Actually, calcifying plankton have been increasing 10x in abundance (i.e. an order of magnitude) in the North Atlantic over the last 45 years, as carbon input into ocean waters has increased. ... "This finding was diametrically opposed to what scientists had expected since coccolithophores make their plates out of calcium carbonate, which is becoming more difficult as the ocean becomes more acidic and pH is reduced." [1]
[1] https://www.sciencedaily.com/releases/2016/01/160116215419.h...