Anthropogenic CO<sub>2</sub>-mediated freshwater acidification limits survival, calcification, metabolism, and behaviour in stress-tolerant freshwater crustaceans

Abstract

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.

Elevated dissolved carbon dioxide and associated acidification delays maturation and decreases calcification and survival in the freshwater crustacean Daphnia magna

“…Other potential mechanisms explaining the reduced calcium content we observed could involve energetic limitations resulting from acid–base disturbance and metabolic depression, solubilization of the carapace to buffer the hemolymph, or altered calcium transport processes (Quijada‐Rodriguez et al 2021; Tripp et al 2022). More detailed experiments in which, for example, calcium uptake rates are quantified or the calcium metabolism is explored further under different pCO 2 and Ca 2+ levels will be required to determine the underlying mechanism of pCO 2 on calcification in planktonic freshwater crustaceans.…”

“…Responses of freshwater organisms to elevated pCO 2 and associated acidification are still poorly understood. Earlier exploratory work on freshwater decapod crustaceans suggests that species with highly calcified carapaces can be sensitive (Beaune et al 2018; Quijada‐Rodriguez et al 2021) and that even a modest pH reduction (pH 5.5–7.0), which is typically associated with elevated pCO 2 (Hasler et al 2018), could impair calcification. The existence of similar responses in planktonic freshwater crustaceans, however, remained largely unexplored.…”

“…For instance, pCO 2 levels in freshwater and associated changes in pH are determined by the input of allochthonous organic matter and rates of terrestrial respiration (Cole et al 2007; Hasler et al 2016). Therefore, pCO 2 predictions for freshwater systems are variable and case‐specific (Phillips et al 2015; Quijada‐Rodriguez et al 2021). Nonetheless, most freshwater ponds and lakes are supersaturated in pCO 2 (Cole et al 2007; Raymond et al 2013) and values of up to 23,000 ppm have already been recorded in shallow freshwaters in temperate regions (Abril et al 2015; Holgerson 2015; overview see Appendix Table S1).…”

“…However, to date, the impact of elevated pCO 2 on calcification has only been studied in a limited number of freshwater invertebrates. Effects of elevated pCO 2 include reduced calcification rates in the Chinese mitten crab (Quijada‐Rodriguez et al 2021) and a decrease in biomineralization regulators in a unionid mussel species (Jeffrey et al 2018). In a freshwater crayfish, no effect of pCO 2 on carapace Ca 2+ levels was found (Tripp et al 2022).…”

“…magna . The reason for this might be energetic constraints or possibly problems with calcium uptake (Beaune et al 2018; Quijada‐Rodriguez et al 2021). Previous experiments that exposed zooplankton to increased pCO 2 did not find strong effects on life history (Urabe et al 2003; Weiss et al 2018) but this is probably because they were short trials (7 d).…”