Increased Carbon Dioxide (CO2) in the atmosphere is causing ocean acidification.
According to biologicaldiversity.org, "Every day, 22 million tons of carbon dioxide from factories, cars, power plants and other human sources are absorbed by the world's oceans."
"The oceans have become 30% more acidic because of the carbon population we're pumping into the atmosphere."
As a result, coral reefs are collapsing...
...oyster beds are disappearing...
...and shellfish are unable to protect themselves. Ocean acidification "...robs seawater of the compounds these creatures need to build shells and skeletons, impairing their development and, ultimately, their survival." If shellfish populations collapse, the food web will suffer greatly.
Lastly, ocean acidification makes seawater more acidic...this is a major disaster for marine animals up the food chain, and eventually will be a huge problem for us, who rely on oceans for food. The effect could be catastrophic.