Résumé
Calcification, a process common to numerous marine taxa, has traditionally been considered to be a significant source of CO2 in tropical waters only. A number of relatively recent studies, however, have shown that significant amounts of CO2 are also produced in temperate waters, although none of these studies was carried out on rocky shores, which are considered to be very productive systems. We compared the CO2 fluxes due to respiration and calcification in two temperate species, the cirripedes Chthamalus montagui and Elminius modestus. The population dynamics of both species were estimated at two sites during a 1-year experimental period in order to establish mean organic (ash-free dry weight) and CaCO3 (dry shell weight) production. Based on these parameters, we estimated the CO2 fluxes due to respiration and calcification. CaCO3 production was estimated to be 481.0 and 1,803.9 g(CaCO3) m(-2) year(-1) at each site, representing 3.4 and 12.7 mol(CO2) m(-2) year(-1) respectively, of released CO2. These fluxes represent each 47% of the CO2 released as a result of respiration and calcification. The production of CaCO3 at the high-density site was: (1) among the highest values obtained for temperate organisms, and (2) comparable to the estimated CO2 fluxes for coral reefs. As calcifying organisms are well represented in temperate ecosystems in terms of both density and biomass, our results provide clear evidence that calcification of temperate organisms should not be underestimated. Additional studies on other rocky shore taxa are needed before the relative importance of calcification in rocky intertidal carbon budgets can be generalized.