute to the degradation of the reef. This includes the construction of housing, roads, drainage systems, commercial and light-industry areas, and tourism facilities. Poor planning and fast-tracking of some tourism developments, such as Port Hinchinbrook, have resulted in ecological damage. Additionally, the modification of coastal ecosystems for urban and industrial development can impact the health of seagrass meadows, which are important feeding and breeding grounds for turtles and dugongs.

Mining operations have also played a role in the decline of the Great Barrier Reef. Queensland is associated with some of the world's largest mines and coal ports, with coal production more than doubling since the early 1990s. Curtis Island, located off the coast of Queensland, is the site of the world's first project to convert coal seam gas to liquefied natural gas.

Port development has been a major driver of coastal reclamation, infilling areas of the ocean, wetlands, and other water bodies along the Great Barrier Reef coast. This has resulted in the reclamation of approximately eight square kilometres of land within the World Heritage Area since 1981, with Gladstone being the most affected region. Port development can also create artificial barriers to freshwater flow, further impacting the health of the reef.

Overall, the effects of coastal development have had a cumulative impact on the Great Barrier Reef, endangering its beauty, biological richness, and cultural values.

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