Greta Jimenez
Coral reefs are some of the most biodiverse ecosystems on Earth, but they are in crisis. According to a 2020 report, 14% of the world's corals were lost between 2009 and 2018, and a 70-90% decrease in live coral on reefs is predicted by 2050. Coral reefs are under stress from climate change, declining water quality, overfishing, pollution, and unsustainable coastal development. Pollution from land-based runoff and marine activities can smother corals, interfere with their ability to feed, grow, and reproduce, and increase the incidence of disease. Warming ocean temperatures caused by climate change also contribute to coral bleaching, where corals expel symbiotic algae and become vulnerable to starvation and death.
| Characteristics | Values |
|---|---|
| Coral dying | Yes |
| Reason | Pollution, climate change, declining water quality, overfishing, unsustainable coastal development, coral bleaching, ocean acidification, rising water temperatures, etc. |
| Percentage of coral lost between 2009 and 2018 | 14% |
| Percentage decrease in live coral on reefs by 2050 | 70-90% |
| Impact of pollution | Coral reefs are affected by leaking fuels, anti-fouling paints, chemicals, sewage, trash, fuel leaks, oil spills, etc. |
| Impact of climate change | Rising sea levels, increased frequency and intensity of storms, altered ocean circulation patterns, coral bleaching, etc. |
| Impact of overfishing | Destructive fishing practices, trawlers, blast fishing, etc. |
| Impact of coastal development | Erosion, sedimentation, dredging, quarrying, etc. |
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What You'll Learn
Climate change and warming ocean temperatures
Coral reefs are some of the most biodiverse ecosystems on Earth. However, they are in crisis due to various global and local issues, with climate change being one of the most significant threats.
Coral reefs are highly sensitive to climate change and rising ocean temperatures. As the oceans absorb heat, their chemistry changes, leading to ocean acidification. This process occurs due to the increased uptake of carbon dioxide from the atmosphere, resulting in the formation of carbonic acid and a subsequent rise in acidity. Since the Industrial Revolution, ocean acidity has increased by approximately 30%, a rate unprecedented in the planet's history. This trend is expected to continue, with acidity levels projected to increase by another 40% by the end of this century.
The increase in ocean acidity reduces the availability of dissolved salts and ions that corals need to form their calcium carbonate structures. As a result, coral and reef growth slows, and some coral skeletons may even dissolve under severe acidification. Additionally, warming ocean temperatures directly stress the corals, causing them to expel symbiotic algae (zooxanthellae) from their tissues, leading to coral bleaching. This bleaching event is the worst ever recorded, affecting reefs from Florida to Australia, and it shows no signs of ending soon.
The combination of long-term climate change and short-term weather phenomena, such as El Niño, contribute to the warming ocean temperatures. Even with urgent reductions in greenhouse gas emissions, it will take decades for global ocean temperatures to stabilize. According to the "Status of Coral Reefs of the World 2020" report, a 70-90% decrease in live coral on reefs is predicted by 2050 without drastic action to limit global warming to 1.5°C.
Other Impacts of Climate Change
In addition to ocean acidification and warming temperatures, climate change has other indirect effects on coral reefs. Rising sea levels, altered ocean circulation patterns, and increased storm frequency and intensity can all damage coral reefs. Furthermore, climate change exacerbates the impacts of other human activities, such as pollution and overfishing, making the reefs more vulnerable to stress and disease.
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Pollution from coastal development
Coral reefs are some of the most biodiverse ecosystems on Earth, but they are in crisis. One of the main causes of coral reef destruction is pollution from coastal development. As human populations expand in coastal areas, the landscape is altered, increasing land-based sources of pollution and threatening coral reef health. Coastal development results in erosion, and the runoff containing excess sediment can block the light that zooxanthellae (microscopic symbiotic algae) need. This causes coral bleaching, where corals expel zooxanthellae and become more sensitive to environmental stressors.
Sedimentation from coastal development is a primary stressor for the existence and recovery of coral species. Sediment deposited onto reefs can smother corals and interfere with their ability to feed, grow, and reproduce. Nutrient-rich fertilizer runoff and sewage effluent can boost algae growth, which starves the water of oxygen, causing eutrophication. This can also lead to increased acidity in coastal waters, exacerbating the effects of ocean acidification, which is caused by the uptake of carbon dioxide from the atmosphere.
Coastal development also increases the risk of toxic substances, including metals, organic chemicals, and pesticides, entering the ocean. These toxins can be found in industrial discharges, sunscreens, urban and agricultural runoff, mining activities, and landfill runoff. Pesticides and herbicides can affect coral reproduction, growth, and other physiological processes, including damaging the symbiotic relationship between coral and algae, resulting in bleaching. Additionally, pathogens from inadequately treated sewage, stormwater, and livestock pen runoff can cause coral disease, especially in stressed corals.
Plastic pollution is another significant issue, with a recent study finding that the incidence of disease in corals increases twentyfold when they come into contact with plastic waste. As coastal development expands, the amount of plastic and other waste polluting the ocean is likely to increase, further endangering coral reefs. Overall, unsustainable coastal development is a major contributor to the decline of coral reefs, and efforts to protect these valuable ecosystems must address this issue.
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Sewage, stormwater, and agricultural runoff
Coral reefs are one of the most biologically diverse ecosystems on Earth. They are under constant stress from climate change, declining water quality, unsustainable coastal development, and pollution. As human populations expand in coastal areas, the landscape is altered, increasing land-based sources of pollution and threatening coral reef health. According to the "Status of Coral Reefs of the World 2020" report, 14% of the world's corals were lost between 2009 and 2018.
Stormwater runoff carries sediment, toxins, nutrients, and pathogens into coral reefs. Sedimentation, caused by coastal development, forestry, and agriculture, is a primary stressor for coral reefs. Sediment deposited on reefs can smother corals, impairing their ability to feed, grow, and reproduce. Toxins, including metals and organic chemicals, found in stormwater runoff can affect coral reproduction, growth, feeding behaviours, and defensive responses.
Agricultural runoff, including pesticides and herbicides, poses a significant threat to coral reefs. Pesticides can impact coral reproduction, growth, and physiological processes. Herbicides can harm symbiotic algae, disrupting their relationship with corals and leading to coral bleaching. Additionally, agricultural practices, such as deforestation, grazing of feral animals, and road building, can alter drainage basins, increasing sedimentation and nutrient runoff into coral reef ecosystems.
To protect coral reefs from the detrimental effects of sewage, stormwater, and agricultural runoff, it is crucial to implement sustainable practices. This includes responsible fertilizer and pesticide use, proper waste management, and the reduction of land-based sources of pollution. By addressing these issues, we can help safeguard the health and resilience of coral reefs, ensuring their survival for future generations.
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Destructive fishing practices
Coral reefs are some of the most biodiverse ecosystems on Earth, but they are in crisis. One of the many threats to coral reefs is destructive fishing practices. Destructive fishing practices can physically destroy entire sections of coral reefs. For example, blast fishing—the use of explosives to kill fish—can destroy 5.9 square meters of reef with a single blast.
Other unsustainable fishing practices can also have a detrimental impact on coral reefs. The use of certain types of fishing gear, such as nets and traps, can inflict serious physical damage on coral reefs and other important marine habitats. Non-selective gears, like nets and traps, often remove more herbivorous fishes, which eat algae and help maintain the ecosystem's balance. In addition, coral reefs are particularly vulnerable to anchors and groundings from boats, which can cause physical damage.
Fishing practices that target coral reefs directly can also be destructive. Coral harvesting for the aquarium trade, jewelry, and curios can lead to over-harvesting of specific species, destruction of reef habitat, and reduced biodiversity. Overfishing can alter food-web structures and cause cascading effects, such as a reduction in the number of grazing fish that keep corals clean of algal overgrowth. This can result in an increase in the susceptibility of coral reefs to disease and invasive species.
The impacts of unsustainable fishing practices on coral reefs can have far-reaching consequences, affecting not only the coral reef ecosystems themselves but also the local economies that depend on them.
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Ocean acidification
Coral reefs are some of the most biodiverse ecosystems on Earth, but they are in crisis. Human activities have put reefs under relentless stress, with climate change, declining water quality, overfishing, pollution, and unsustainable coastal development all contributing to the degradation of coral reefs.
The impact of ocean acidification on coral reefs is twofold. Firstly, it directly affects the ability of corals to build and maintain their skeletons. Corals have skeletons made of aragonite, a form of calcium carbonate. They grow their skeletons by stacking and thickening bundles of aragonite crystals. However, as the ocean becomes more acidic, the absorption of carbon dioxide makes it harder for corals to accrete these skeletons. Laboratory experiments and field studies have shown that corals in more acidic waters have significantly thinner and less dense skeletons, making them more vulnerable to breakage.
Secondly, ocean acidification exacerbates the effects of other stressors on coral reefs. For example, nutrient runoff from land-based activities, such as agriculture and coastal development, can cause eutrophication, leading to oxygen depletion and creating a challenging environment for coral growth. Additionally, pathogens and toxic substances from industrial discharges, sunscreens, and agricultural runoff can increase the incidence of coral diseases. The combination of ocean acidification and these additional stressors can have devastating consequences for coral reefs.
The effects of ocean acidification on coral reefs are already being observed. A recent study found a 14% decrease in coral growth in the Great Barrier Reef since 1990, the most significant decline in the last 400 years. Furthermore, if carbon dioxide concentrations continue to rise, it is predicted that coral reefs will stop growing and begin to erode. This erosion will have far-reaching consequences, as coral reefs provide habitats and nursery areas for numerous marine organisms. The loss of coral reefs would not only impact marine biodiversity but also the livelihoods of coastal communities that depend on them for tourism, fisheries, and coastal protection.
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Frequently asked questions
Coral bleaching occurs when corals are stressed by environmental factors such as pollution, warming ocean temperatures, and natural causes like hurricanes, El Niño, and diseases. They expel the symbiotic algae zooxanthellae from their tissues, which causes them to turn pale or white.
Pollution can directly damage coral reefs through plastic entanglement and smothering. Land-based pollution, including agricultural and sewage runoff, can also increase nutrient levels in the water, promoting excessive algae growth that starves the water of oxygen and smothers corals. Additionally, pollutants such as metals, organic chemicals, and pesticides can affect coral reproduction, growth, and feeding.
Pollution that harms coral reefs originates from various land-based and marine activities. Land-based sources include sedimentation from coastal development, stormwater runoff, forestry, agriculture, and sewage treatment plants. Marine sources include fuel leaks, oil spills, leaking fuels, anti-fouling paints, and chemical discharges.
Coral reefs are extremely biodiverse ecosystems that provide numerous benefits to both the environment and humans. They offer protection to shorelines from hurricanes and support fisheries that approximately 500 million people depend on for their livelihoods. Additionally, coral reefs are a source of new drugs with potential applications in cancer treatment. The loss of coral reefs would have significant ecological, economic, and social consequences.
