Secondary production, calcification and CO₂ fluxes in the cirripedes Chthamalus montagui and Elminius modestus

Abstract

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 ${\text{1,803}}{\text{.9}}\,{\text{g}}_{{{\text{CaCO}}_{{\text{3}}} }} \,{\text{m}}^{{ - 2}} \,{\text{year}}^{{ - 1}}$ at each site, representing 3.4 and ${\text{12}}{\text{.7}}\,{\text{mol}}_{{{\text{CO}}_{{\text{2}}} }} \,{\text{m}}^{{ - 2}} \,{\text{year}}^{{ - 1}}$ 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.