How Is Coral Affected By Ocean Acidification

 How Is Coral Affected By Ocean Acidification


How Is Coral Affected By Ocean Acidification: Coral reefs are among the most diverse and productive ecosystems on our planet, providing habitat for a multitude of marine species and offering invaluable services to humans, including fisheries, tourism, and coastal protection. However, these magnificent underwater ecosystems face a grave threat: ocean acidification.

Ocean acidification is a consequence of the increased concentration of carbon dioxide (CO2) in our atmosphere due to human activities, primarily the burning of fossil fuels and deforestation. As a result, the world’s oceans absorb significant amounts of CO2, causing a chemical shift in seawater.  

Coral reefs, which are built by tiny marine animals called coral polyps, are highly sensitive to changes in their environment, including shifts in pH. Ocean acidification poses a severe threat to these delicate ecosystems. As seawater becomes more acidic, corals struggle to build their calcium carbonate skeletons, which are essential for their growth and structural integrity.  

In this exploration of how coral is affected by ocean acidification, we will delve into the mechanisms behind this phenomenon, its consequences for coral reefs, and potential solutions to mitigate its impacts. Understanding the intricate relationship between coral and ocean acidification is vital for the conservation and preservation of these extraordinary ecosystems in an ever-changing world.

How Is Coral Affected By Ocean Acidification

What type of corals are harmed by ocean acidification?

Alongside threatened tropical coral reefs, cold-water corals are some of the most vulnerable species when it comes to anthropogenic carbon dioxide emissions.

Ocean acidification poses a significant threat to various types of corals, but its impacts can vary depending on the specific species and their adaptations to changing environmental conditions.

  • Stony Corals (Scleractinia): Stony corals, which are responsible for building the massive reef structures we commonly associate with coral reefs, are particularly vulnerable to ocean acidification. These corals rely on calcium carbonate to form their skeletons, and as seawater becomes more acidic, it hampers their ability to calcify effectively. This weakened calcification makes them more susceptible to physical damage and inhibits their growth.
  • Soft Corals: Soft corals, including various types of sea fans and sea whips, tend to be more resilient to ocean acidification compared to stony corals. They lack the hard calcium carbonate skeleton and have a different method of support, which makes them less directly affected by declining pH levels. However, the overall health of the ecosystem, which soft corals are a part of, can still be impacted indirectly due to the interconnectedness of marine life.
  • Deep-Sea Corals: Corals found in deep-sea environments are also at risk. These corals often live in areas with naturally low pH levels, but the rapid increase in ocean acidification can still negatively affect their ability to calcify and grow.

It’s crucial to note that while some coral species may exhibit more resilience to ocean acidification, the overall health of coral reef ecosystems depends on the collective well-being of various coral species, as well as the diverse array of marine life they support. The conservation and protection of all coral types are essential to preserving the biodiversity and ecological services that coral reefs provide.

Does ocean acidification cause coral reefs to be dead?

Under acidified conditions, the dead coral skeleton becomes more porous, weakens, and eventually crumbles. The live coral can still grow under these corrosive conditions, but the reef structure is less complex and less capable of supporting biodiversity.

The primary way in which ocean acidification affects coral reefs is by hindering the ability of coral polyps to build and maintain their calcium carbonate skeletons. As seawater becomes more acidic due to increased carbon dioxide (CO2) levels, the process of calcification becomes less efficient for corals. This weakened calcification can result in slower coral growth and the erosion of existing reef structures.

While ocean acidification is a serious threat, coral reefs can recover and adapt if they are not exposed to multiple stressors simultaneously. However, when combined with other stressors such as rising sea temperatures, pollution, overfishing, and physical damage from human activities, the cumulative impacts can become severe and lead to reef degradation and, in some cases, mortality.

Efforts to mitigate ocean acidification and reduce its root cause, which is the excessive release of CO2 into the atmosphere, are crucial to preserving coral reefs. Additionally, strategies like marine protected areas, sustainable fishing practices, and coral restoration initiatives can enhance the resilience of coral ecosystems and help them withstand multiple stressors. 

How does CO2 affect coral reefs?

As oceans absorb carbon dioxide (CO2), they become more acidic. This affects the ability of reef-building corals to grow their skeletons and form the foundation for coral reefs. Weaker skeletons also make corals more vulnerable to disease and destruction by storms.

Carbon dioxide (CO2) affects coral reefs primarily through a process known as ocean acidification, which has a range of detrimental impacts on these vital marine ecosystems. Here’s how CO2 affects coral reefs:

  • Ocean Acidification: As atmospheric CO2 levels rise due to human activities like burning fossil fuels, a significant portion of this CO2 is absorbed by the world’s oceans. When CO2 dissolves in seawater, it forms carbonic acid, which lowers the pH of the ocean. This increased acidity makes it more challenging for marine organisms, including corals, to build and maintain their calcium carbonate skeletons and structures. This weakened calcification hampers coral growth and can lead to the erosion of existing reef structures.
  • Coral Bleaching: Elevated CO2 levels also contribute to rising sea temperatures, which can trigger coral bleaching events. When water temperatures become too high, the symbiotic algae called zooxanthellae living within coral tissues are expelled. Without these algae, corals lose their vibrant colors and primary food source, making them more susceptible to stress and disease.
  • Weakened Resilience: Ocean acidification reduces the overall health and resilience of coral reefs, making them more susceptible to other stressors, such as pollution, overfishing, and physical damage. Weakened corals are less able to recover from disturbances and are more likely to succumb to environmental pressures.

The increase in CO2 levels, primarily driven by human activities, exacerbates ocean acidification and contributes to a cascade of negative effects on coral reefs, including weakened calcification, coral bleaching, and reduced resilience. Addressing CO2 emissions and adopting sustainable practices is crucial for safeguarding the health and future of these vital marine ecosystems.

How is coral affected by ocean pollution?

When sediment and other pollutants enter the water, they smother coral reefs, speed the growth of damaging algae, and lower water quality. Pollution can also make corals more susceptible to disease, impede coral growth and reproduction, and cause changes in food structures on the reef.

Coral reefs, often referred to as the “rainforests of the sea,” are intricate ecosystems that provide habitat for a vast array of marine life. Unfortunately, they are highly vulnerable to the detrimental effects of ocean pollution. Here’s how coral is affected by ocean pollution:

  • Chemical Contaminants: Pollutants such as oil, heavy metals, pesticides, and sewage runoff can enter the ocean and settle on coral reefs. These chemicals can disrupt the delicate balance of the reef ecosystem and harm coral health. For example, heavy metals can interfere with coral reproduction, and certain pesticides can be toxic to coral polyps.
  • Nutrient Runoff: Agricultural runoff and untreated sewage discharge introduce excess nutrients like nitrogen and phosphorus into coastal waters. This nutrient enrichment can lead to a process called eutrophication, which promotes the rapid growth of algae. Algal blooms can smother coral reefs, block sunlight, and outcompete corals for space and resources.
  • Plastics and Debris: Plastic pollution is a growing threat to coral reefs. Corals can become entangled in discarded fishing nets and other debris, causing physical damage. Additionally, small plastic particles can be ingested by coral and other marine organisms, potentially harming their digestive systems.
  • Ocean Acidification: While ocean pollution is often associated with direct chemical contamination, it can indirectly contribute to ocean acidification when pollutants, such as excess CO2 from human activities, are absorbed by the ocean. As mentioned previously, ocean acidification can weaken coral skeletons and hamper their growth.

Efforts to protect coral reefs from pollution include improving wastewater treatment, implementing sustainable agricultural practices, reducing plastic waste, and promoting responsible fishing and shipping practices. Addressing ocean pollution is vital for preserving these valuable and fragile ecosystems.

How does ocean acidification cause coral bleaching?

Ocean acidification does not cause bleaching, but instead causes the dissolution of the calcium structure that makes up the coral.

Ocean acidification is a critical threat to coral reefs, and it plays a significant role in causing coral bleaching. Coral reefs are made up of colonies of tiny animals called coral polyps, which have a mutualistic relationship with photosynthetic algae called zooxanthellae. These algae provide the coral with essential nutrients and give them their vibrant colors. However, when ocean acidification occurs, it disrupts this delicate balance.

Ocean acidification is primarily driven by the absorption of excess carbon dioxide (CO2) from the atmosphere into seawater. This leads to a decrease in the pH of the ocean, making it more acidic. As the ocean becomes more acidic, it becomes increasingly difficult for coral polyps to build their calcium carbonate skeletons, which form the structural foundation of coral reefs. The acidic conditions hinder the process of calcification, making the corals weaker and more vulnerable.

Elevated ocean acidity can stress coral polyps, causing them to expel their symbiotic zooxanthellae. This expulsion is a defense mechanism employed by the corals to survive in the changing environment, but it comes at a cost. Without the zooxanthellae, the corals lose their main source of nutrients and their vibrant colors, resulting in the phenomenon known as coral bleaching.

Ocean acidification compromises the ability of coral polyps to build and maintain their calcium carbonate skeletons, while also stressing them and causing the expulsion of vital zooxanthellae. These combined effects weaken coral reefs and make them more susceptible to bleaching events, which, if prolonged, can lead to the decline and death of these vital marine ecosystems.

Is ocean acidification the main cause of coral bleaching?

Greenhouse gas emissions are the main cause of ocean acidification and the increases in sea temperature that cause coral bleaching. Any efforts to reduce emissions will bring benefits both on land and at sea. However, global greenhouse gas emissions have risen steadily in recent years.

Ocean acidification is a significant factor contributing to coral bleaching, but it is not the sole cause. Coral bleaching occurs when corals expel the symbiotic algae (zooxanthellae) living within their tissues due to stress. While rising ocean acidity, primarily driven by increased atmospheric carbon dioxide (CO2) levels, plays a role in this stress, it is just one piece of the puzzle.

The primary driver of coral bleaching is elevated sea temperatures. When the ocean water becomes too warm, corals expel their zooxanthellae, leading to the loss of their vibrant colors and the eventual death of the coral if stress persists. This phenomenon is exacerbated by climate change, which leads to more frequent and severe marine heatwaves.

Ocean acidification compounds the problem by weakening coral structures. As the oceans absorb excess CO2, they become more acidic, hindering coral growth and making it harder for them to recover from bleaching events.

Ocean acidification contributes to coral bleaching by weakening corals and reducing their ability to cope with stress. However, the primary driver remains elevated sea temperatures, highlighting the urgent need for global action to mitigate climate change and reduce its impact on coral reefs.

Does ocean acidification weaken coral skeletons?

The new research, led by National Science Foundation (NSF)-funded scientists at the Woods Hole Oceanographic Institution (WHOI), shows that ocean acidification impedes the thickening process — decreasing the skeletons’ density and leaving them more vulnerable to breaking.

Coral skeletons are primarily composed of calcium carbonate, and their formation relies on a delicate balance between carbonate ions and other chemical components in the surrounding water. When the ocean becomes more acidic due to elevated CO2 levels, it reduces the availability of carbonate ions, making it more challenging for corals to build and maintain their skeletons.

As a result, corals under prolonged exposure to acidic conditions are often found to have thinner, more fragile skeletons. Weakened skeletons not only threaten the corals’ structural integrity but also make them more susceptible to physical damage from storms and wave action. Additionally, this can hinder their ability to recover from bleaching events and other stressors, ultimately endangering the entire coral ecosystem.

Ocean acidification is a critical factor contributing to the decline of coral reefs worldwide, as it weakens coral skeletons, making them more vulnerable to various threats and jeopardizing the rich biodiversity that relies on these precious marine habitats. Addressing this issue is imperative to safeguard the future of these vital ecosystems.

How does ocean acidification affect coral reefs Google Scholar?

Our results suggest that ocean acidification alone would lead to declines in Porites coral skeletal density over the 21st century. Such declines in skeletal density could increase the susceptibility of coral reef ecosystems to bioerosion, dissolution, and storm damage (61–63).

This phenomenon results from the absorption of excess carbon dioxide (CO2) from the atmosphere by the oceans, leading to a decrease in seawater pH. Here are some key findings from scientific studies on the subject:

  • Coral Calcification: Research on coral reefs published on Google Scholar consistently highlights how ocean acidification reduces coral calcification rates. As the water becomes more acidic, the availability of carbonate ions decreases, making it harder for corals to build and maintain their calcium carbonate skeletons. This weakening of the skeletons affects the overall health and resilience of coral colonies.
  • Coral Bleaching: Studies show that ocean acidification can exacerbate coral bleaching events, which are primarily triggered by elevated sea temperatures. When corals are stressed by both warmer waters and increased acidity, their ability to recover from bleaching is compromised.
  • Ecosystem Impacts: Ocean acidification not only affects corals but also has broader ecosystem-level consequences. Research on Google Scholar discusses how changes in coral health can disrupt the intricate food web and biodiversity of coral reef ecosystems.
  • Management and Mitigation: Scientists are actively researching management and mitigation strategies to combat the effects of ocean acidification on coral reefs. This includes efforts to reduce CO2 emissions, enhance coral resilience, and restore damaged reefs.
How Is Coral Affected By Ocean Acidification


The threat of ocean acidification to coral reefs is both imminent and alarming. The evidence is clear: as carbon dioxide levels continue to rise due to human activities, the world’s oceans are becoming more acidic, severely impacting coral ecosystems. The consequences of this phenomenon are multifaceted and profound.

Coral reefs, already facing pressures from climate change, pollution, overfishing, and habitat destruction, are now dealing with the added stress of reduced pH levels in seawater. The inability of corals to build and maintain their calcium carbonate skeletons not only weakens the structural integrity of the reefs but also impairs their ability to provide essential habitat for countless marine life.

The ripple effects of coral decline are felt throughout the entire marine ecosystem, affecting the livelihoods of millions of people who rely on fisheries and tourism associated with healthy reefs. This crisis demands immediate attention and concerted global efforts to mitigate the causes of ocean acidification, primarily by reducing carbon emissions and adopting sustainable practices.

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