Carbon and carbonate metabolism in coastal aquatic ecosystems

The coastal zone is where land, ocean, and atmosphere interact. It exhibits a wide diversity of geomorphological types and ecosystems, each one displa ying great variability in terms of physical and biogeochemical forcings. De spite its relatively modest surface area, the coastal zone plays a consider able role in the biogeochemical cycles because it receives massive inputs o f terrestrial organic matter and nutrients, is among the most geochemically and biologically active areas of the biosphere, and exchanges large amount s of matter and energy with the open ocean. Coastal ecosystems have therefo re attracted much attention recently and are the focus of several current n ational and international research programs (e.g. LOICZ, ELOISE). The prima ry production, respiration, calcification, carbon burial and exchange with adjacent systems, including the atmosphere, are reviewed for the major coas tal ecosystems (estuaries, macrophyte communities, mangroves, coral reefs, and the remaining continental shelf). All ecosystems examined, except estua ries, are net autotrophic. The contribution of the coastal zone to the glob al carbon cycle both during pristine times and at present is difficult to a ssess due to the limited metabolic data available as well as because of maj or uncertainties concerning the magnitude of processes such as respiration, exchanges at the open ocean boundary, and air-sea fluxes of biogases.