AbstractIn specimens of the hermatypic coral speciesFungia scutariaandMontipora verrucosaand in the algaUlva lactuca, nitrate uptake was measured in light and dark with a flow‐through apparatus. The nitrate uptake was measurable in high‐nitrate bay water of Kaneohe Bay and also in low‐nitrate open ocean water. Nitrate consumption rates by the corals and the alga did not differ from light to dark.Neither the coral nor the alga showed measurable immediate nitrate uptake in open ocean water of low nitrate concentration when they had been held previously in the high‐nitrate bay water. In low‐nitrate open ocean water the uptake per unit time increases when the flow of the water increases.The uptake of nitrate by reef corals even from low concentrations indicates nonspecific nutrient sources for re