That is chemically correct. However, carbonic acid is a very weak acid, which means that the chemical balance you posted would be very tipped towards the left member. I honestly don't know what is the tolerance of oceanic life with regards to changes in the pH of the water (I suspect it's quite low), but I think that given the size of the oceans, you would really need to dissolve a lot of CO2 in order to significantly change its acidity. In addition, I think I heard that the oceans have their own mechanisms to control acidity changes.
I am by no means an expert, and all of that is based on my rather limited knowledge of chemistry. That, added to the fact that I lack any figures to back it up, makes me wonder why am I writing this reply at all...