Kiera Jefferson
Coral reefs are one of the most important ecosystems in the world, supporting a quarter of all marine species, protecting coastlines, and driving local economies. However, human activities have put these ecosystems in jeopardy. While climate change is the primary factor disrupting coral reefs, air pollution from land-based sources also plays a significant role in their destruction. This includes coastal development, deforestation, agricultural runoff, and oil and chemical spills, which can impede coral growth, disrupt ecological function, and cause disease and mortality in sensitive species. Additionally, plastic pollution, overfishing, and physical damage from ships and divers further contribute to the degradation of coral reefs.
| Characteristics | Values |
|---|---|
| Coral reefs affected by air pollution | Global coral reefs |
| Primary causes of coral reef degradation | Climate change, pollution, physical damage |
| Coral reefs affected by physical damage | The Great Barrier Reef in Australia |
| Coral reefs affected by pollution | Pacific coral reefs, Caribbean coral reefs, Florida Keys, Northwestern Hawaiian Island reefs, U.S. Virgin Islands reefs, Pearl and Hermes Atoll |
| Coral reefs affected by climate change | Global coral reefs, National Marine Sanctuary of American Samoa |
| Human activities causing coral reef degradation | Burning fossil fuels, overfishing, coastal development, deforestation, agricultural runoff, oil and chemical spills, coral mining, coral reef fisheries, coral bleaching |
| Impact of pollution on coral reefs | Impedes coral growth and reproduction, disrupts ecological function, causes disease and mortality in sensitive species, decreases oxygen, increases nutrients, enhances algal growth, interferes with coral feeding and reproduction, introduces pathogens |
| Impact of physical damage on coral reefs | Breaking coral, coral mining, stepping on coral, dropping anchors |
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What You'll Learn
Plastic pollution and debris
Plastic pollution is an emerging threat to coral reefs, causing widespread damage. A recent study found that plastic debris was present on 92% of the reefs examined, including some of the most remote and uninhabited ones. Plastic waste can smother and kill corals, sponges, and other invertebrates, and it also increases the likelihood of coral disease.
The impact of plastic pollution on coral reefs is twofold. Firstly, plastic debris can cause physical damage to coral tissue, leading to infection by bacteria present on the plastic. Secondly, plastic can carry pathogens, including coral pathogens, and promote their spread between reefs, increasing the risk of disease transmission. This is particularly concerning given that corals are already vulnerable to bleaching and disease due to unusually warm water temperatures.
The sources of plastic pollution in coral reefs vary. Land-based sources include waste from cities, landfill sites, beach litter, industrial and sewage discharge, and personal care products. Sea-based sources include lost or abandoned fishing gear, such as nets, ropes, and lines, which can become entangled in coral reefs and continue to trap and kill marine animals even after being discarded—a phenomenon known as "ghost fishing." Plastic pollution is denser near cities and markets, and low and middle-income countries tend to have higher levels of plastic pollution due to limited resources for waste management.
Microplastics, in particular, are one of the leading pollutants on the earth's surface and are found in aquatic environments. The excessive production and unscientific disposal of microplastics have severely impacted marine ecosystems, including coral reefs. The ingestion of microplastics by coral polyps has hindered coral growth and contributed to coral bleaching.
To address the issue of plastic pollution in coral reefs, it is essential to reduce plastic consumption, improve recycling practices, and ensure proper waste management, especially in low and middle-income countries. Additionally, the existing national, regional, and international policies regarding marine debris need to be strengthened, and collaboration is key to finding solutions to this global problem.
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Climate change and ocean warming
Coral reefs are in decline globally, and climate change is the primary factor disrupting them. The burning of fossil fuels has been the main driver of ocean warming since the 1970s. From 1992 to 2019, the total heat stored by the oceans rose by 187 zettajoules, and most corals cannot survive in warmer waters.
When corals are stressed by environmental changes, such as ocean warming, they expel their zooxanthellae, revealing their white skeletons in a process called bleaching. Bleached corals are more vulnerable to additional stressors, and with climate change, the frequency of marine heatwaves is increasing, leaving corals with insufficient time to recover. As a result, thousands of marine creatures lose their habitat.
Furthermore, ocean warming is causing coral skeletons to dissolve. Increases in ocean acidity (lower pH values) reduce the availability of dissolved salts and ions necessary for corals to form their calcium carbonate structures. Consequently, coral and reef growth slows, and some species are more affected than others.
In addition to climate change, other human activities contribute to coral reef decline. Pollution, including chemicals, fertilizers, and toxins, travels from the land into the ocean, affecting coral reefs. For example, excess nutrients from agricultural and residential fertilizer use can lead to increased algae growth, blocking sunlight and consuming oxygen needed by corals for respiration. Sedimentation from coastal development and agriculture can smother corals, interfering with their ability to feed, grow, and reproduce.
To protect coral reefs, it is essential to address climate change and reduce ocean warming. This includes reducing carbon emissions and transitioning away from fossil fuels to mitigate the impacts of climate change on coral reefs and the marine ecosystems that depend on them.
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Land-based pollution
Coastal development, such as dredging, quarrying, and coastal construction, can directly damage coral reefs and increase sedimentation. Sediment deposited on reefs can smother corals, interfering with their ability to feed, grow, and reproduce. Additionally, nutrients from agricultural and residential fertilizer use, sewage discharges, and animal waste can result in poor water quality. Excess nutrients can lead to enhanced algal growth, crowding out corals and degrading the ecosystem.
Agricultural runoff and deforestation can also introduce toxicants and pathogens into coral reef ecosystems. Inadequately treated sewage, stormwater, and runoff from livestock pens can contain bacteria and parasites that cause disease in corals, especially when stressed by other environmental conditions. Furthermore, oil and chemical spills can contaminate reefs, harming marine life and disrupting ecological balance.
Plastic pollution is another significant threat to coral reefs. Plastic waste can introduce bacteria that infect corals, and the presence of plastic debris can block the sunlight needed for coral growth. Derelict fishing nets and gear, often referred to as "ghost nets," can entangle and kill reef organisms, damaging reefs even in remote locations.
The impacts of land-based pollution on coral reefs are far-reaching. Coral reefs support a vast array of marine life, protect coastlines during storms, and contribute to local economies through fisheries and tourism. However, human activities, including land-based pollution, are endangering these valuable ecosystems. Scientists emphasize the urgency of intensifying efforts to protect and preserve coral reefs before their existence is jeopardized.
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Overfishing and physical damage
Overfishing is a significant threat to coral reefs. When herbivorous fish that feed on algae are overfished, it can lead to uncontrolled algae growth, which eventually smothers the corals. Overfishing can also alter the food-web structure, causing cascading effects such as a reduction in the number of grazing fish that keep corals free of algal overgrowth. This disruption to the delicate food web of coral reef ecosystems can lead to an overabundance of algae, which can smother and kill corals.
Destructive fishing practices, such as deep-water trawling, blast fishing, and the use of explosives and cyanide, directly destroy coral structures and indiscriminately kill marine life. Blast fishing, for example, can destroy 64 square feet (5.9 square meters) of reef with a single blast. Cyanide fishing, initially used to stun fish for aquariums, is now also used for food. Dynamite fishing not only destroys the coral but the resulting shockwaves can kill surrounding marine organisms.
Coral reefs are also vulnerable to physical damage from coastal development, including dredging, quarrying, and the construction of ports and harbors. This development results in erosion, and the excess sediment from runoff can block the light that zooxanthellae need to survive, causing further harm to the coral. Boat anchors and groundings can also inflict physical damage on reefs.
Irresponsible recreational activities, such as touching or removing corals, contribute to the destruction of coral reefs. Even minor acts like touching a coral can strip away their protective mucus layers, exposing them to infection. Additionally, the demand for live corals for the aquarium trade and the mining of corals for building materials further exacerbates the threat, directly reducing the size and complexity of reef ecosystems.
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Nutrient run-off and eutrophication
Coral reefs are in decline in the US and worldwide, and human activities are a major cause of this. Land-based sources of pollution, such as coastal development, deforestation, agricultural runoff, and oil and chemical spills, can impede coral growth and reproduction, disrupt overall ecological function, and cause disease and mortality in sensitive species.
In addition to nutrient run-off, other forms of pollution, such as plastic debris and abandoned fishing gear, can also entangle and kill reef organisms, breaking and damaging reefs. Climate change is another significant threat to coral reefs, as rising ocean temperatures and acidity levels can slow coral growth and even dissolve coral skeletons.
The preservation of coral reefs requires a combination of education, intensified protection efforts, and the mitigation of land-based pollution sources. Regional nutrient management is crucial for reef survival, and understanding the complex interactions between nutrient pollution, pH levels, and other stressors is essential for developing effective conservation strategies.
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Frequently asked questions
It is difficult to determine the exact number of coral reefs that are destroyed due to air pollution, as it is a combination of air pollution and other factors that lead to their destruction. Air pollution, such as carbon emissions, contributes to climate change, which is the primary cause of coral reef disruption.
Air pollution, particularly carbon emissions, contributes to climate change, which causes ocean warming and acidification. Ocean warming leads to coral bleaching, where stressed corals expel their zooxanthellae, revealing their white skeletons. Bleached corals are more vulnerable to diseases and storms, and if the frequency of marine heatwaves is high, they may not have enough time to recover. Ocean acidification reduces the availability of dissolved salts and ions, which corals need to form their calcium carbonate structure, thus slowing or preventing their growth.
Coral reefs are vulnerable to various other human activities, including overfishing, physical damage from ships and divers, coastal development, dredging, quarrying, and destructive fishing practices and gear. Additionally, land-based sources of pollution, such as agricultural runoff, sewage discharge, and oil and chemical spills, can also harm coral reefs by impeding their growth and reproduction and causing diseases.
