Phosphate-uptake of experimental coral and algal communities under steady versus Oscillatory Flow

Abstract

Relationships between nutrient-uptake and net carbon production are variable on reefs. Nutrient-uptake appears to be governed by diffusion of nutrients through nutrient-depleted boundary layers near the surfaces of autotrophs. Nutrient-uptake may occur at different rates under steady and oscillatory flows because the boundary layers may be different. Rates of phosphate-uptake were measured for five experimental communities, two coral and three algal, for a total of 24 experiments. Uptake rate constants (S) ranged from 0.82 to 6.9 m day-1 over water velocities of 10 to 50 cm s -1. Uptake was proportional to water velocity and was close to mass-transfer limitation. Phosphate-loading rates, between 0.22 and 1.9 mmol m-2 day-1, were typical of natural loading. Excretion rates increased over time and ranged from 0 to 2.1 mmol m-2 day-1. S was not significantly different under steady versus oscillatory flow. The rate of phosphate-uptake may be enhanced by nitrogen-loading.