The potential feedback by intracellular nitrogen pools on maximum N uptake (NH4+) rate were determined for Gracilaria tenuistipitata var. liui and Ulva pertusa. The results of correlation matrix analyzing showed that the surge uptake of ammonium seemed related to rapid changes in small intracellular pools of inorganic nitrogen or small peptide and amino acids rather than to changes in TN content of the macroalgae. The assimilation rates of nitrogen of U. pertusa and G. tenuistipitata increased slowly during N starvation and were mainly regulated by amino acids and some incorporation of amino acids into macromolecules. From ecological point of view, the fast-growing and uptaking nutrient U. pertusa is more suitable to improve water quality in integrated shrimp culture ponds in which extal nutrient supplies are usually high and constant during the culture period, while G. tenuistipitata var. liui is more suitable to be polycultured in a waters with intermittence supply of nutrients.