Primary production, calcification, and air-sea CO sub(2) fluxes of a macroalgal-dominated coral reef community (Moorea, French Polynesia)

Community metabolism and air-sea carbon dioxide (CO sub(2)) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskaal (Borgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight times m super(-2). Community gross production (P sub(g)), respiration (R), and net calcification (G) were measured in an open-top enclosure. P sub(g) and R were respectively 248 and 240 mmol CO sub(2)/m super(2)/d, and there was a slight net dissolution of CaCO sub(3) (0.8 mmol/m super(2)/d). This site was a sink for atmospheric CO sub(2) (10 plus or minus 4 mmol CO sub(2)/m super(2)/d), and the analysis of data from the literature suggests that this is a general feature of algal-dominated reefs. Measurement of air-sea CO sub(2) fluxes in open water close to the enclosure demonstrated that changes in small-scale hydrodynamics can lead to misleading conclusions. Net CO sub(2) evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a CO sub(2) source) to the study site.