You see, sometimes our factory pollutants just don't go up in the air, but also to our oceans. When the gasses meet the sea, these disolve and decrease the pH level of our planet's oceans. ANd not just that, possible from oil leaks, and coal byproducts getting to the sea, sewage, and etc.
These effects are tremendous, ranging in to destroy the very rainforests of the sea. The coral reefs, that protect marine life in storms and predators, to sea water fish that don't go to fresh water which then get unable to live.
http://www.youtube.com/watch?v=5cqCvcX7buo&feature=player_embedded