Blue mussels grew and calcified 7 times faster in the Kiel Fjord (Baltic Sea), where low pH (ocean acidification) conditions prevailed, than at an outer fjord site where pH levels were higher In addition, the mussels were able to outcompete barnacles at the inner fjord, low pH site. Thus, blue mussels can dominate over a seemingly more acidification-resistant species such as barnacles. High mussel productivity at the inner fjord site was enabled by high availability of food particles (organic carbon). The researchers concluded that adult blue mussels tolerate ocean acidification when food supply is abundant and that ecosystem characteristics such as species interactions and food availability need to be considered to predict species vulnerability to ocean acidification.