Pollution's Impact On Coral Health: Understanding The Threats

Coral reefs are in decline globally, and many scientists believe their existence is in jeopardy unless we intensify our conservation efforts. Human activities have a detrimental impact on coral reefs, and pollution is a significant threat to their health. Land-based sources of pollution, such as toxicants, sediments, nutrients, and pathogens, can cause disease and mortality in coral reefs, as well as disrupt their ecological functions and impede their growth and reproduction. This paragraph introduces the topic of pollution's impact on coral health, which will be further explored by examining the various forms of pollution that affect coral reefs and the subsequent consequences.

Sedimentation

Management actions that address local-scale stressors, such as sedimentation, can rapidly improve water quality and reef ecosystem conditions.

Nutrient pollution

One of the primary sources of nutrient pollution is the use of agricultural and residential fertilisers, as well as sewage discharges and animal waste. These sources introduce high levels of nitrogen and phosphorus into coastal waters. While these nutrients are generally beneficial for marine life, corals have adapted to thrive in low-nutrient environments. When there is an excess of nutrients, it can lead to the rapid growth of algae, which blocks sunlight and consumes the oxygen that corals need for respiration. This imbalance can affect the entire coral ecosystem, and excess nutrients can also encourage the growth of harmful microorganisms, such as bacteria and fungi, that can be pathogenic to corals.

Additionally, nutrient pollution can directly influence the growth and physiology of corals and other reef organisms. Excess nutrients can increase competition between endosymbionts and the coral host, reducing growth rates in many coral species. It can also increase bioerosion rates, sediment dissolution, and the growth of fleshy macroalgal species, which can compete with or overtake corals.

The impacts of nutrient pollution on coral reefs highlight the delicate balance of these ecosystems and the need to address human activities that contribute to this issue. By understanding the complex interactions between nutrient pollution and coral health, scientists and conservationists can work towards mitigating these threats and protecting coral reefs for future generations.

Toxic substances

Pesticides, for example, can affect coral reproduction, growth, and other physiological processes. Herbicides, in particular, can damage the symbiotic relationship between coral and algae, resulting in coral bleaching. This occurs when stressed corals expel the microscopic algae that live inside them, revealing the white colour of the underlying calcium carbonate structure. Metals such as mercury and lead, and organic chemicals such as polychlorinated biphenyls (PCBs), oxybenzone, and dioxin, are also suspected of affecting coral reproduction, growth rate, feeding, and defensive responses.

Toxic chemicals found in sunscreen and other personal health products have also been found to threaten coral reefs. Oxybenzone, for example, has been found to accumulate in coral tissues, inducing bleaching, damaging DNA, deforming young corals, and even killing them. Other chemicals found in sunscreen that can harm marine life include benzophenone-1, benzophenone-8, OD-PABA, 4-methylbenzylidene camphor, 3-benzylidene camphor, nano-titanium dioxide, nano-zinc oxide, octinoxate, and octocrylene.

In addition to the toxins mentioned above, other toxic substances that can affect coral health include:

• Nutrient pollution (nitrogen and phosphorus) from agricultural and residential fertiliser use, sewage discharges, and animal waste. This can lead to excess nutrient levels, causing an imbalance in the coral ecosystem and supporting the growth of pathogenic microorganisms.
• Pathogens from inadequately treated sewage, stormwater, and runoff from livestock pens, which can cause disease in corals, especially when they are already stressed by other environmental conditions.
• Trash and microplastics from improper disposal and stormwater runoff, which can block sunlight needed for photosynthesis, entangle and kill reef organisms, and damage corals. They can also be consumed by coral and other marine life, blocking their digestive tracts and introducing toxins.
• Oil and chemical spills, which can cause toxins to enter the water and harm coral health.

Physical damage

Coral reefs are extremely valuable, contributing about $10 trillion a year globally and more than $3 billion a year to the domestic economy. They are also a source of food, livelihoods, and cultural practices for hundreds of millions of people.

Coral reefs are in decline, and their very existence may be in jeopardy unless we intensify our efforts to protect them. One of the main threats to coral reefs is physical damage.

Coastal Development

Coastal development can cause physical damage to coral reefs through dredging, quarrying, and the destruction of natural habitats. This can include activities such as land reclamation, the construction of ports and marinas, and the building of coastal infrastructure. These activities can result in the direct destruction of coral reefs and their habitats, as well as increased sedimentation and pollution that can smother and harm corals.

Destructive Fishing Practices and Gear

Some fishing practices and gear can cause significant physical damage to coral reefs. Destructive fishing methods such as blast fishing, dynamite fishing, and cyanide fishing can directly harm and kill corals. Additionally, the use of certain types of fishing gear, such as bottom trawls and gillnets, can result in the entanglement and destruction of coral reefs.

Boat Anchors and Groundings

Boat anchors that are carelessly dropped or improperly secured can cause extensive physical damage to coral reefs. Anchoring on a reef can kill corals, and even a single boat grounding can result in severe physical damage to a large area of the reef.

Recreational Misuse

Recreational activities such as diving and snorkelling, when not conducted responsibly, can contribute to the degradation of coral reefs. This includes accidental contact with the reef, such as touching or kicking corals, as well as improper equipment handling. Increased sedimentation from recreational activities can also smother corals and impede their growth.

Coral Harvesting

The collection of coral for the aquarium trade, jewellery, and curios can result in the physical destruction of coral reefs and their habitats. This can involve the removal of coral colonies, the destruction of reef structures, and the reduction of biodiversity.

Storms and Natural Disasters

It is important to address these sources of physical damage to coral reefs through regulation, education, and the implementation of sustainable practices. By reducing physical damage and combining local and global conservation efforts, we can help protect and restore the health and resilience of coral reefs.

Climate change

Coral bleaching occurs when stressed corals expel their zooxanthellae, revealing their white skeleton underneath. Bleached corals become more vulnerable to additional stressors, such as disease and storms. With climate change, the frequency of marine heatwaves is increasing, leaving corals with insufficient time to recover. As a result, coral reefs are rapidly declining, leading to a loss of habitat for thousands of marine species that depend on them.

In addition to warming oceans, the increase in atmospheric carbon dioxide is causing the ocean to become more acidic. This process, known as ocean acidification, reduces the availability of dissolved salts and ions needed by corals to form their calcium carbonate structures. As a result, coral growth slows, and if acidification becomes severe, coral skeletons may even dissolve.

Other impacts of climate change on coral reefs include sea level rise, changes in storm patterns, altered ocean currents, and changes in precipitation. These changes can lead to stronger and more frequent storms, altered connectivity and temperature regimes, and increased runoff of freshwater, sediment, and land-based pollutants. The combined effects of these factors further stress coral reef ecosystems, disrupting their function and the services they provide to people worldwide.

To address the threat of climate change to coral reefs, it is crucial to reduce greenhouse gas emissions and transition to more sustainable practices. This includes shrinking our carbon footprint, reducing the use of lawn and garden chemicals, choosing sustainable seafood, and practising good reef etiquette when in the water.

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