Linking calcification by exotic snails to stream inorganic carbon cycling

Biotic calcification is rarely considered in freshwater C budgets, despite calculations suggesting that calcifying animals can alter inorganic C cycling. Most studies that have quantified biocalcification in aquatic ecosystems have not directly linked CO₂ fluxes from biocalcification with whole-ecosystem rates of inorganic C cycling. The freshwater snail, Melanoides tuberculata, has achieved a high abundance and 37.4 g biomass m^-2 after invading Kelly Warm Springs in Grand Teton National Park. This high biomass suggests that introduced populations of Melanoides may alter ecosystem processes. We measured Melanoides growth rates and biomass to calculate the production of biomass, shell mass, and CO₂. We compared Melanoides biomass and inorganic C production with ecosystem C pools and fluxes, as well as with published rates of CO₂ production by other calcifying organisms. Melanoides calcification in Kelly Warm Springs produced 12.1 mmol CO₂ m^-2 day^-1 during summer months. We measured high rates of gross primary productivity and respiration in Kelly Warm Springs (-378 and 533 mmol CO₂ m^-2 day^-1, respectively); CO₂ produced from biocalcification increased net CO₂ production in Kelly Warm Springs from 155 to 167 mmol CO₂ m^-2 day^-1. This rate of CO₂ production via biocalcification is within the published range of calcification by animals. But these CO₂ fluxes are small when compared to ecosystem C fluxes from stream metabolism. The influence of animals is relative to ecosystem processes, and should always be compared with ecosystem fluxes to quantify the importance of a specific animal in its environment.