CONTRIBUTION OF SOFT-BOTTOMS TO THE COMMUNITY METABOLISM (PRIMARY PRODUCTION AND CALCIFICATION) OF A BARRIER-REEF FLAT (MOOREA, FRENCH-POLYNESIA)

The relative contribution of soft bottoms to the community metabolism (primary production, respiration and net calcification) of a barrier r eef flat has been investigated at Moorea (French Polynesia). Community metabolism of the sedimentary area was estimated using in situ incuba tions in perspex chambers, and compared with estimates of community me tabolism of the whole reef flat obtained using a Lagrangian technique (Gattuso et al., 1996. Carbon flux in coral reefs. 1. Lagrangian measu rement of community metabolism and resulting air-sea CO2 disequilibriu m. Mar. Ecol. Frog. Ser. 145, 109-121). Net organic carbon production (E), respiration (R) and net calcification (G) of sediments were measu red by seven incubations performed in triplicate at different irradian ce. Respiration and environmental parameters were also measured at fou r randomly selected additional stations. A model of Photosynthesis-irr adiance allowed to calculate oxygen (O-2), organic carbon (CO2) and ca lcium carbonate (CaCO3) evolution from surface irradiance during a die l cycle. As chlorophyll a content of the sediment was not significantl y different between stations, primary production of the sediment was c onsidered as homogeneous for the whole lagoon. Thus, carbon production at the test station can be modelled from surface light irradiance. Th e modelled respiration was two times higher at the test station than t he mean respiration of the barrier reef, and thus underestimated sedim ent contribution to excess production. Sediments cover 40-60% of the s urface and accounted for 2.8-4.1% of organic carbon excess production estimated with the modelled R and 21-32% when mean R value was conside red. The sedimentary CaCO3 budget was a very minor component of the wh ole reef budget. (C) 1998 Elsevier Science B.V.