Pollution's Impact: Coral Reefs In Danger

Coral reefs are in decline due to a variety of factors, including pollution. Pollution from land-based sources is a primary cause of coral reef degradation worldwide. As human populations expand in coastal areas, development alters the landscape, increasing runoff from land. This runoff often carries large quantities of sediment, high levels of nutrients from agricultural areas and sewage outflows, and pollutants such as petroleum products and pesticides. These land-based sources of pollution threaten coral reef health and survival.

Nutrient pollution

Coral reefs have evolved to thrive in nutrient-limited environments, and an excess of nutrients can have detrimental effects. While some coral species may exhibit slightly increased growth rates with a slight rise in nutrients, excessive nutrient levels can fuel the competition between endosymbionts and the coral host, reducing growth rates in many coral species. Additionally, elevated nutrient concentrations can increase bioerosion rates, sediment dissolution, and the growth of fleshy macroalgal species, which compete directly with corals for space and resources.

The impact of nutrient pollution on coral reefs is not limited to direct physiological effects on coral growth and physiology. Nutrients can also indirectly affect reefs by altering the pH environment. Photosynthesis and respiration, driven by nutrient availability, have opposing effects on pH, increasing and decreasing it, respectively. This altered pH environment can further impact coral calcification and dissolution rates, with decreased pH enhancing dissolution and impairing the formation of coral skeletons.

The negative consequences of nutrient pollution on coral reefs are evident in studies conducted in various regions. For example, in the Caribbean, increased nitrate levels have been linked to decreased calcification in certain coral species. Similarly, in the Pacific, elevated nutrient concentrations have been associated with a shift from net accretion to net erosion in coral reefs, indicating that nutrient pollution could make reefs more vulnerable to the impacts of ocean acidification.

Addressing nutrient pollution is critical for the long-term health and survival of coral reefs. Implementing measures such as improving wastewater treatment infrastructure, enforcing stricter regulations on wastewater discharges, and adopting sustainable agricultural practices can help mitigate the impacts of nutrient pollution on these invaluable ecosystems.

Sedimentation

Sediment overload has several direct impacts on corals. Firstly, it can cause coral death through smothering. Secondly, corals must expend extra energy on cleaning, leaving less energy for growth, predation, and other vital activities. Thirdly, sediments can cause physical damage to corals through abrasion.

The impact of sedimentation on coral reefs is influenced by various factors, including the concentration, duration, and frequency of exposure, as well as geographic location, sediment type, and coral taxonomy. Understanding these factors is crucial for developing effective conservation and management strategies to protect coral reefs from the detrimental effects of sedimentation.

Toxic substances

Coral reefs are in decline, and toxic substances are a major contributing factor. Metals, organic chemicals, and pesticides are among the toxic substances that have been observed to affect coral reproduction, growth, and defensive responses. These toxins are present in industrial discharges, sunscreens, urban and agricultural runoff, mining activities, and landfill leakage.

Metals such as mercury and lead, and organic chemicals such as polychlorinated biphenyls (PCBs), oxybenzone, and dioxin, are suspected of affecting coral reproduction and growth rates. They also impact feeding and defensive responses. For example, herbicides can affect the symbiotic algae that live within coral tissues and provide them with colour. This disruption can result in coral bleaching, where stressed corals expel their algae partners, causing them to lose their coloration.

Pesticides are another significant toxic threat to coral reefs. They interfere with coral reproduction and growth and can cause coral bleaching. Pesticides can be found in industrial discharges, agricultural runoff, and even personal care products like sunscreens.

Trash and microplastics also fall under toxic substances and pose a significant threat to coral reefs. Plastic waste can physically damage coral structures, breaking branches and impeding growth. Additionally, plastics can act as a vector for pathogens, introducing diseases and contributing to widespread coral decline. Studies have found that coral reefs with plastic debris are 20 times more likely to be diseased than those without.

Untreated or poorly treated wastewater (sewage) is another source of toxic substances that harm coral reefs. Sewage brings high levels of nitrogen and phosphorus, which promote excessive algal growth that smothers coral reefs, blocks sunlight, and depletes oxygen levels. Sewage also introduces bacteria, viruses, and other pathogens that can cause diseases in corals.

In conclusion, toxic substances from various human activities are having detrimental effects on coral reefs. These toxins disrupt coral reproduction, growth, and defensive mechanisms, ultimately contributing to the decline of these invaluable ecosystems.

Marine debris

A survey of 159 coral reefs in the Asia-Pacific region found that, in waters where there were high amounts of plastic, the coral was not healthy. The presence of plastic significantly increased the chance of corals getting sick. The likelihood of a disease outbreak increased from 4% to 89% when corals came into contact with plastic. This is because plastic promotes the growth of harmful pathogens and transports them into coral reefs. Senior author Drew Harvell at Cornell University explained that "plastics abrade corals, creating new openings. They basically tear open the skin of the coral and that can allow an infection from anywhere to start".

In addition, structurally complex corals, such as staghorn coral and other types of branching coral, are eight times more likely to trap plastics within their structures. These types of coral are important nursery habitats as their elaborate structures provide lots of hiding places for juvenile fish.

Another study found that corals were not ingesting plastic by mistake but were actively seeking it out as a snack. There is something dangerously tasty about the chemical compounds in plastic, a development that researchers have warned needs to be better understood to prevent further contamination and disease.

In the Asia-Pacific region alone, there are around 11.1 billion plastic items entangled on coral reefs, and this is expected to jump by 40% by 2025.

Climate change

The average temperature of tropical oceans has increased by 0.1˚ C over the past century. This, combined with natural temperature fluctuations, has resulted in extensive coral bleaching around the globe, affecting thousands of square miles of reefs. During the 1997-1998 El Niño, widespread and severe coral reef bleaching occurred in the Indo-Pacific region and the Caribbean, killing 16% of the world's coral reefs in just 12 months.

In addition to warming seas, the oceans are also experiencing increasing levels of acidification due to rising carbon dioxide (CO2) concentrations. The oceans absorb approximately one-quarter of the CO2 emitted from the burning of fossil fuels, and since the Industrial Revolution, ocean acidity has increased by about 30%. This rise in acidity reduces the availability of dissolved salts and ions that corals need to form their calcium carbonate skeletons. As a result, coral and reef growth slows, and some species are affected more than others. If acidification becomes severe, coral skeletons may even dissolve.

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