This is actually happening in our world now due to more CO2 being released in the air every second. First of all, it would change balances of chemicals by a lot. The ocean's PH would be skyrocketing, and that would mean bad things for marine life. Second of all, animals with shells are already experiencing their shells rapidly disintegrating, and that limits their ability to protect themselves. Soon enough, animals without shells and just gills might just start going extinct.