NUTRIENT-UPTAKE IN THE REEF-BUILDING CORAL ACROPORA-PALMATA AT NATURAL ENVIRONMENTAL CONCENTRATIONS

Mean net rates of nitrate uptake exceeded that of ammonium uptake by a factor of 2. Nitrate uptake was dependent on substrate concentration, with a linear response over the range of ambient seawater concentrations encountered. Rate of ammonium uptake was apparently independent of substrate concentration and the rate of uptake of each ion was independent of the concentration of the others. A diurnal rhythm was noted in nitrate uptake rates. Results support previous studies which demonstrate the capability for dual uptake of both nitrate and ammonium by zooxanthellae, but suggest that under natural conditions nitrate rather than ammonium provides the primary external source of dissolved inorganic nitrogen in this species. -from Author