Abstract:In order to evaluate the growth of A lexandrium tamarense, a toxic harmful algal bloom species, under nitrate and phosphate limitation, five test groups of both N and P limitation （N： 500-10 μg L-1, P：74-1.5 μg L-1, N：P=15：1） and nine test groups of only N or P limitation （N：500 μg· L^-1, P：74-0.74 μg L^-1 and P：74 μg L-1, N: 500-5 μg L-1 ） were set under laboratory conditions. Though cells ofA. tamarense multiplied exponentially just in the second day after inoculation in most test groups, the growth was obviously inhibited when both N and P limited simultaneously, and the cell densities did not show significant increase under N and P concentrations below 100 txg L-1 N and 15 txg L-1 P. However, cells grew significantly better in test groups of single nutrient element limitation than those under both N and P depletion. Furthermore, the growth of A. tamarense was affected less by moderate N or P limitation. The results suggested that the high ability of A. tamarense to adapt single nutrient limitation allows this harmful species to maintain constant growth rate and cell density in natural sea water, in which single nutrient limitation usually occurs, and thus helps shellfishes, feeding on A. tamarense, to accumulate paralytic shellfish poisoning （PSP）.