Coral Bleaching and Ocean Acidification

Topics: Ocean

Coral reefs are a massive ecosystem that is a key part of the ocean habitat. They house tons of biodiversity containing many unique types of fish and plants. These habitats are the only home of many species that inhabit them, and thus they are a key source of biodiversity in the oceans. These ecosystems, like many others around the world, have been experiencing radical change as a result of climate change. In this paper, the way that climate change is affecting the ocean and the impacts that this will have on coral reef ecosystems as well as the potential economic impacts of this will be discussed.

An interesting question that comes to mind when looking at ocean acidification is how it is a result of climate change. The mechanism that converts the excess CO2 into an acidified ocean is a complicated one, and this is compounded by the increasing global temperatures. In water, as temperature increases the amount of water that forms hydronium ions increases, leading to a decrease in the pH of the water and therefore an increase in acidity (Hoegh-Guldberg et.

al, 2007). The other mechanism is a direct result of the increase in the concentration of CO2 in the atmosphere from the burning of fossil fuels. This results in the following reaction mechanism to occur:


This mechanism creates H+ to form increasing the acidity of the water further (Hoegh-Guldberg et. al, 2007).

It is important to understand the effects that this acidification has on species before further delving into where the effects are seen the most strongly.

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Studies have shown that species such as phytoplankton and mollusks have been able to adapt to these changes in acidity during long-term experiments (Gattuso et al., 2014). While this may seem like a positive sign, there is some important historical context that needed to be provided along with this data point: mass extinctions in Earth’s history have been linked to acidifications of the ocean happening at a much slower rate than we are experiencing today, hinting that the evolutionary rates of many species alive today may not be able to adapt quickly enough to the new conditions (Gattuso et al, 2014). This is very important to keep in mind when discussing the impact of this acidification on coral reefs later on.

One of the major factors that drive the change in the acidification is the H+ ion that results from the previous reaction interacting with Calcium Carbonate, CaCO3. This interaction creates carbonate (CO32-) ions, which when combined with the H+ ion create bicarbonate. Concentrations of carbonate are often used in discussions about where acidity is at its highest. Since the shells of many ocean creatures dissolve in the increasingly acidic ocean, the areas with the highest carbonate concentration tell us where acidity is highest (Orr et al, 2005). For evidence as to what types of regions are most prone to experiencing radical changes in their climate as a result of acidity we turn to the 2015 paper by Ekstrom et al. titled “Vulnerability and adaptation of US shellfisheries to ocean acidification.” This paper discusses the regions of the US that are most prone to suffering from acidification from the perspective of shellfisheries, which is in line with the earlier statements of carbonate being an indication of regions that are affected. The article states that the regions most likely to be affected are the US east coast and the Gulf coast, but for different reasons. For the east coast, this is because of the high levels of sensitive creatures that inhabit the region, and for the gulf coast, it is more vulnerable as a result of low adaptive capacity resulting from low effort to combat climate change. To summarize the results, regions most vulnerable to the effects of ocean acidification are areas where it is a highly sensitive ecosystem or a region where little effort has been made to combat the effects of climate change leaving species unable to adapt (Ekstrom et al, 2015). Looking at the points that have been raised related to climate change so far, a link between the climate impacts and coral reefs can be drawn. Coral reefs are primarily made of calcium carbonate, meaning that acidification has a very strong effect in these sorts of regions. To top this off, coral reefs are also highly sensitive ecosystems, further increasing their vulnerability.

Coral bleaching has been an ongoing issue since it was first recorded in 1984. It can be described as the relationship between algae-like protozoa called zooxanthellae and the coral itself and what happens when these zooxanthellae are killed. Zooxanthellae give the coral its nutrients by producing oxygen and ridding the coral of waste through photosynthesis. When bleaching occurs the zooxanthellae are killed and the coral no longer receives these nutrients, therefore, starving the coral and eventually can lead to death. This process is very harmful to oceans and the communities within.

One of the biggest issues caused by the bleaching of coral reefs is what it will do to the species that depend on them. Coral reefs are home to almost one-fourth of species. When bleaching occurs, their homes are lost. Not only are coral reefs a home but also a source of food for many species as well. As coral reefs are killed off, the ocean loses speciation and much of its resources needed to support those ecosystems. Much of the ocean relies on coral reefs and the support they give to a wide variety of organisms within them.

The question to be asked is what is triggering these bleachings throughout the ocean. The main stressors have been defined as increased and decreased temperatures, solar radiation, reduced salinity, and bacterial infections (Glynn P. W.). The greatest trigger in the last couple of years is elevated temperatures caused by CO2 being released and global warming occurring. Therefore, a high majority of bleaching is caused by man and their impact on the environment.

In addition to the organisms that depend on the coral reefs to survive, many economies are built around the tourism industry that is made possible by the coral reefs and the pristine waters that have been associated with them. The coral reef tourism sector itself contributes $36 billion to the travel industry annually, and more specifically 70 countries have reefs that generate over 1 million dollars per square kilometer to the economy (Spalding et. al, 2017). Needless to say, the potential economic impacts of coral bleaching and ocean acidification are staggering, the resulting decline in tourism would heavily impact countless countries’ economies that are centered around tourism and it would have ripple effects throughout the economy. However, the impacts of ocean acidification expand far beyond the tourism industry. For example fishing industries that revolve around sea creatures such as oysters and clams can also be negatively impacted. For example, in the Pacific Northwest of the United States alone, the oyster industry is worth $272 million and accounts for over 3,000 jobs (Orr et al, 2005). Furthermore, shellfish industries in the Gulf of Mexico and the east coast of the United States can also be negatively impacted by ocean acidification which would result in fewer jobs in the industry and the region.

It’s easy to think that since ocean acidification has no direct danger to humans that it’s a problem that can be swept under the rug. This is simply not true. Not only does ocean acidification threaten countless ocean ecosystems, but it has the potential to devastate economies that rely on the ocean and its ecosystem every from tourism to dining.

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Coral Bleaching and Ocean Acidification. (2022, Apr 24). Retrieved from

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