Productivity of Enewetak Atoll reef flats predicted from mass transfer relationships

Abstract

The productivity of a coral reef flat at Enewetak Atoll is calculated by assuming phosphate (P) uptake is mass transfer limited, and then scaling P uptake to carbon (C) fixation. The approach is to treat the coral reef flat as a rough surface in fully-developed turbulent flow. Input parameters to the equations are water velocity, depth, roughness height of the reef, P concentration and the C:P ratio of autotrophs. A 9-day continuous record of water velocity and depth over the windward reef flats of Enewetak Atoll is used to compare an estimate of productivity from the model to the measured productivity. The calculated productivity is 542 ± 79mmol C m −2 day −1 and the measured productivity is 500 mmol C m −2 day −1. Although there are few experiments to verify empirical scaling of engineering equations to reef communities, these results indicate that neither alternative external supplies of P, nor biological mechanisms of recycling appear to be required to support the high areal productivity of the Enewetak reef flats. A high flow rate of tropical surface water across reef flats can account for the elevated productivity of these communities.