The oceans are helping to absorb carbon dioxide -- but it's harming marine life.

What is ocean acidification?

Ocean acidification occurs when carbon dioxide emitted into the atmosphere via human activities is absorbed by the ocean. When CO2 combines with water in the ocean, carbonic acid is formed, which lowers (creates a more acidic) pH.

Remind me: what’s pH?

pH is a measure of acidity or alkalinity. A pH below 7 is considered acidic, and a pH greater than 7 is considered alkaline, or basic. The pH scale is logarithmic, so a one point change on the scale means a tenfold change in concentration.

The oceans are slowing global warming – but it’s harming marine life.

Ocean acidification is a phenomenon that has been occurring for several decades --- in fact, ocean acidity has increased by 26% since the Industrial Revolution – this is 10 times faster than any period within the last 55 million years!

Oceans absorb between 30-50% of the CO2 that humans release into the atmosphere, which has led to a change from 8.2 to 8.1.

How does ocean acidification affect marine life?

This change in ocean pH impacts different metabolic, respiratory, reproductive, and other natural processes of all marine organisms.

The most affected species are phytoplankton, coral reefs, and a great variety of shellfish and mollusks – all organisms that are key to the presence of life within the marine ecosystem.

The most threatened species are coral reefs and those with skeletons and shells, since they use the calcium present in seawater to develop the shell. When the ocean has an acidic pH, it is almost impossible for living organisms to absorb calcium, which is what creates their shells.

Therefore, corals, crabs, clams, oysters and marine snails are the most endangered species – and their endangerment will impact higher levels of the food chain that depend on them for sustenance, such fish, whales, and birds.

how does ocean acidification affect coral?

25% of marine species could disappear if corals die out. 

A recent WHOI study has shown that ocean acidification particularly impedes the coral’s thickening process—decreasing the skeletons’ density and leaving them more vulnerable to breaking.

Coral skeletons are composed of a form of calcium carbonate called aragonite. Corals grow by stacking crystals of these aragonite on top of each other, while thickening to them horizontally to withstand potential breakage resulting from waves, storms, currents, and general wear & tear resulting from mollusk and fish activity.


Carbon dioxide (CO2) is absorbed by seawater, setting in motion chemical reactions that produce bicarbonate (HCO3–) and carbonate (CO32-) ions.

Coral polyps—the soft-bodied corals—bring in seawater containing HCO3–, CO32- and calcium (Ca2+) ions into a “calcifying space” between its cells and the surface of the existing skeleton. They pump hydrogen ions (H+) out of this space to produce more carbonate ions (CO32-) ions, making it easier to make calcium carbonate (CaCO3) for their skeletons. But when the oceans absorb excess CO2, as is happening now, there are more HCO3– ions but fewer CO32- ions in seawater, making it harder for corals to build up their skeletons.

Up to one-quarter of all marine species depend on coral reefs as a refuge, spawning area, and food source. Therefore, there will be an accelerated decline in fish and crustacean populations that will directly affect the world's food security.


Seafood is an important source of protein for millions of people, and is also the livelihood of the 120 million people employed by the fishing industry.

At this rate, by 2100, the global annual costsof mollusk loss alone from ocean acidification could be over US $100 billion.

Additionally, the more CO2 the ocean absorbs now, the less it will be able to absorb in the future.


Plastic pollution absolutely contributes to the increased acidity in the ocean.

A recent study found that pollution from plastic waste in the oceans is correlated with ocean acidification, as the plastic essentially creates a novel habitat for distinct microbial communities that are harmful to coral and sea life to flourish. 

The study found that as CO2 increased, bacterial distribution accelerated – it also found that 350 groups of the bacteria examined were unique to plastics, many of which negatively impacted other bacteria that play an important role in carbon cycling (in other words, they help reduce acidification)

how can ocean acidification be prevented?

The best way to prevent and reduce ocean acidification is to reduce our CO2 emissions and energy consumption at work and at home.

For example, we can change the type of light bulbs we use to energy saving ones, and switch off electronic devices at night. We can also buy products that are environmentally friendly and whose production method does not generate CO2 emissions.

Taking it further, we can also take measured to go plastic-free (we are!) with more reusable models than recycling (because only 9% of recycled material actually gets recycled in the US!), and use bio-friendly cleaning products that don’t harm the water supply.