Pollution's Impact: Coral Reefs In Danger

Coral reefs are some of the most biologically diverse ecosystems on Earth, but they are in crisis. Pollution from land, including hot water releases from power plants, pathogens, trash, and from marine activities, such as fuel leaks and oil spills, endangers coral reefs. Poor water quality, caused by sewage discharge, agricultural activities, and industrial chemicals, can lead to harmful algal blooms, which produce toxins detrimental to coral health. Plastic pollution is also a growing problem, with plastic debris physically damaging coral structures and introducing diseases. Climate change, overfishing, and destructive fishing techniques further threaten coral reefs. Addressing these issues requires concerted efforts from governments, industries, and communities to implement better waste management practices, reduce pollution, and protect these vulnerable ecosystems.

Climate change and ocean acidification

Coral reefs are among the most biologically diverse ecosystems on Earth. They are, however, facing significant challenges from human activities, including pollution, overfishing, physical destruction, and climate change. Climate change and ocean acidification have detrimental effects on coral reefs.

Ocean acidification refers to a change in ocean chemistry in response to the uptake of carbon dioxide from the atmosphere. The amount of carbon dioxide in the atmosphere is in equilibrium with that in seawater. Thus, when atmospheric concentrations increase, so do oceanic concentrations. Carbon dioxide entering seawater reacts to form carbonic acid, causing an increase in acidity. Each year, the ocean absorbs about one-quarter of the carbon dioxide emitted from the burning of fossil fuels (oil, coal, and natural gas). Since the Industrial Revolution, ocean acidity has increased by about 30%, a rate that is more than 10 times what has previously occurred over millions of years. Ocean acidity levels are expected to increase by an additional 40% by the end of this century.

Ocean warming and acidification from increasing levels of atmospheric CO2 represent major global threats to coral reefs. They impair coral growth and increase coral mortality, even under high grazing intensity and low nutrients. Ocean acidification and warming will also lower coral reef resilience. For example, reefs already subjected to overfishing are likely to be more vulnerable to increasing CO2 levels.

Ocean acidification is predicted to lead to reduced rates of calcification for most marine calcifying organisms, including corals. By reducing the growth potential and survivorship of corals, ocean warming and acidification are likely to change the competitive hierarchy of corals and macroalgae. Even lower greenhouse gas emission scenarios are likely to drive the elimination of most warm-water coral reefs by 2040-2050.

The impact of climate change on coral reef organisms has ramifications for ecosystems, some of which may be transformative in terms of their effects on primary productivity, food web dynamics, habitat-forming species, disease ecology, and many other aspects.

Overfishing and unsustainable fishing

Coral reefs are among the most biologically diverse and valuable ecosystems on Earth. Overfishing and unsustainable fishing are some of the key local threats to coral reefs. Coral reefs support important commercial, recreational, and subsistence fisheries in the US and its territories. Many coastal and island communities depend on coral reef fisheries for food, income, and cultural benefits. However, overfishing and unsustainable fishing practices can have detrimental effects on coral reefs and the ecosystems they support.

Coral reef fish are a significant food source for over a billion people worldwide. Rapid human population growth, increased demand, and the use of more efficient fishing technologies have led to the depletion of key reef species. Certain types of fishing gear, such as nets, traps, and lines, can inflict serious physical damage to coral reefs. For example, nets can catch young fish before they have a chance to replenish the population. Traps set too close to reefs can damage coral structures, and lost or discarded fishing gear can entangle and kill reef organisms.

Some fish species gather in large numbers at predictable times and locations to mate, making them particularly vulnerable to overfishing. The absence of large fish can lead to a decline in fish populations over time. Additionally, unsustainable fishing practices can physically destroy entire sections of coral reefs. For example, blast fishing can destroy a large area of reef with a single blast.

The impacts of unsustainable fishing on coral reef areas can have ripple effects on both the coral reef ecosystems and the local economies that depend on them. Coral reefs take a long time to recover, and the loss of key reef species can disrupt the entire ecosystem. Therefore, it is crucial to enforce fishing regulations, promote sustainable fishing practices, and protect coral reef habitats to ensure the preservation of these valuable ecosystems.

Furthermore, it is important to address the issue of ghost gear, which refers to lost or abandoned fishing gear. Ghost gear can continue to entangle and harm marine life, including coral reefs, long after it has been discarded. Implementing measures to reduce and retrieve ghost gear can help mitigate its impact on coral reefs and other marine habitats.

Pollution from land-based sources

As human populations expand in coastal areas, human activities that degrade coral reefs become more intertwined with the social, cultural, and economic fabric of regional coastal communities. This expansion also alters the landscape, increasing land-based sources of pollution and threatening coral reef health.

Land-based sources of pollution include coastal development, deforestation, agricultural runoff, oil and chemical spills, and sewage discharge. These sources can impede coral growth and reproduction, disrupt ecological functions, and cause disease and mortality in sensitive species. For example, sewage discharge and stormwater runoff may introduce pathogens into coral reef ecosystems, causing coral disease.

Agricultural practices, such as the overuse of fertilisers and pesticides, can also contribute to land-based pollution. Excess nutrients from fertilisers can lead to increased algae growth, blocking sunlight and consuming oxygen needed by corals for respiration. This can result in an imbalance affecting the entire ecosystem. Pesticides can also interfere with coral reproduction and growth, affecting their symbiotic relationship with algae and resulting in bleaching.

In addition, plastic pollution is a significant threat to coral reefs. Plastic debris, including abandoned fishing nets and gear, can entangle and kill reef organisms, break or damage coral structures, and block sunlight needed for photosynthesis. The presence of plastic waste has also been associated with a 20-fold increase in the incidence of coral disease, possibly due to bacteria transferred from the plastic.

To preserve and restore coral reef ecosystems, it is crucial to address these land-based sources of pollution through improved land-use practices, wastewater management, and policy interventions. This includes reducing nutrient runoff, properly managing plastic waste, and curbing unsustainable fishing and coastal development practices.

Plastic pollution and marine debris

Coral reefs are incredibly diverse ecosystems that are under threat from human activities. Marine debris, in particular, poses a significant risk to the health and survival of coral reefs. Marine debris, which includes plastic pollution, is predominantly caused by land-based sources, with 90% of debris entering aquatic systems from landfills, litter, sewage discharge, and personal care products.

Plastic pollution is a growing problem for our oceans, and coral reefs are especially vulnerable. Plastics can physically damage coral structures, breaking branches and impeding growth. Plastic debris can block the sunlight needed for coral photosynthesis, and larger pieces can entangle and kill reef organisms.

Plastics also introduce pathogens, carrying bacteria that cause coral diseases. Studies have found that reefs with plastic debris were 20 times more likely to be diseased than those without. The presence of plastic increases the risk of infection and promotes the development of diseases, contributing to the degradation of coral reefs.

Fishing gear, such as ropes, long lines, and nets, makes up a significant portion of plastic debris in coral reefs. This abandoned fishing equipment continues to trap and kill marine animals, even after being discarded, in a process known as "ghost fishing." Natural disasters, such as hurricanes and tropical storms, can also contribute to marine debris by pulling large structures and household items into the water.

The impact of plastic pollution on coral reefs underlines the importance of reducing plastic consumption, properly recycling plastics, and preventing plastic waste from entering the environment. These steps are crucial in mitigating the pressure on coral reefs and preserving their delicate ecosystems.

Poor water quality and sewage discharge

Excess nutrients from sewage discharges can lead to the growth of algae that blocks sunlight and consumes the oxygen corals need for respiration. This often results in an imbalance that affects the entire ecosystem. Excess nutrients can also support the growth of microorganisms, like bacteria and fungi, that can be pathogenic to corals.

Agricultural activities are a significant source of water pollution. Pesticides, herbicides, and fertilizers used on farms run off into rivers and eventually end up in the ocean. These chemicals promote harmful algal blooms (HABs), which produce toxins detrimental to coral health. They also cause sedimentation, making the water cloudy and further blocking sunlight from reaching the corals.

Industries along coastlines often dump pollutants straight into the ocean, including heavy metals, oil, and other harmful chemicals. These pollutants can have devastating effects on coral reefs. In coastal areas of Thailand, for example, the major sources of pollution are the concentration and discharge of domestic and industrial wastewater and/or sewage from coastal development.

Frequently asked questions