Ocean Acidification

Ocean Acidification

The increasing amount of carbon dioxide dissolved in oceans is leading to more acidic seawater that is harmful to many kinds of marine life. Sometimes called climate change’s “evil twin,” ocean acidification poses a critical threat to shell building organisms: they make thinner shells and the shells of some species are actually dissolving.

Pteropod: inset is dissolving shell

Some animals that use calcium carbonate to build shells and skeletons face challenges. Pteropods, free-swimming sea snails called sea butterflies, are often the primary zooplankton at the base the food web in arctic and subarctic waters. These animals may be unable to maintain shells in waters with less available calcium carbonate. Scientists are already seeing pteropods with damaged shells.

This is also true for coral reefs, which are made of calcium carbonate skeletons. To make their skeletons, corals need two ingredients: calcium ions and carbonate ions. Acids react with carbonate ions, in effect making them unavailable.

As the ocean absorbs more carbon dioxide, carbonate ions become scarcer. Corals have to expend more energy to collect them, reducing their ability to build their skeletons. Stanford University scientists have produced a 360-degree virtual underwater ecosystem “to provide an up-close look at how coral reefs might appear by the end of the century if emissions aren’t curbed.”

Marine arthropods also make their shells from calcium carbonate. Crabs, for example, are vulnerable to the changes in ocean chemistry. This toolkit contains information and images about how ocean acidification is impacting Dungeness crab.

This changing ocean chemistry will reverberate through every coastal and marine ecosystem. Read our blog about how and why the waters of the west coast are acidifying more quickly than the global ocean.

Scientists have found that ocean acidification is affecting the way sound is transmitted, which impacts the marine mammals that depend on sound for communication and finding food.

Ocean acidification is affecting shellfish in our diet. Oysters, mussels, scallops, and other shellfish need calcium carbonate to build their shells. With increasing acidity, the shells are thinner, growth is slower and death rates rise. Oyster farmers in the Pacific Northwest are already seeing problems with shell growth in young oysters.

The ocean’s increasing acidification will change the way we eat. The good news is that scientists think that natural genetic variations may help some animals adapt to a more acidic ocean.


Since the industrial revolution, ocean acidity has increased about 30% and it is expected to increase by 100-150% by 2100 if CO2 emissions continue in a business-as-usual scenario.


Scientists working in the Monterey Bay are conducting field studies to see the impact of ocean acidification locally.

Test your knowledge of ocean acidification in this interactive