Seawater carbonate chemistry and calcification during a tropical lagoon study at Uvea lagoon, New Caledonia, 1995

Tropical ecosystem understanding is related to reef compartment functioning and to a lesser extent to mangrove systems. Reef metabolic budget is considered to be approximatively balanced with a very weak net production in spite of a large gross production (Crossland et al., 1991 ; Gattuso et al., 1993) when carbon export of inangroves to adjacent systems appears more and more problematic (Alongi & Christoffersen, 1992). As a consequence, structuring mechanisms of the vast stretch of sedimentary bottoms found in most lagoons is still misunderstood. These biogenic accuniulation of particules, up to now considered as the result of reef exportation, and to a lesser extend to mangrove input, have focussed little attention as far as the carbon budgets are concerned (Sorokin, 1993). Rare studies were obtained from oxygen measurements transformed in carbon by the way of metabolic quotients previously calculated in temperate ecosystems or even on planctonic organisms. Such an approach is conceivable in preliminary studies but needs an improvement to balance coral reef udget. Our research constitute an adaptation of carbon bugdet investigations undertaken in temperate marine sediments by Hargrave & Phillips (198 1) to coral systems.