Bronte Wells
Coral reefs are some of the most biodiverse ecosystems on Earth, but they are in crisis. Pollution, overfishing, destructive fishing practices, coastal development, and climate change are some of the many ways that humans damage reefs every day. One of the most significant threats to reefs is pollution, which can come from land-based runoff, dredging, coastal development, and sewage treatment plant operations. This runoff may contain sediments, nutrients, chemicals, plastics, and other debris that can smother and kill corals, interfere with their ability to feed and reproduce, and make them more susceptible to disease.
| Characteristics | Values |
|---|---|
| Trash and micro-plastics from improper disposal and stormwater runoff | Plastic bags, bottles, discarded fishing gear, degraded plastics, and microplastics |
| Overfishing | Reduced grazing fish that keep corals clean of algal overgrowth |
| Blast fishing | Dynamite or other heavy explosives |
| Coral harvesting for the aquarium trade, jewelry, and curios | Over-harvesting of specific species, destruction of reef habitat, and reduced biodiversity |
| Increased ocean temperatures | Coral bleaching |
| Changing ocean chemistry | Increasing levels of carbon dioxide dissolved in seawater |
| Land-based sources of pollution | Coastal development, deforestation, agricultural runoff, and oil and chemical spills |
| Failed septic systems | Nutrients and pathogens |
| Stormwater runoff | Sedimentation, toxins, nutrients, and pathogens |
| Climate change | Changing ocean chemistry |
| Air pollution | Stunted growth of coral reefs |
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What You'll Learn
Nutrient pollution
The influx of nutrients causes an increase in algae growth, which blocks sunlight from reaching the corals and consumes the oxygen that corals need for respiration. This process, known as eutrophication, leads to a decrease in water quality and can result in oxygen depletion in the water. The growth of algae can crowd out corals, significantly degrading the coral reef ecosystem. Additionally, the algae can settle on the coral reefs, smothering them and interfering with their ability to feed, grow, and reproduce.
Furthermore, nutrient pollution can support the growth of pathogenic microorganisms, including bacteria, viruses, and fungi. These pathogens, introduced through inadequately treated sewage, stormwater, and runoff, can cause diseases in corals, especially when they are already stressed by other environmental factors. The presence of pathogens, along with household and industrial chemicals, can affect coral reproduction and growth, further exacerbating the impact of nutrient pollution on coral reef health.
The effects of nutrient pollution on coral reefs are far-reaching, disrupting key ecosystem functions and undermining the invaluable services that coral reefs provide, such as shoreline protection and food security for coastal communities. Addressing nutrient pollution is crucial for the conservation and long-term survival of coral reefs.
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Plastic pollution
Plastic waste in the ocean has been shown to carry many bacteria, including pathogens that cause coral disease. A study found that the likelihood of disease in coral reefs increases from 4% in the absence of plastic to 89% when corals are in contact with plastic. Plastic can block sunlight from reaching the coral, and it can also physically damage the coral, creating openings for pathogens to infect the coral. This can lead to the development of coral diseases such as skeletal eroding band, white syndromes, and black band disease.
The Asia-Pacific region is particularly affected by plastic pollution, with nine of the ten countries with the highest levels of mismanaged plastic waste entering the ocean located in this region. A survey of 159 reefs in the region found plastic was a common pollutant, with items such as bottles, diapers, cotton swabs, and food wrappers entangled in the coral. It is estimated that over 11 billion plastic items could be entangled in coral reefs in the Asia-Pacific region.
The impact of plastic pollution on coral reefs highlights the importance of reducing plastic consumption, properly recycling plastic waste, and ensuring that waste does not end up in the environment. By taking action to reduce plastic pollution, we can help protect the biodiversity and economic and ecological value that coral reefs provide.
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Destructive fishing practices
Trawlers also cause severe damage to reefs by dragging nets along the ocean bottom, mowing down everything in their path and leaving long, wide patches of rubble and sand. In addition, certain types of fishing gear can cause serious physical damage to coral reefs, seagrass beds, and other important marine habitats.
Coral reefs are further threatened by overfishing, which can deplete key reef species and damage coral habitats. This can alter the food-web structure and cause cascading effects, such as reducing the number of grazing fish that keep corals clean of algal overgrowth.
Another destructive fishing practice is the use of cyanide, which is toxic to marine life and can harm coral reefs. In addition, the collection of live corals for the aquarium market can damage reefs, as can mining coral for building materials.
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Climate change
Increased Ocean Temperatures
Coral reefs are sensitive to changes in ocean temperature. As atmospheric temperatures rise, so do seawater temperatures. This warming places stress on corals, causing them to expel the microscopic algae that live inside their tissues and produce food for them. This condition is known as coral bleaching, where the loss of algae reveals the white colour of the coral's calcium carbonate structure. Bleached corals are not dead, but they are more vulnerable to starvation, disease, and other threats. Severe or prolonged bleaching can lead to the death of coral colonies.
Ocean Acidification
The ocean absorbs carbon dioxide from the atmosphere, contributing to the process of ocean acidification. The increased acidity of the ocean makes it more difficult for corals to build their skeletons and form coral reefs. This also weakens the protective function of coral reefs for coastlines against storms and waves, which can result in land erosion.
Severe Weather Events
Loss of Habitat
The combination of increased ocean temperatures, ocean acidification, and severe weather events leads to the loss of coral reef habitats. This, in turn, threatens the thousands of marine species that depend on these habitats for survival.
Urgent global action is needed to address climate change and protect coral reefs. Efforts to reduce greenhouse gas emissions, strengthen key ecosystems, and help coral reefs adapt to warmer temperatures are crucial for their conservation.
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Coastal development
One of the primary ways in which coastal development harms coral reefs is through sedimentation. Construction activities, such as building marinas, docks, and bridges, and dredging to replenish beaches, can cause sediment to be deposited onto reefs. This sedimentation can smother corals, interfering with their ability to feed, grow, and reproduce. The excess sediment also reduces the light available to corals, which they need for photosynthesis, and can make them more susceptible to diseases.
Nutrient runoff from land-based activities is another consequence of coastal development that harms coral reefs. Fertilizers, sewage, and inadequate wastewater management can introduce excessive nitrogen and phosphorus into the water. This nutrient enrichment can cause increased acidity in coastal waters, exacerbating the effects of ocean acidification. Ocean acidification reduces the availability of dissolved salts and ions needed by corals to form their calcium carbonate structures, slowing coral and reef growth and potentially leading to the dissolution of coral skeletons.
Additionally, coastal development can lead to physical damage or destruction of coral reefs. Activities such as quarrying, destructive fishing practices, and boat anchors can directly harm coral reefs. Improper waste disposal and stormwater runoff from coastal development can introduce trash and microplastics into the ocean, which can snag on corals, block sunlight, and entangle or damage reef organisms.
The impacts of coastal development on coral reefs underscore the importance of sustainable practices that protect sensitive coral ecosystems. Implementing zoning regulations, increasing the number of Marine Protected Areas, and adopting sustainable development standards are essential steps towards preserving the health of coral reefs and the diverse species that depend on them.
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Frequently asked questions
Plastic pollution has been found to cling to coral reefs, blocking sunlight from reaching them and hindering their ability to photosynthesize. It also increases the likelihood of disease in corals from 4% to 89%. Plastic can also abrade corals, creating openings for pathogens to enter and infect the coral.
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.
Destructive fishing practices, such as using dynamite or cyanide, can cause physical damage to coral reefs. Additionally, abandoned fishing nets and gear, often called "ghost nets", can entangle and kill reef organisms, as well as break or damage coral structures.
