AP Environmental Science 5.J: Overfishing

Coral reefs are produced when corals acquire calcium ions $\left(\mathrm{Ca}^{2+}\right)$ and carbonate ions $\left(\mathrm{CO}_{3}{ }^{2-}\right)$ from seawater and deposit solid $\mathrm{CaCO}_{3}$ to form their exoskeletons. Scientists are concerned that relatively rapid decreases in ocean water pH will hinder the deposition of $\mathrm{CaCO}_{3}$. The graph above shows the amount of $\mathrm{CO}_{2}$ dissolved in ocean water and ocean water pH (shown in parentheses) since 1850 and the predicted changes through 2100.

Identify one environmental problem (other than one due to ocean acidification or loss of coral reefs) that affects marine ecosystems on a global scale.