9306381 THOMAS This project addresses the question of how coral reef communities maintain high productivity in regions of nutrient depleted waters. Work by Atkinson has demonstrated that by assuming phosphate (P) uptake is mass transfer limited, productivity can be predicted from physical parameters (i.e. P concentration, water velocity, water depth, and bottom roughness). To make these predictions, Atkinson has developed a model that uses correlations of mass transfer to engineering type surfaces from engineering literature. A scaling parameter is used to adjust these correlations for the biologically rough surfaces of coral reef communities. The value for this scaling factor (6.4) is based on measurements of nutrient uptake to coral reef communities. Without this scaling factor, engineering correlations do not accurately predict rates of mass transport of nutrients into coral reef communities. The difference between the rates of mass transfer predicted by engineering correlations and those empirically measured are likely due to the differences between the types of surfaces used in the experiments. Engineering data have been obtained for surfaces that are rough on a single spatial scale while the roughness of biological surfaces can occur at multiple scales. Rates of mass transfer into rough surfaces are a function of both roughness and the friction coefficient of the community. To accurately quantify the relationship between mass transfer of nutrients and productivity in coral reef communities, it is essential that we be able to measure both of these parameters for coral reef communities. The primary goal of this research project is to develop techniques to measure the surface roughness of coral reef communities and to determine how this roughness affects their friction coefficients. These measurements in combination with measurements of nutrient transport within experimental reef communities will provide the data necessary to develop a larger proposal for a theoretical model that links mass transfer with productivity in coral reef communities. The objectives of this project are: 1) to empirically measure friction coefficients for coral reef communities that vary in their degree of roughness; 2) to develop a biologically relevant measurement of community roughness; 3) to correlate these roughness measurements with the measured friction coefficients; and 4) to determine the relationships between the measured friction coefficients, roughness parameters, and enhancement of mass transfer. ***
