The uptake and release of dissolved phosphorus by reef corals1,2

Abstract

The fluxes of dissolved reactive, organic, and total phosphorus into and out of non‐feeding corals were measured by chemical and radiochemical techniques. A net uptake of reactive phosphorus from seawater by corals containing zooxanthellae was not, at typical ambient phosphorus levels, sufficient to offset simultaneous losses of organic P. Consequently, there was a net loss of total P. A coral without zooxanthellae was unable to remove net amounts of reactive P from solution even at levels above ambient. Reactive phosphorus uptake was light sensitive, was highly temperature dependent, showed characteristics of Michaelis‐Menten kinetics, and could be inhibited by arsenate. An active transport mechanism appears to be involved. The kinetics of net reactive phosphorus uptake were described by a Michaelis‐Menten equation modified to include a correction for an efflux of reactive P accompanying uptake. The mean half‐saturation (K) for uptake was 377 nM and the mean maximum rate of uptake (vmax) was 293 ng atoms P · mg Chl a−1 · h−1.Although the symbiotic corals tested cannot obtain all of the phosphorus they require by means of reactive phosphorus uptake at typical environmental concentrations, the ability of corals to obtain part of it in this manner, and the presence of mechanisms for efficient recycling of phosphorus within the symbiotic association, may help enable corals to flourish in waters low in phosphorus sources.