How is Acidification Harmful?

The pH scale goes from 0 to 14; lower numbers on the scale mean a solution is more acidic, higher numbers indicate the solution is more basic, a pH of 7 means the solution is neutral. The ocean has had a pH of around 8.2 in the past, and presently it is about 8.1, indicating about a 30% increase in acidity.

When CO2 is absorbed by the ocean, carbonic acid forms. This causes acidity levels to rise due to the drop in pH. Creatures that need to produce calcium carbonate shells or skeletons, such as clams, oysters, urchins and corals, are negatively affected by high CO2 absorption; carbonic acid inhibits their ability to grow shells and make the basic skeletons needed to live.
Want to read more detail about the chemistry of ocean acidification? Look here: What is Ocean Acidification? The Chemistry