| The nutrient availability, growth and other related characteristics of three red tide algae, Skeletonema costatum, a diatom, Prorocentrum minimum and Alexandrium tamarense, two dinoflagellates, were investi- gated. Alexandrium tamarense showed the highest specific growth rate at low nitrate level. Maintenance of continues low level nitrate with sufficient supply of phosphate, namely low N:P ratio, may facilitate the growth of Alexandrium tamarense. When cultures at low level nitrate were supplemented with nitrate in middle exponential growth phase or with nitrate and phosphate in stationary growth phase, the cell yield was markedly enhanced, it was 8-9 times of the control culture without any nitrate and phosphate supplement,the toxin yield was also increased by over 8 times. However, supplementation with nitrate and phosphate in middle exponential growth phase or with nitrate in stationary growth phase increased the cell yield by no more than 2 times. The cells of Alexandrium tamarense grown under high level nitrate showed the lowest values of chlorophyll a-specific light-saturated photosynthetic rate (Pmchl a), dark respiration rate (Rdchl a) and apparent photosynthetic efficiency ((chl a). The values of Pmchl a, and (chl a showed increasing trend with the increase of phosphate concentration in culuture medium. For the cells of Prorocentrum minimum, the higher chlorophyll a-specific light-saturated photosynthetic rate(Pmchl a)and higher light-saturated point (Ik) at which photosynthesis is initially were observed when the nutrient levels were high. For the cells of Skeletonema costatum, the cells grown at low nutrient levels were active and their chlorophyll a-specific light-saturated photosynthetic rate (Pmchl a) and apparent photosynthetic efficiency ((chl a) changed not markedly with the change of nutrient levels.The half-saturation constants Ks for the uptake of nitrate and phosphate by Skeletonema costatum, Prorocentrum minimum and Alexandrium tamarense were 0.40, 5.18, 30.9?M and 0.65, 1.66, 2.70?M respectively. For growth dynamics the values Ks associated with nitrate and phosphate were 7.61, 20.52, 35.55?M and 0.21, 1.39, 1.52?M respectively. Skeletonema costatum gave the lowest Ks value but Alexandrium tamarense showed the highest one, while the specific growth rate exhibited contrary results. Nutrient uptake affinity and specific growth rates of both Alexandrium tamarense and Prorocentrum minimum were lower than those of diatom Skeletonema costatum. In Silicate-rich cultures Skeletonema costatum was a good competitor, and the other two dinoflagellates were growth-restricted. This result was not due to N or P limitation. In the medium with 10?M SiO32- the two dinoflagellate could grow at a certain growth rate. Under nitrate-limited conditions the growth of Skeletonema costatum increased significantly due to its small cell size and lower demand for nitrogen, while the two dinoflagellate with large cell size increased slowly and resulted very low cell yields. Under phosphate-limited conditions, the propagation of Skeletonema costatum was severely restricted and the cell density apparently decreased. The restriction on dinofalgellates caused by phosphate limitation was not severely. In the medium with low silicate and high level phosphate, the growth of Skeletonema costatum decreased at later growth stage, while the cell numbers of Prorocentrum minimum increased continuously and finally it became dominant specie.The general effects of zinc limitation on algae are the reduction in carbonic anhydrase activity then carbonic anhydrase activity further influenced the uptake of inorganic carbon and affected the CO2 fixation which in turn resulted in the decrease of photosynthetic efficiency. The response to zinc limitation were different from various species. The results obtained in this study showed that Prorocentrum minimum was more sensitive to zinc limitation than Skeletonema costatum, however excessive zinc imposed much more restriction on the growth of Skeletonema costatum than tho...
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