Water Pollution: A Bleak Future For Corals

Coral reefs are indispensable ecosystems that support a diverse range of marine life and provide significant economic and environmental value. However, they face an array of threats, including water pollution, which jeopardizes their very existence. Water pollution, originating from land-based sources, poses a significant risk to the health and survival of coral reefs. As human populations expand along coastlines, the increased runoff from land-clearing, agriculture, and sewage systems introduces a range of contaminants into the ocean, including sediments, nutrients, and toxins, which have detrimental effects on coral reefs and the marine life that depends on them.

Untreated wastewater

Nutrients

Pathogens

Untreated sewage is a breeding ground for bacteria, viruses, and other pathogens. These microorganisms can cause diseases in corals, making them more susceptible to other environmental stressors. While rare, pathogens from inadequately treated sewage can lead to disease outbreaks in corals, especially when combined with other environmental stressors.

Chemicals

Industrial effluents in untreated wastewater often contain toxic chemicals, heavy metals, and synthetic compounds. These substances can accumulate in the tissues of marine organisms, causing long-term health issues and disrupting their reproductive and growth processes. They can also directly damage coral tissues, reducing growth rates and increasing mortality.

Microplastics

Pharmaceuticals and Personal Care Products

Medicines, hormones, and chemicals from personal care products often end up in untreated wastewater. These substances interfere with the hormonal and reproductive systems of marine organisms, leading to population declines and disruptions in ecosystem dynamics.

Industrial pollution

One of the most pressing issues is plastic pollution, which is a growing problem for our oceans. Coral reefs are especially vulnerable to plastic debris, which can physically damage coral structures, breaking branches and impeding their growth. Plastic can also act as a vector for pathogens, introducing diseases and contributing to widespread coral decline. Studies have found that coral reefs with plastic debris are significantly more likely to be diseased than those without.

In addition to plastic, industrial pollution also includes the discharge of toxic substances such as metals, organic chemicals, and pesticides. These pollutants can have far-reaching consequences for coral reefs. For example, pesticides can affect coral reproduction, growth, and other physiological processes, while herbicides can damage the symbiotic relationship between corals and algae, leading to coral bleaching. Metals such as mercury and lead, as well as organic chemicals like polychlorinated biphenyls (PCBs), oxybenzone, and dioxin, are suspected of affecting coral reproduction, growth rate, feeding, and defensive responses.

The impact of industrial pollution on coral reefs is not limited to chemical toxins. Construction activities, deforestation, and coastal development significantly increase sedimentation rates in coastal waters. This excess sediment clouds the water, blocking the sunlight necessary for coral photosynthesis and survival. As sediment accumulates, it can bury and suffocate corals, hindering their ability to regenerate.

The effects of industrial pollution on coral reefs are complex and far-reaching, threatening the very existence of these vital ecosystems. It is crucial to address these issues through concerted efforts from governments, industries, and communities to ensure the preservation of coral reefs for future generations.

Plastic pollution

A four-year study of 159 reefs in the Pacific Ocean found that reefs in Australia, Thailand, Indonesia, and Myanmar were heavily contaminated with plastic. Plastic clings to coral, particularly branching coral, and where it clings, it damages and kills. The likelihood of disease increases from 4% to 89% when corals come into contact with plastic.

Plastic debris promotes the development of diseases in corals. The risk of disease can be up to 22 times greater on a reef polluted by plastic than on an unpolluted reef. Some of the most common coral diseases, such as skeletal eroding band, white syndromes, and black band, are more prevalent on reefs contaminated by plastics. The more complex and branched the coral, the more likely it is to retain plastic debris and be affected.

Plastic debris has a direct impact on the health of coral tissue. It can cause physical damage, such as abrasions, which can lead to infections. Plastic can also block sunlight from reaching the coral, and it can carry pathogens, including bacteria and other harmful microorganisms, which can increase the risk of infection.

Fishing gear, such as ropes, long lines, and nets, was found to be a significant source of plastic pollution in reefs. This type of debris can entangle and kill corals, sponges, and other invertebrates, and it continues to catch fish even after being discarded, a phenomenon known as "ghost fishing."

Low- and middle-income countries tend to have higher levels of plastic pollution in their oceans due to limited resources for waste management and better fishing gear. However, plastic pollution was also found in marine protected areas, indicating that more widespread action is needed to address this issue.

Land run-off

One of the primary issues with land run-off is sedimentation. When rainwater falls on exposed rocks and soil, it breaks them up and carries the particles downhill into the ocean. This sediment can smother corals, interfering with their ability to feed, grow, and reproduce. The shape of coral colonies makes a difference in their ability to shed sediment; for example, thin branching types are good at shedding sediment, while plate or gramophone-shaped colonies are poor at getting rid of it.

In addition to sedimentation, land run-off also introduces excess nutrients into the water, leading to eutrophication. This includes high levels of nitrogen and phosphorus from agricultural areas and sewage outflows. These excess nutrients cause enhanced algal growth on reefs, which crowds out corals and degrades the ecosystem.

The impact of land run-off on coral reefs is particularly significant in the Caribbean, where approximately 80% of ocean pollution originates from land-based activities. Efforts to reduce sediment run-off, such as implementing drainage control systems and using native vegetation for erosion control, are crucial for mitigating the effects of land-based pollution on coral reefs.

Climate change

The increase in greenhouse gases is also causing ocean acidification. The ocean absorbs carbon dioxide from the atmosphere, which alters seawater chemistry through decreases in pH. This process is called ocean acidification, and it reduces the ability of corals to build their skeletons and form coral reefs. Corals build their skeletons from calcium carbonate, but as the ocean becomes more acidic, the availability of this compound decreases. This makes it harder for corals to build and maintain their skeletons, reducing their structural integrity and making them more vulnerable to destruction by storms.

The warming of the oceans also poses a significant threat to coral reefs. As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Coral bleaching occurs when corals, under heat stress, expel the microscopic algae (zooxanthellae) that live inside their tissues. These algae give the coral its colour, so when they are expelled, the coral appears bleached. The coral is not dead, but it is weakened and more susceptible to starvation and disease. If the algae do not return, the coral will eventually die. While coral reefs can recover from bleaching over time, this requires temperatures to drop and conditions to return to normal. With climate change, the warming of the oceans is expected to continue, making recovery more difficult.

In addition to ocean warming and acidification, climate change is also causing changes in ocean circulation patterns and precipitation. Changes in ocean currents can lead to alterations in connectivity and temperature regimes, resulting in a lack of food for corals and hampering the dispersal of coral larvae. Increased runoff of freshwater, sediment, and land-based pollutants due to changes in precipitation contribute to algal blooms and reduce light penetration, affecting coral reefs.

The combination of these factors associated with climate change is having a devastating impact on coral reefs, threatening the entire ecosystem and the livelihoods of millions of people who depend on them. Urgent global action to reduce greenhouse gas emissions and strengthen key ecosystems that help absorb carbon dioxide is necessary to protect and preserve coral reefs.

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