In laboratory experiments, this pteropod shell dissolved over the course of 45 days in seawater adjusted to an ocean chemistry projected for the year 2100. Credit: NOAA Environmental Visualization Laboratory 

From oysters to coral reefs: why ocean acidification matters

Next Generation Science Standards

  • HS-ESS3-6. Use a computational representation to illustrate the relationships among Earth systems and how those relationships are being modified due to human activity.
  • HS-ESS3-5: Analyze geoscience data and the results from global climate models to make an evidence-based forecast of the current rate of global or regional climate change and associated future impacts on Earth systems.
  • HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.


Maybe a very quick summary of this story from CA:

Humboldt Bay has been fertile ground for oyster farmers for decades. The multimillion-dollar industry has sustained the small communities that dot the Northern California coastline. However, recent harvests have come up short and have put many small, family-owned businesses at risk. Fresh oysters are getting harder and harder to come by and it’s all due to one factor: Ocean Acidification. As more carbon has entered the atmosphere, the oceans have become more acidic, hurting not only oyster farmers but marine food webs across the world.

Climate change’s evil twin

Since the beginning of the Industrial Revolution around in the mid-18th century, carbon dioxide (CO2) in our atmosphere began to increase dramatically, from around 280 parts per million to above 410 parts per million today, due to the burning of fossil fuels (i.e. coal, oil, and natural gas) to power nearly everything in our lives, from our cars to our electronics. Combustion, the chemical process of burning fuels, combines oxygen with carbon in the air to create CO2. Carbon dioxide is a greenhouse gas (GHG), which “traps” some of the sun’s heat in our atmosphere, allowing us to live in a warm, habitable planet, and not a freezing wasteland. However, the human-caused increase of these gasses has led to higher global temperatures and caused changes in our climate, like more frequent and intense storms and wildfires, etc. 

The CO2 concentration in the atmosphere from 1958-2019. Photo Credit: NOAA

But there is another problem with too much atmospheric CO2 –  the ocean absorbs 30% of CO2 from the atmosphere. When CO2 is dissolved in the ocean, it forms carbonic acid (H2CO3) and increases the acidity of the water. This is a naturally occurring process called carbon sequestration, which also helps keep our planet at a livable temperature. Oceanic phytoplankton and algae also absorb CO2, which they use to photosynthesize, breathing it in and releasing oxygen out. However, with so much extra carbon dioxide in the atmosphere, the ocean is starting to become too acidic. 

Measuring the potential hydrogen (pH) content of water tells us how acidic or basic water is. The pH scale is from 0 to 14, with 7 is the neutral point (pure water). The closer a solution’s pH is to 0, the more acidic it is; the closer a solution’s pH is to 14, the more basic it is. Ocean water is still slightly alkaline, or basic. But since the beginning of the Industrial Revolution, the ocean pH levels have dropped from 8.2 to 8.1. This seems small, but it’s actually equal to a 30% increase in acidity. By the end of this century, if we continue to burn fossil fuels at our current rate, ocean pH could drop to under 7.8 pH, more than 150% more acidic than ever previously observed in human existence. In fact, ocean water hasn’t seen a pH level that low in more than 20 million years. 

pH is measuring in a base 10 scale – meaning that a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4.  Credit: Ocean Atlas 2017, Petra Böckmann/Heinrich Böll Foundation

Why does this matter?

The ocean is vital to all life on Earth, from the marine creatures to humans all around the planet who rely on the ocean for their livelihood. Even though most of us don’t spend the majority of our time in the ocean, our actions on the land affect everything the sea, like its temperature, acidity, and the well-being of its plants and animals.

Even small shifts in pH can make a big difference in the health of marine critters. Calcifying organisms (e.g. snails, clams, crabs, lobsters, and oysters, various ocean plants, and pteropods) have shells or skeletons that are made out of calcium carbonate. Coral polyps, animals that live in large colonies, are also made out of calcium carbonate and are the building blocks of coral reefs. More acidic salt water makes it more difficult for these calcifying organisms to build and maintain their shells, making it harder for them to survive. 

Changes in ocean chemistry can even hurt non-calcifying animals. The Seattle Times reported that pollock, a valuable fish species on the U.S. West Coast, have a harder time finding other predators in more acidic water. The risks to these animals threaten entire global food webs, and humans are part of these food webs.

Many jobs and economies are tied to fish and shellfish. The global mollusk aquaculture industry is worth more than $29 billion a year, and ocean acidification is a huge threat to this market. It is estimated that by 2100, losses due to declines in mollusk production from ocean acidification may be around USD 130 billion. Pacific Northwest oyster hatcheries have already been impacted, as they have seen declines in larval settlement and survival rates.

Coral reefs are very important to everyone, not just those who live near these ecosystems. They are biodiversity hotspots, provide coastal protection, are important fisheries habitats, a source of life-saving medicine, and generate huge tourism and recreation value. 

And it’s not just about money. More than 3 billion people rely on food from the ocean as their primary source of protein. Without seafood to eat, many of these people will have to move where there is food available, and they will lose that healthy, local protein source.

Educators in the Chesapeake Bay learning about the Eastern Oyster. Credit: NOAA’S National Ocean Service

What can we do?

Despite this seemingly overwhelming challenge, many people around the world researching, educating and creating policies to help people mitigate and adapt to these changes. For instance, NOAA’s Ocean Acidification Program builds relationships between scientists, resource managers, policymakers, and the public to better research and monitor the effects of changing ocean chemistry on ecosystems, like fisheries and coral reefs. Supporting programs like this help assure these important collaborations continue.

Educational tools like NOAA Data in the Classroom’s ocean acidification module teaches students about ocean and coastal acidification through interactive web maps, apps, and videos. 

Youth climate activists in front of the U.S. Capitol protesting for climate action (Credit: Maggie Allen)


Shellfish farmers, whose livelihoods depend on healthy marine ecosystems, are preparing for these shifts in ocean chemistry. For example, Bill Mook of Mook Sea Farm, located in coastal Maine, grows tiny oysters in tanks for his business and other oyster farmers. Mook and researchers from the University of New Hampshire have built and started using a “black box”, which measures the amount of carbonate in seawater pumped into his hatchery. This technology tells him how his oysters grow in different pH conditions, which may help these shellfish adapt to changing waters.

But at the end of the day, it all comes back to taking climate action. Our energy system has powered our economy for a couple of centuries; now we need to move away from fossil fuels as an energy source and shift towards renewable power, like wave, solar and geothermal. Governments and industries must implement these cleaner systems on a large scale. It goes beyond just putting your own solar panels on your roof, but also working for change policy at the city, state, national, and even international level. The more people who take action and talk to our energy companies and governments, the more likely it is they will respond and start making this shift. If we act now, we can continue to enjoy healthy coral reefs, eat delicious oysters, and assure the survival of our One Ocean for generations to come.

Learn more:

KQED has a great video that explains how pteropods, small free-floating marine snails, are struggling to build their shells in an increasingly acidic ocean and the effects on marine food webs.

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