In fact, the fossil record shows planktic foraminifera building smaller, thinner shells before they vanished. GOING THROUGH CHANGES: These scanning electron microscope images show planktic foraminifera from before (bottom) and after (top) the Aptian-Albian extinction event. The only problem with the ocean acidification explanation is that benthic foraminifera, which live in deeper ocean waters, didn’t seem to be affected. The planktic foraminifera shells revealed slower calcification, a tell-tale sign of ocean acidification. The excess alkalinity circulated through the water column, making it available for benthic foraminifera living on the seafloor.