Here is a report on the topic of ocean acidification:
When CO2 is released into the atmosphere, it will often be absorbed into water. The water will then sort it out. This has been going on for a very very long time. Unfortunately, human activity has significantly increased the amount of CO2 put into the atmosphere, causing drastic effects.
When CO2 encountered H2O, it will often bond to form carbonic acid! That is why it is known as ocean acidification (the definition of an acid is something that releases H+ions into a solution). When CO2 and H2O bond, they expel spare H+ions that are attracted to H2O.
The water with extra H+ions will lure essential bonds out of calcium carbonate, what shells are made of, and make the molecules come off and dissolve the shell! This causes the shelled organism to die off, causing eaters of those to eat other stuff or die off, causing fish to become scarce, causing the fish market to completely die off (though it would be great if people didn’t fish very much).
And now, here is a video about it: