A ubiquitous type of phytoplankton — tiny organisms that are the base of the marine food web — appears to be suffering from the effects of ocean acidification caused by climate change. According to authors of a new study, the single-celled organism under study is a type of “calcifying” plankton called a coccolithophore, which makes energy from sunlight and builds microscopic calcium carbonate shells, or plates, to produce a chalky suit of armor.