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Ocean Acidification: Causes and Effects

Updated: May 31, 2023

Colorful corals of the great barrier reef with a lot of small little fish swimming in the backdrop of vast blue sea
The Great Barrier Reef (Source:

Have you heard of The Great Barrier Reef? The largest coral reef chain in the world consists of 3000 individual reef systems and encompasses hundreds of breathtaking tropical islands, which can be seen from space. Due to its beauty and biodiversity, it is considered one of the seven wonders of the natural world. But, the bad news is, the beauty of the Great Barrier Reef might vanish soon.

The Great Barrier Reef and many other reefs in the world’s ocean are facing severe issues that cause their coral distribution to decline and the whole coral structure to weaken, which makes it hard for them to endure climate change threats. One of the major factors in this issue is ocean acidification.

The Problem of Ocean Acidification

Ocean acidification is a phenomenon that occurs when the ocean absorbs an increased amount of CO2 from the atmosphere, resulting in an increase in the ocean's acidity levels.

Research by Lüthi et al. (2008), shows the concentration of CO2 due to human activities such as burning fossil fuels (e.g., car emissions), industrial production, and changing land use (e.g., deforestation) has increased as much as 50% since the industrial revolution. It is higher than anything before for more than 800,000 years. At the same time, about one-quarter of manmade carbon emissions are absorbed into the ocean (Sabine & Feely, 2007).

What Causes Ocean Acidification?

Infographic Illustration  of Ocean Acidification process with icons of chemical bonds
Ocean Acidification Chemical Process (Image credit: NOAA)

Carbon dioxide (CO2) in the atmosphere dissolves into seawater (H2O) and combines to form carbonic acid (H2CO3), it is a weak acid that breaks into hydrogen ions (H+) and bicarbonate ions (HCO3-) (University of Plymouth, n.d.). As more carbon dioxide is absorbed into the ocean, more carbonic acid and hydrogen ions will be created and making ocean water more acidic by decreasing the acidity level (pH).

The ocean pH has decreased by 0.1 pH unit with the current ocean pH level around 8.1, which is basic (or alkaline), since the industrial revolution. This seemingly small shift means the ocean water is already about 28% more acidic than in the pre-industrial era (Borunda, 2019). According to Feely et al. (2009), ocean acidification is expected to lower ocean pH by 0.3 – 0.4 units compared to pre-industrial values by the end of this century if we continue doing business as usual.

Ocean Acidification and Its Effects

4-picture collage of projected image of pteropods in water of carbonate levels in year 2100
Pteropods in water with pH and carbonate levels projected for the year 2100 (Photo by David Liittschwager/National Geographic Stock)

This decrease in ocean pH levels significantly impacts a lot of marine species. Kleypas & Yates (2009) compiled the effects of ocean acidification on the species, especially living organisms in coral reefs. It’s no secret that coral reefs play important roles in increasing and maintaining the biodiversity of the ocean ecosystem, not to mention also the benefits that humans experience from corals. There are also ongoing studies and debates around coral reefs’ role as blue carbon ecosystems (as explained in CVC unit 3).

a. Ocean Acidification Weaken Coral Reefs

vast bed of bleached corals in white color
Coral Bleaching

The coral reef ecosystem is some of the most diverse ecosystems in the world that comprises complex reef systems created by animals called coral polyps (NOAA, 2019). Coral reefs are home to diverse marine species. But, ocean acidification has lead to calcifying organisms (corals and calcifying macroalgae) bleaching and hindering the calcifying process, making coral reefs weaker and easier to dissolve in the ocean water. Kleypas & Yates (2009) found that calcifying organisms will calcify 10-15% less than in the pre-industrial revolution era.

As corals lose their ability to calcify, organisms such as crabs, shrimps, and mussels will lose their home of branching coral (Australian Institute of Marine Science, n.d.). Other calcifying organisms like mollusks (giant clams, squid, pteropods, and gastropods) will produce thinner shells and reduced recruitment rates, while the development of echinoderms organisms (starfish, sea urchins, sand dollars, etc) could be stunted, delayed, or even malformed.

b. Ocean Acidification Impacting Algae and Fish

A clownfish amongst anemone tentacles
Clownfish (Photo by Giorgia Doglioni on Unsplash)

Another research by Tribollet et al. (2009), shows that “endolithic” algae, algae that bore into reef skeletal material, will bore more deeply into reef skeletal material, dissolving nearly 50% more carbonate in the process. Ocean acidification also negatively affects the ability of some fish, like clownfish, to detect predators and locate suitable habitats. And, some species, such as the sur flounder and Atlantic cod, show a decrease in the survival rate of eggs (Falkenberg et al., 2020).

Ocean acidification also lowers the nutritional qualities of seafood, especially in terms of lipids and proteins. For example, It is shown that ocean acidification has led to the reduction of lipids and protein in cultured whelk species (marine sea snails), and some of their lipids are proven to have a health benefit for heart and blood circulation. Also, ocean acidification can modify the abundance and the chemical composition of harmful algal blooms that lead to an increase in shellfish toxicity, which we humans consume.

c. Ocean Acidification and Blue Carbon Ecosystem

multi-color boxes of fresh catch whelk on fishing boat
Boxes of Fresh Catch Whelk (Photo by Catherinelprod Catherine on

Blue carbon is the carbon that is stored by marine and coastal ecosystems such as mangrove forests, seagrass meadows, and seaweed. However, ocean acidification negatively affects the growth and productivity of blue carbon ecosystems to sequester carbon emissions. The increase in ocean acidity reduces the growth rate and survival of seagrass species and the ability of mangroves to store carbon, which further reduces the blue-carbon ecosystem. It is estimated during the 20th century, we had lost 25–50% of blue carbon ecosystems, such as mangroves, seagrass, and salt marshes (Hall-Spencer & Harvey, 2019).

d. Acidification's Impacts on Humans

The decline of the blue carbon ecosystem and the effect of carbon acidification on marine species could also impact humans economically and physically." According to Falkenberg et al. (2020), there are currently 149 million children under the age of five who heavily depend on seafood as a protein source. Unfortunately, a majority of these children are stunted. The decreased quantity and quality of the nutritional composition of seafood can exacerbate this condition. Additionally, a significant decline in coral habitat is projected to have a profound impact on human populations that rely on fisheries, especially communities facing seafood insecurity.

Falkenberg et al. (2020), argue that fewer marine products the fishing community can produce could lead to higher food prices., or Even worse, it can increase unemployment, financial pressures, societal stress, and a decline in the mental health of individual fishermen. Masahiko Fujii, associate professor of environmental sciences at Hokkaido University, said Japan's fisheries and aquaculture industries could face cumulative economic loss of up to ¥2 trillion ($14.4 billion) by 2100 due to ocean acidification.

Solutions to Ocean Acidification

A school of fish above seagrass meadows
Seagrass Meadows (Source: The Ocean Foundation)

The US National Oceanic and Atmospheric Administration (NOAA) has developed an early warning system with buoys that signal more acidified seawater that enables fisheries hatchery managers to schedule production when water quality is right. Ongoing studies examine whether growing seagrasses could be utilized to combat ocean acidification as seagrasses can sequester CO2.

But such solutions only mitigate the negative impact of ocean acidification. The important thing is to tackle the root cause—reducing carbon emissions. As an individual, having a sustainable lifestyle by taking public transport, saving electricity, and supporting clean energy can help reduce carbon emissions and tackle ocean acidification. Educating people about ocean acidification is of utmost importance, considering that it has been relatively recently discovered, yet it is already significantly impacting both our health and the livelihood of marine species, affecting billions of people.

Besides that, helping to protect blue carbon by carbon offsetting could be one of the solutions to mitigate the destruction of the blue carbon ecosystem caused by ocean acidification. Together, we can halt ocean warming and bring back the beauty of coral reefs.

Writer: Fendy Wiedardi Limtara

Editor: Howen Jayawi


Australian Institute of Marine Science. (n.d.). Ocean acidification.

Borunda, A. (2019, August 7). Ocean acidification, explained. National Geographic. Retrieved February 5, 2023, from

Falkenberg, L. J., Bellerby, R. G. J., Connell, S. D., Fleming, L. E., Maycock, B., Russell, B. D., Sullivan, F. J., & Dupont, S. (2020). Ocean Acidification and Human Health. International journal of environmental research and public health, 17(12), 4563.

Feely, R., Doney, S., & Cooley, S. (2009). Ocean acidification: Present conditions and future changes in a High-CO2 world. Oceanography, 22(4), 36-47.

Hall-Spencer, J. M., & Harvey, B. P. (2019). Ocean Acidification Impacts on Coastal Ecosystem Services Due to Habitat Degradation. Emerging Topics in Life Sciences, 3(2), 197-206.

Kleypas, J., & Yates, K. (2009). Coral reefs and ocean acidification. Oceanography, 22(4), 108-117.

Lüthi, D., Le Floch, M., Bereiter, B., Blunier, T., Barnola, J., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K., & Stocker, T. F. (2008). High-resolution carbon dioxide concentration record 650,000–800,000 years before present. Nature, 453(7193), 379-382.

National Oceanic and Atmospheric Administration. (2020, April 1). Ocean acidification. Retrieved February 5, 2023, from

NOAA. (2019, February 1). Coral Reef Ecosystems. Retrieved May 16, 2023, from

Oceana. (n.d.). Major emitters among hardest hit by ocean acidification.

Otake, T. (2022, July 18). Ocean acidification threatens some of Japan’s favorite seafood. The Japan Times. Retrieved February 5, 2023, from

Sabine, C. L., & Feely, R. A. (2007). The oceanic sink for carbon dioxide. NOAA Pacific Marine Environmental Laboratory (PMEL).

Tribollet, A., Godinot, C., Atkinson, M., & Langdon, C. (2009). Effects of elevated pCO2 on dissolution of coral carbonates by microbial euendoliths. Global Biogeochemical Cycles, 23(3), n/a-n/a.

University of Plymouth. (n.d.). What is ocean acidification? Find out how research at Plymouth is tackling this global carbon dioxide problem. Retrieved February 5, 2023, from,bicarbonate%20(HCO3%2D)

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