Ocean Acidification

Carbon dioxide in the water puts shelled animals at risk.

For tens of millions of years, Earth's oceans have maintained a relatively stable acidity level. It's within this steady environment that the rich and varied web of life in today's seas has arisen and flourished. But research shows that this ancient balance is being undone by a recent and rapid drop in surface pH that could have devastating global consequences.

Source:  https://www.nationalgeographic.com/environment/oceans/critical-issues-ocean-acidification/