Ocean acidification has been called global warming's evil twin. Like warming, acidification is caused by human greenhouse gas emissions and has the potential to reshuffle the ecological deck in the ocean. Unlike warming, however, near-future changes in pH will exceed anything in the recent geological record, and there are few if any places to hide. I will discuss the many ways in which ocean acidification affects marine species, including shellfish that we eat and kelps and invertebrates that define key marine habitats. I will emphasize the importance of moving beyond studies of single species studies, and present examples of how ocean acidification may change coastal ecosystems in British Columbia and beyond.