Fig. 1. Diagrammatic representation of the pathways of carbon fixed in coral reef ecosystems (after Done et al. 1996). Total productivity (rate of carbon accumulation in organic and inorganic compartments) is a function of solar radiation, its rate of attenuation through the water column (a function of water clarity) and incoming nutrients and organic matter. The relative sizes of compartments and the fluxes between compartments (thickness of arrows) are mediated by local abundances of organisms. All thus vary with reef location and with depth and zone on an individual reef. Humans, through individual and synergistic pressures of climate change, fishing and pollution can also affect compartments.