Pollution's Deadly Impact On Coral Ecosystems

Coral reefs are some of the most biodiverse ecosystems on the planet, but they are in crisis. Pollution is a significant contributor to the decline of coral reefs. Land-based activities such as coastal development, deforestation, and agricultural runoff introduce toxicants, sediments, nutrients, chemicals, insecticides, oil, and debris into the ocean. This form of pollution can cause coral disease, hinder coral growth and reproduction, and even lead to coral mortality. Plastic pollution, in particular, has been identified as a significant stressor, with plastic waste entangled in coral reefs causing abrasion and increasing the likelihood of disease. Climate change, influenced by human activities, also plays a crucial role in coral bleaching, as even small increases in water temperature can trigger corals to expel their symbiotic algae, resulting in a loss of colour and, eventually, their death.

Climate change and rising water temperatures

As the ocean absorbs heat, it also takes in carbon dioxide from the atmosphere, leading to ocean acidification. This process reduces the availability of dissolved salts and ions necessary for corals to form their calcium carbonate structures. Consequently, coral growth slows, and if acidification becomes severe, coral skeletons may even dissolve. The increase in carbon dioxide has caused ocean acidity to rise by about 30% since the Industrial Revolution, and it is expected to increase by another 40% by the end of this century.

Rising water temperatures cause coral bleaching, which occurs when stressed corals expel the microscopic symbiotic algae zooxanthellae from their tissues. These algae provide the coral with its colour and are their primary food source. Without the algae, the white colour of the underlying calcium carbonate structure is revealed, and the coral is left more vulnerable to additional stressors, including infectious diseases. While bleached coral does not immediately die, it becomes less resilient and is more susceptible to mortality.

The frequency of marine heatwaves is increasing due to climate change, leaving corals with insufficient time to recover between stressful events. As a result, the risk of coral mortality increases, and the loss of coral reefs has devastating consequences for the thousands of marine species that depend on them for survival. According to the "Status of Coral Reefs of the World 2020" report, a global dataset analysis spanning from 1978 to 2019, a 70-90% decrease in live coral on reefs is predicted by 2050 without drastic action to limit global warming.

Plastic pollution

Secondly, plastic pollution promotes the development of diseases in coral reefs. Studies have shown that the presence of plastic trash increases the likelihood of coral reefs contracting diseases such as skeletal eroding disease, white syndrome, and black band disease, which can lead to rapid coral mortality. While the exact mechanisms are still being studied, it is believed that plastic debris carries pathogens and bacteria, facilitating their spread between reefs and elevating the risk of infection. Additionally, plastic pollution may block sunlight from reaching the coral, leading to low-oxygen conditions that further encourage the growth of disease-causing bacteria.

Microplastics, tiny plastic particles of 5mm or less, pose a significant threat to coral reefs. These particles can constantly rub against corals due to wave and current action, causing physical abrasion. Moreover, corals may ingest microplastics, leading to a false sense of fullness and subsequent malnutrition, as well as potential blockages and internal damage to their digestive systems. Microplastics can also absorb and transfer toxic chemicals and pollutants to corals, further compromising their health and survival.

The impact of plastic pollution on coral reefs is not limited to direct physical and biological effects. Plastic pollution is often indicative of broader environmental challenges, such as inadequate waste management practices and the excessive use of single-use plastics. These issues can have far-reaching consequences for coral reefs and the ecosystems they support. Additionally, plastic pollution can have economic implications, as activities related to coral reefs contribute significantly to local economies through tourism, fishing, and other industries.

The magnitude of the problem is evident in studies and surveys. A four-year study in the Pacific Ocean found plastic pollution, including bags, bottles, diapers, and wrappers, causing widespread damage to reefs from Thailand to Australia. Another survey of 159 reefs near Southeast Asian and Australian countries examined over 124,000 corals, finding that the presence of plastic increased the risk of disease from 4% to 89%.

Sewage and runoff

Furthermore, sewage and runoff can introduce pathogens, bacteria, and parasites into the water, which can cause coral diseases, especially in ecosystems that are already stressed by other factors. For example, sewage runoff containing inadequately treated human waste can introduce bacteria and parasites that cause diseases in corals. Similarly, agricultural runoff can contain pesticides and herbicides that are toxic to corals, affecting their reproduction, growth, and feeding abilities.

Plastic pollution is another significant concern, as plastic waste can abrade and tear open the skin of corals, providing an entry point for infections and increasing the likelihood of disease. Plastic debris can also block sunlight, hindering the coral's ability to photosynthesize and carry out essential functions.

The impact of sewage and runoff pollution on coral reefs is far-reaching, contributing to coral disease, bleaching, and even coral mortality. It is essential to address these issues through proper waste management, reduced fertilizer use, and the protection and restoration of coral reef ecosystems.

Destructive fishing practices

Overfishing is another destructive fishing practice that alters food-web structures and causes cascading effects, such as a reduction in grazing fish that control algal growth on corals. This can lead to overgrowth, smothering the corals and interfering with their ability to feed, grow, and reproduce. The removal of top-level predators through overfishing can also have a cascading effect on the entire ecosystem, as fewer fish are left to perform their ecological functions.

Fishing for coral, whether for the aquarium trade, jewelry, or curios, can lead to over-harvesting of specific species, destruction of reef habitats, and reduced biodiversity. The aggregate effects of these stressors decrease the overall resilience of the reef, making it more susceptible to disease and invasive species.

In addition to these legal fishing activities, illegal techniques, such as the use of chlorine bleach and other poisons, further endanger coral reefs and can cause human health issues.

The increasing human activities and the desire for fish as a source of food and recreation have placed immense pressure on coral reefs, threatening their existence and recovery.

Coastal development

One of the main ways in which coastal development harms coral reefs is through physical damage or destruction. This can include dredging, quarrying, and the use of destructive fishing practices and gear, such as deep-water trawling and blast fishing. Boat anchors and groundings, as well as reckless tourism, can also cause physical damage to coral reefs. For example, careless divers may trample on corals or break off pieces as souvenirs. Additionally, the removal of coral for the aquarium trade, jewelry, and curios can lead to over-harvesting, habitat destruction, and reduced biodiversity.

Another major impact of coastal development on coral reefs is sedimentation. Soil runoff from shoreline construction and upland activities can smother corals, interfering with their ability to feed, grow, and reproduce. This can be further exacerbated by the loss of coastal wetlands, such as mangrove forests, which normally serve as buffer zones that absorb excess nutrients, sediments, and pollutants from coastal runoff.

Nutrient-rich runoff from improperly treated sewage, agriculture, and mariculture can also increase algae growth, leading to overgrowth that smothers corals. Industrial effluents, agricultural and urban runoff, and trash and microplastics from improper disposal can further pollute coastal waters, poisoning reef communities.

To address these issues, it is crucial to promote sustainable practices and conservation efforts. This includes implementing integrated coastal management plans that minimize the potential impact of human activities, such as urban infrastructure, industry, agriculture, and tourism, on coral reefs. Supporting businesses that offer greener and cleaner technologies for coastal development is also essential. Additionally, it is important to strengthen the role of non-governmental organizations and local communities in planning and implementation processes to ensure the protection of these valuable ecosystems.

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