As carbon dioxide (CO2) dissolves into seawater, the seawater becomes more acidic. This process is called ocean acidification. As human and other activities release carbon dioxide into the atmosphere, the ocean absorbs the CO2.
The following description taken from the website, http://www.ocean-acidification.net/FAQacidity.html gives a simple explanation of why this matters.
“When CO2 dissolves in seawater, it forms carbonic acid, which releases hydrogen ions into solution. Acidity is a measure of the hydrogen ion concentration in the water, where an increase in hydrogen leads to an increase in acidity (and a decrease in the pH scale used to quantify acidity). These hydrogen ions then combine with carbonate ions in the water to form bicarbonate. Carbonate ions are the basic building blocks for the shells of many marine organisms. Thus the formation of bicarbonate through this chemical reaction removes carbonate ions from the water, making them less available for use by organisms. The combination of increased acidity and decreased carbonate concentration has implications for many functions of marine organisms, many of which we do not yet fully understand.”
Organisms that form shells form an important component of the human food system and natural food web. In the Skagit and Samish Bays shellfish and crabs are some important economic and cultural foods that humans both enjoy and rely upon. Organisms such as ??? are an important basis of the Skagit basin marine food web that could be potentially impacted by ocean acidification.