2. Global warming
Global warming has an enormous effect on the oceans. About 30 to 40% of the carbon dioxide we release in the atmosphere dissolves into the sea, rivers, and lakes. It reacts with the water to form carbonic acid and starts a process called ocean acidification, which is slowly but surely making the water more acidic.
This affects all kinds of creatures but is particularly harmful to those with hard shells, such as crustaceans as the acid eats away this protective layer.