Final answer:
Ocean acidification, caused by increased CO2 levels, creates an environment where shellfish have trouble forming their calcium carbonate shells, leading to (b) decreased shell formation.
Step-by-step explanation:
Ocean acidification refers to the process where increased amounts of atmospheric CO2 are absorbed by the ocean, leading to a decrease in pH levels and causing the water to become more acidic. This acidification of the ocean impacts marine life, particularly organisms that rely on calcium carbonate for their shell and skeleton formation, such as shellfish and corals. Due to the lower availability of carbonate ions necessary for the formation of calcium carbonate, shellfish are experiencing decreased shell formation.
When atmospheric CO2 levels rise, the additional CO2 dissolved in ocean water results in an increase in hydrogen ion concentration, which decreases the pH, and makes the ocean more acidic. This acidic environment hinders the absorption of calcium and carbonate ions, crucial for the creation of aragonite, a mineral that forms the shell and skeletal structures in marine organisms.
An aragonite deficit has already been recorded in many parts of the world's oceans, indicating that shellfish and other marine organisms with calcium carbonate structures are being adversely affected by the changing chemistry of seawater.