Water Pollution's Impact: Coral Reefs In Danger

Water pollution poses a significant threat to coral reefs, which occupy less than 1% of the ocean floor yet support an astonishing 25% of all marine species. The leading causes of water pollution affecting coral reefs include untreated sewage, agricultural runoff, plastic pollution, and oil and chemical spills. These contaminants degrade water quality, disrupt ecological functions, impede coral growth and reproduction, and increase the prevalence of diseases among coral reefs. With coral reefs already facing the challenges of climate change and ocean acidification, addressing water pollution is crucial for the preservation of these invaluable ecosystems.

Plastic pollution

One of the main ways plastic pollution harms coral reefs is by physically damaging the coral structures. As plastic items move across and around the coral, they can scrape and abrade the coral surface, causing tissue loss similar to a wound on human skin. This not only weakens the coral structurally but also creates openings for pathogens and infections to enter. A study of 338 corals exposed to plastic fishing gear found that 69% of them exhibited physical damage, with 62% showing fresh tissue loss.

Another way plastic pollution impacts coral reefs is by blocking sunlight from reaching the coral. This can inhibit the coral's ability to photosynthesize and grow, further weakening the reef. Additionally, microplastics adhering to coral tissue could be impairing the corals' growth and health by preventing them from capturing prey or causing them to expend energy removing the microplastics.

The risk of disease is significantly higher in reefs polluted by plastic. Studies have found that corals in contact with plastic have an increased risk of developing diseases such as skeletal eroding band, white syndromes, black band, growth anomalies, brown band, and atramentous necrosis. The presence of plastic debris promotes the development of these diseases, with the risk of disease up to 22 times greater on polluted reefs compared to preserved reefs.

The impact of plastic pollution on coral reefs is not limited to direct physical damage. Plastic waste can also indirectly harm reefs by breaking down into microplastics and nanoplastics, which can be ingested by marine life, including reef megafauna such as sharks, manta rays, dolphins, and whales. These microplastics can then enter the food chain and have ecosystem-level impacts.

To mitigate the effects of plastic pollution on coral reefs, it is essential to reduce plastic consumption, properly recycle plastic waste, and improve waste management practices, especially in low and middle-income countries that may lack the necessary resources. Banning single-use plastic items, such as plastic bags, and encouraging the use of reusable alternatives can also significantly reduce the plastic pollution that threatens coral reefs.

Eutrophication

One of the primary impacts of eutrophication is the promotion of "nuisance" algal growth. The elevated nutrient levels, especially nitrogen, fuel the proliferation of algae, which then blocks sunlight and consumes oxygen needed by corals for respiration. This disruption of light and oxygen availability causes stress to coral polyps and their algal symbionts, affecting their physiological performance and overall health.

Additionally, eutrophication exacerbates the problem of marine debris. As eutrophication fuels the growth of algae and other organisms, abandoned fishing gear, also known as "ghost nets," can become entangled with the increased marine life. This entanglement not only damages and kills reef organisms but also contributes to the accumulation of debris within the coral reef ecosystem.

The impacts of eutrophication on coral reefs are complex and far-reaching. The increased nutrient levels disrupt the natural balance of the ecosystem, leading to algal growth that competes with corals for resources. This, in turn, can initiate a chain reaction of events, including changes in species composition, food web disruptions, and the exacerbation of marine debris issues. Understanding and managing eutrophication are crucial steps in preserving the delicate coral reef ecosystems and ensuring their long-term survival.

Marine debris

Derelict (abandoned) fishing nets and other gear often called "ghost nets" because they still catch fish and other marine life despite being abandoned, can entangle and kill reef organisms and break or damage reefs. Hard corals, like the kind that form reefs, can become entangled in abandoned or lost fishing nets. As floating nets become snagged on branches, they can break or scratch the coral, leaving big scars on the reef.

The world's increasing number of marine debris is primarily due to the growing human population. Land-based and sea-based sources both contribute significantly to the production of marine debris, with 90% of this debris entering aquatic systems annually from land-based sources. The Northwestern Hawaiian Island reefs are particularly prone to the accumulation of marine debris because of their central location in the North Pacific gyre. Natural disasters such as hurricanes, tropical storms, tsunamis, and landslides have the potential to be the source of a tremendous amount of marine debris.

Oil and chemical spills

Oil spills are a significant threat to coral reefs, with the main oil transport routes in the oceans close to important coral reefs. Coral reefs are vulnerable to contamination by oil spills, and the widespread use of petroleum products means that offshore oil and gas production has increased the risk of accidents in marine environments.

Oil spills can affect corals in several ways, depending on the species and maturity of the coral, as well as the level and duration of exposure to oil. Oil floating on the water's surface can be deposited directly onto corals at low tide, or rough seas can mix oil into the water column, where it can drift down to coral reefs. Even small amounts of oil over an extended period can be harmful to corals.

Oil spills can introduce toxins to the coral reefs, and the use of chemical dispersants to remediate oil pollution can be more harmful to corals than the oil itself. However, studies have shown that using probiotic and oil-degrading microorganisms can improve the health of corals under stress from oil exposure and foster coral survival. This approach is environmentally friendly and sets the stage for improved strategies to protect coral reefs.

In addition to oil spills, chemical spills can also impact coral reefs. For example, pesticides can interfere with coral reproduction and growth. Sewage discharge and stormwater runoff may introduce pathogens into coral reef ecosystems, causing diseases such as white pox.

Climate change

Coral reefs are indispensable ecosystems, occupying less than 1% of the ocean floor yet supporting around 25% of all marine species. They are also vital for humans, providing billions annually through tourism, fisheries, and safeguarding coastal areas.

However, reefs are highly vulnerable to the effects of human activities, both directly and indirectly. Climate change is a significant threat to coral reefs, with rising sea temperatures and ocean acidification causing coral bleaching and weakening coral skeletons, making them susceptible to disease and death.

Coral reefs are sensitive to changes in ocean temperature, and as atmospheric temperatures rise, so do seawater temperatures. This warming stresses the corals, causing them to expel the microscopic algae that live within them and provide them with nutrition and colour. This condition, known as coral bleaching, leaves the white skeletons of the coral exposed. If the algae do not return, the coral will eventually die.

Additionally, the oceans absorb a significant amount of human-made carbon dioxide from the air, leading to increased ocean acidification. This reduces the availability of dissolved salts and ions needed by corals to form their calcium carbonate structures. As a result, coral and reef growth slow down, and if acidification becomes severe, coral skeletons may even dissolve.

The combination of climate change and other human activities has led to mass coral death. Scientists predict that we could lose over 90% of our coral reefs by 2050 if urgent action is not taken to reduce greenhouse gas emissions. This includes curbing carbon emissions, improving wastewater treatment infrastructure, enforcing stricter regulations on wastewater discharges, and fostering better waste management practices.

Frequently asked questions