Phosphorus Flux Across a Coral Reef

The concentrations of reactive and organic phosphorus were measured in seawater before and after the water had passed over the shallow windward coral reef flat north of Nuti Island, Eniwetok Atoll. These concentrations did not vary in proportion to the photosynthesis and respiration activities of the reef community. There were no detectable changes in either form of phosphorus between upstream and downstream ends of a transect across a relatively rich coral region, but on a transect across a predominantly algal—covered area there was a slight decrease in reactive phosphorus and a slight increase in organic phosphorus. There were no detectable diurnal variations in these patterns. This remarkable constancy suggests that the plants take up phosphorus at a nearly constant rate, regardless of the magnitude of photosynthetic activity.