An amphibious mode of life in the intertidal zone : aerial and underwater contribution of Chthamalus montagui to CO2 fluxes

The contribution of the intertidal barnacle Chthamalus montagui to CO2 fluxes via respiration and calcification was measured both in the air and underwater. The mean biomass of the species was 44.92 g ash-free dry weight (AFDW) m?2 on the coast of Brittany, France. Underwater respiration, determined from changes in dissolved inorganic carbon (DIC), fluctuated from 6.14 µmol g?1 h?1 in winter to 13.37 µmol g?1 h?1 in summer. The contribution of C. montagui respiration to DIC fluxes for an average daily immersion time of 8 h was 3.21 mmol m?2 d?1. Mean aerial CO2 respiration was estimated at 7.60 µmol g?1 h?1 using an infrared gas analyser, corresponding to 5.46 mmol m?2 d?1 if the mean daily emersion time is 16 h. Net calcification was positive, with a mean value of 1.01 µmol g?1 h?1, corresponding to a CO2 flux of 0.25 mmol m?2 d?1. The total mean daily emission of CO2 by C. montagui populations was 8.92 mmol m?2 d?1. The annual carbon production by the species was 39.07 g m?2 yr?1 with relative contributions by aerial respiration, underwater respiration and net calcification of 61, 36 and 3%, respectively. The daily ratio of aerial:underwater carbon emission was 1.7, emphasizing the prevalence of aerial respiration and the metabolic adaptation of C. montagui to amphibious life