Abstract. Dissolution of anthropogenic CO2 is chronically
acidifying aquatic ecosystems. Studies indicate that ocean acidification
will cause marine life, especially calcifying species, to suffer at the
organism and ecosystem levels. In comparison, freshwater acidification has
received less attention, rendering its consequences unclear. Here, juvenile
Chinese mitten crabs, Eriocheir sinensis, were used as a crustacean model to investigate the
impact of CO2-mediated freshwater acidification. Our integrative
approach, investigating changes in the animal's acid–base homeostasis,
metabolism, calcification, locomotory behaviour, and survival rate,
indicates that this economically relevant crustacean will face energetic
consequences from future freshwater acidification. These energetic
trade-offs allow the animal to maintain its acid–base homeostasis at the
cost of reduced metabolic activity, exoskeletal calcification, and
locomotion, reducing the animal's overall fitness and increasing its
mortality. Results indicate that present-day Chinese mitten crab could be
heavily affected by freshwater acidification like their marine counterparts
and emphasize the importance of understanding the long-term implications of
freshwater acidification on species' fitness.