Community metabolism and air-sea CO2 fluxes in a coral reef ecosystem (Moorea, French Polynesia)

In November and December 1991, gross production and respiration were respectively 640.2-753 and 590.4-641.5 mmol (O2 or CO2)m-2d-1 (7.7-9.0 and 7.1-7.7 g C m-2d-1) and the reef displayed a slightly negative excess (=net) production. The contribution of planktonic primary production to reef metabolism was negligible (0.15% of total gross production). Net calcification was positive both during the day and at night; its daily value was 243 mmol CaCO3m-2d-1 (24.3 g CaCO3m-2d-1). Reef metabolism decreased seawater total CO2 by 433.3 mmol m-2d-1. The air-sea CO2 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 (CO2 evasion) at night, decreased as irradiance increased and were negative during the day (CO2 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 mmol m-2d-1).