Effect Of Dissolved Inorganic Nutrients Composition On The Growth Of HAB Algae In East China Sea

In order to understand the mechanism of HAB outbrake to answer why one or several HAB species can overwhelm others and become dominant, both batch culture experiment in laboratory and mesocosm experiment in East China Sea are conducted to study the effects of dissolved inorganic nutrients composition on the growth of common HAB algae in East China Sea. And the experiments results show there exits a preliminary conclution that can explain the phenomenon that Prorocentrum donghaieme and Skeletonema costatum do not bloom at the same season.1. The effects of dissolved inorganic nutrients composition in the culture medium on the growth of HAB algae in East China SeaBased on the concentrations and structure of nutrients in East China Sea, a series of dissolved inorganic nutrients composition in laboratory is designed. Because Prorocentrum donghaiense, Skeletonema costatum and Chaetoceros curvisetus are common HAB algae in East China Sea, batch culture experiment is conducted to study the effects of changes of nutrients composition on them and the uptake of nutrients by them is also studied in this paper. The results showed that there exists a turning point where the initial nutrient concentration has a two-side effect on the algae growth, and that when the initial nutrient concentration is below the turning point, the growth process will be promoted with the increase of concentration, while on the contrary, the growth process will be suppressed. This result shows that the growth of HAB algae is not only determined by the dissolved inorganic nutrients concentrations, but also depends on the structure of nutrients.Further research shows that under high nutrients conditions, Skeletonema costatum grow better than Prorocentrum donghaiense, but under nutrients-limited conditions, Prorocentrum donghaiense grow better than Skeletonema costatum. 2.The uptake of dissolved inorganic nutrients by HAB algae in East China Sea In laboratory, the uptake of nutrients by HAB algae in East China Sea is studied. The order of the half-saturation constants for the uptake of phosphate by HAB algae was Skeletonema costatum> Chaetoceros curvisetus> Prorocentrum donghaiense. And the half-saturation constants for nitrate have the same order. The uptake rate of phosphate and nitrate by Skeletonema costatum is the highest. Those results shows that under low nutrients conditions, the growth of Skeletonema costatum would be limited more easily than others. In addition, further research shows that Skeletonema costatum can be limited by nitrate more easily than by phosphate.3. The effects of dissolved inorganic nutrients composition on the growth of phytoplankton in the mesocosm experimentIn the mesocosm experiment, the same conclusion is got as that in laboratory. The growth of HAB algae is not determined by the dissolved inorganic nutrients concentrations, but also depends on the structure of nutrients. When the N/P ratio is same in two mesocosms, phytoplankton would grow better in the higher concentrations of phosphate and nitrate. And under high nutrients conditions, Skeletonema costatum grew better than Prorocentrum donghaiense, but under nutrients-limited conditions, Prorocentrum donghaiense grew better than Skeletonema costatum.4. The suppose about the reason why Prorocentrum donghaiense and Skeletonema costatum not bloom at the same timeIn East China Sea, on one hand, the concentrations of nutrients in spring are lower than those in summer. On the other hand, Prorocentrum donghaiense blooms in spring and Skeletonema costatum blooms in summer. The above phenomenon isconsistent with the experiment results that have been discussed above. So a new supposition is put forward, that is, as the bloom of Prorocentrum donghaiense and Skeletonema costalum as concerned, nutrients concentration is a main control factor.