Final answer:
Ocean acidification, caused by increased atmospheric CO2, lowers the ocean's pH and hinders shell and exoskeleton formation in marine organisms.
Step-by-step explanation:
Acids affect the shells of sea creatures such as mollusks, corals, and plankton by decreasing the pH of ocean water, a process known as ocean acidification. When the concentration of atmospheric carbon dioxide (CO2) increases, more CO2 dissolves in the ocean, forming carbonic acid which leads to lower pH levels.
This increased acidity inhibits the absorption of calcium and carbonate ions, which are crucial for the formation of calcium carbonate, the substance that makes up the shells and exoskeletons of these marine organisms. The reduction in availability of calcium carbonate as a result of ocean acidification results in weaker and thinner shells.
For example, organisms like pteropods are already experiencing shell dissolution while still alive. Coral reefs, which are made up of countless coral polyps with calcium carbonate exoskeletons, are also severely impacted and are at risk of declining calcification rates, potentially leading to a significant decrease in reef structures by 2050.