ROLE OF CORAL REEFS IN GLOBAL OCEAN PRODUCTION

Coral reefs cover some 600 thousand square kilometres of the earth's surface (0.17% of the ocean surface). First order estimates show coral reefs to contribute about 0.05% of the estimated net CO2 fixation rate of the global oceans. Gross CO2 fixation is relatively high (of the order 700 x 10(12) g C year-1), but most of this material is recycled within the reefs. Excess (net) production of organic material (E) is much smaller, of the order 20 x 10(12) g C year-1. We estimate that 3 x 10(12) g C year-1 (15% of E) is buried in reef structure, 2 x 10(12) g C year-1 (10% of E) is available for sustained human harvest, and the remaining 75% of E is available for export from coral reefs to adjacent areas. Comparison of estimates for net production by reefs and their surrounding oceans indicates that the excess production by coral reefs is similar to new production in the photic zone of oligotrophic oceans. Consequently, estimates for global ocean production should as a first approximation include reefal areas with the surrounding ocean when assigning average net production rates. While there are significant uncertainties in these numbers, it can be concluded that organic production by reefs plays a relatively minor role in the global scale of fluxes and storage of elements. In comparison, the companion process of biologically-mediated inorganic carbon precipitation represents a major role for reefs. While reef production does respond on local scales to variation in ocean climate, neither the absolute rates nor the amount accumulated into organic pools appear to be either sensitive indicators or accurate recorders of climatic change in most reef systems. Similarly, the productivity of most reefs should be little affected by currently predicted environmental changes resulting from the Greenhouse effect.