Role of coral reefs in global ocean production

Abstract

Coral reefs cover some 600 × 103 km−2 of the earth’s surface (0.17% of the ocean surface). First-order estimates show coral reefs to contribute about 0.85% of the estimated net CO2 fixation rate of the global oceans. Gross CO2 fixation is relatively high (about 700 × 1012 gC yr−1), but most of this material is recycled within the reefs. Excess (net) production of organic material (E) is much smaller, about 20 × 1012 gC yr−1. We estimate that 3 × 1012 gC yr−1 (15% of E) is buried in reef structure; 2 × 1012 gC yr−1 (10% of E) for sustained human harvest, and the remaining 75% of E 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 the oligotrophic oceans. Consequently, estimates for global ocean production should include as a first approximation areas of reefs with the surrounding ocean when assigning average net production rates. While there are significant uncertainties in these numbers, we conclude that organic production by reefs plays a relatively minor role in the global scale 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 are either sensitive indicators or accurate recorders of climatic change in most reef systems. Similarly, the productivity of most reefs should be little affected by the environmental changes currently predicted from the Greenhouse Effect.