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ABSTRACT-Community metabolism was investigated uslng a Lagrangian flow resplrometry technique on 2 reef flats at Sloorea (French l'olynesia) during austral winter and Yonge Reef (Great Barrier Reef) during austral summer. The data were used to estimate related air-sea CO, disequilibrium. A slne funct~on did not sdtisfactorily model the d~e l light curves and ov~rrstsmated the metabolic parameters.The ranges of community gross primary production and respirat~on (P,, and R, 9 to 15 g C m-? d-') were within the range previously reported for reef flats, and community net calcification (G; 19 to 25 g CaCO, m-2 d.') was higher than the 'standard' range. The molar ratio of organlc to inorganic carbon uptake was 6:l for both sites. The reef flat at hdoorea displayed a higher rate of organic production and a lower rate of calcification compared to previous measurements carried out during austral summer. The approximate uncertainty of the daily metabolic parameters was estimated using a procedure based on a Monte Carlo simulation. The standard errors of P,, R and R,IR expressed as a percentage of the mean are lower than 3 % but are colnparat~vely larger for E, the excess production (6 to 78'1;, INTRODUCTIONThe biological processes controlling the CO2 partial pressure in seawater ( p C 0 2 ) and, consequently, the air-sea CO2 fluxes are net organic production and calcification, which have opposite effects on pC02. Coccolithophorid blooms and coral reefs are the major marine photosynthetic and calcifying systems and are, therefore, well suited to studies of the interactive 'E-mail: gattuso@naxos.unice.fr "Present address: Un~versiti. de Liege, Mecanique des Flu~des Geophysiques, Unite d'oceanographie Chimique, Institut d e Physique (B5). 8-4000 Sart Tilman, Belglum effects of photosynthesis-respiration and precipitation-dissolution of calcium carbonate on the seawater CO2 system and air-sea CO2 fluxes. Coccolithophorid blooms are transient (Holligan et al. 1993), annually cover on average 14 X 105 km2 of the world's oceans (Brown & Yoder 1994) and have been shown to behave as sources for atmospheric CO, (Robertson et al. 1994). Coral reefs are permanent, long-lived ecosystems covering 6 X 105 km2 (Smith 1978a). There is a rather large set of data on reef community lnetabolism (Kinsey 1985, Smith 1995 but very few estimates of air-sea CO2 fluxes in coral reefs . In most reefs investigated, gross primary production (Pg) and respiration (R) are nearly balanced (P,/R = 1) and netResale of full article not perrnltted

Community metabolism (primary production, respiration and calcification) and air-sea CO2 fluxes of the 'Tiahura barrier reef' (Moorea, French Polynesia) were investigated in November and December 1991 Gross production and respiration were respectively 640.2 to 753 and 590.4 to 641.5 mm01 (02 or CO2) m-' d-l (7.7 to 9.0 and 7.1 to 7.7 g C m-2 d ') and the reef displayed a slightly negative excess (= net) production. The contribution of planktonic primary production to reef metabolism was negligible (0.15 ?4, of total gross production). Net calcification was positive both during the day and at night; its daily value was 243 mm01 CaCO, m-2 d -' (24.3 g CaC03 m m 2 d-l). Reef metabolism decreased seawater total CO2 by 433.3 mm01 m--d-' The air-sea CO, fluxes were close to zero in the ocean but displayed a strong daily pattern at the reef front and the back reef. Fluxes were positive (COz evasion) at night, decreased as irradiance increased and were negative during the day (COz invasion) Integration of the fluxes measured during a 24 h experiment at the back reef showed that the reef was a source of CO2 to the atmosphere (1 5 minol m-2 d-l).

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