Corals of Australia's Great Barrier Reef Click on image for full size (220 Kb) Courtesy of UNC

Increasing amounts of carbon dioxide are released into the atmosphere from burning of fossil fuels. Some of that carbon dioxide makes its way into the world’s oceans. This changes the chemistry of seawater, lowering its pH, making it more acidic, which could have a large impact on marine life in the future.

Marine creatures such as corals, clams, snails, and many types of algae and plankton build their skeletons and shells from calcium carbonate. These creatures get the chemical building blocks they need to form the calcium carbonate mineral of their skeletons from seawater. As seawater gets more acidic with more carbon dioxide dissolved in it, these creatures might have a harder time making their skeletons and shells.

Calcium carbonate mineral dissolves in acid. Try it out for yourself. Put a clam shell (one that you don’t want to keep) into a container of vinegar and wait. Vinegar is an acid. Within a few hours will notice that your clam shell is disappearing. The calcium carbonate that makes up the shell is dissolving into the acidic vinegar.

Seawater's pH is not dropping as low as vinegar. Vinegar has a pH of about 3. The pH of seawater varies between 7 and 8, so it is a little more basic than neutral. Since the start of the Industrial Revolution, pH of seawater has dropped about 0.1. In the next century it is expected to drop another 0.1-0.35. But scientists suspect that even these small changes can make a big difference to the creatures that need to build their shells.

Because reef corals build massive structures from calcium carbonate, and because those structures become a home to diverse communities of marine life, the impact of increasing acidification on corals is of particular interest to many scientists.

The current research indicated that for a doubling of the partial pressure of carbon dioxide (pCO2), rates of calcification decreased in corals an average of 30%. The rate is affected by many other factors besides the concentration of CO2 dissolved in the water. The temperature, light, and nutrients all affect calcification rates too.

Lower rates of calcification will likely impact marine food webs, possibly changing the biodiversity of the ocean.

Corals of Australia's Great Barrier Reef Click on image for full size (220 Kb) Courtesy of UNC

Some of the carbon dioxide that is added to the atmosphere from burning fossil fuels makes its way into the world’s oceans. This makes seawater more acidic, which could have a large impact on marine life.

Marine creatures such as corals, clams, snails, and many other types of marine life build their skeletons and shells from calcium carbonate. These creatures get the materials they need to make the calcium carbonate from seawater. As seawater gets more acidic these creatures might have a harder time building their skeletons and shells because calcium carbonate mineral dissolves in acid.

Put a clam shell (one that you don’t want to keep) into a container of vinegar and wait. Vinegar is an acid. Within a few hours will notice that your clam shell is disappearing. The calcium carbonate that makes up the shell is dissolving into the acidic vinegar.

Seawater will not become as acidic as vinegar. It has become only slightly more acidic over the past 150 years. It will continue to get more acidic, but very slowly. Scientists suspect that even a small change can make a big difference to the creatures that need to build their shells.

Because corals build reefs from calcium carbonate, and because those reefs become a home to a large amount of marine life, scientists are especially interested in the impact of more acidic water on corals.

Slower growing shells and skeletons can have an impact on the food webs of marine life, possibly changing the number of species of living things in the ocean.

Corals of Australia's Great Barrier Reef Click on image for full size (220 Kb) Courtesy of UNC

Even the clams and corals that live at the bottom of the sea are affected by greenhouse gases in the atmosphere. That’s because there’s a greenhouse gas that is getting into the ocean. Carbon dioxide gets into the air when we burn oil, coal, and gas. And it can become dissolved in seawater. This makes the oceans more acidic, which could spell trouble for ocean life because the mineral of their shells dissolves in acid.

Seawater has become only slightly more acidic over the past 150 years. It will get more acidic in the future, but very slowly. Even this small change can make a big difference for many different types of ocean life.

Scientists are very interested in learning more about how this will affect corals. Corals build large reefs that become a home for so many other animals. If corals can't grow the reef, then many animals might not be able to find a reef home.