Scaling-up carbon and carbonate metabolism of coral reefs using in-situ data and remote sensing

Areal up-scaling at reef-scale of organic and inorganic metabolism is possi ble using in-situ measurements and remote sensing data providing the extent of each bottom type inside the reef. Using a SPOT image and published valu es of metabolism, the gross production (93,560 x 10(3) kg C year(-1)), exce ss production (10,017 x 10(3) kg C year(-1)) and calcification (165,348 x 1 0(3) kg CaCO3 year(-1)) over 35 km(2) of coral reef environment in Moorea I sland (French Polynesia) are estimated. While the computations are straight forward, certain assumptions must be made in order to conduct the scaling e xercise. The exercise is valid only if the metabolism of reef benthos is ad ditive through increasing spatial scale. Despite the difficulty of quantita tively assessing our extrapolations, spatial additivity seems to represent the reality. The other limitation is that the reef must be considered as a closed system, in an equilibrium state supposedly accurately described by t he few available in-situ measurements. To consider the reef an open system, long-term metabolic measurements coupled with knowledge of oceanic and lan d forcing processes are required. These theoretical considerations point to the necessity of integrated multi-scale studies based on both remote sensi ng and in-situ data in order to better understand the productivity and calc ification of reefs in the current global change context.