Common periwinkles consumed less food when living under ocean acidification conditions for five weeks, after having been exposed to those conditions for two weeks prior to the experiment. Their food—a biofilm of diatoms, cyanobacteria, and various microbes—increased during that period. However, another group of periwinkles consumed more food than the first group; they had been exposed to ocean acidification for a longer time period (five months rather than two weeks) before the experiment began. The study underscores the challenges of predicting future changes in the ocean ecosystem based on short-term experiments, asvariations in exposure time and other aspects of the artificial setting can affect the observed outcomes. (Laboratory study)