Lots of commercial fisheries use lime to reduce the levels of algae and if used in correct quantities does not affect the fish. If the sea is becoming acidic, then by neutralising this then it should surely benefit the aquatic wildlife considerably.
There was an item on the radio about this recently. Sea water is naturally alkaline, but with pollution is becoming less so. However, even in a worse case scenario it would not become acidic. It was suggested that lime be added to maintain the pH, so as to not endanger fish stocks.