| In recent years, the impacts of algal blooms (red tides)dominated by dinoflagellates on marine ecosystem and fishery production have been incrased in coastal waters of the East China Sea. Very low levels of inorganic phosphate were confirmed after a large-scaled diatombloom. However, following the diatom blooms, the dinoflagelletes'blooms were able to burst and lasting for a long time still.Therefore, the blooms caused by the algae "diatoms-dinoflagellates-diatoms"alternatively occurred in different seasons, indicating phosphorus pools existed in dinoflagellate cells. Furthermore, the common harmful blooms-forming dinoflagellates Karenia mikimotoi and Prorocentrum donghaiense usually showed higher competitiveness than other algae. In this paper, the physiological activities and cellular phosphorus pool characteristics of them were studied under different temperatures and phosphorus concentrations to evaluate the aging of common algal blooms.In addition, the field researches were carried out to investigate the effects of dinoflagellate blooms on diversity of plankton community. The main findings are as follows:The effects of phosphate concentrations and temperature levels on growth and phosphate pool charactors of K. mikimotoi and P.donghaiense were studied to simulate the low phosphate levels and fluctuant temperatures of surface seawater. The results showed thatphosphate deficiency inhibited the growth of both dinoflagellates.However, the cells of K. mikimotoi still increased and those of P.donghaiense could keep stable (1.88×104?3.19×104 cells mL-1) for a month when cultured at a very low phosphate level (0.28 ?mol·L-1). On the other hand, the different rotios of extracellular phosphorus pools to intracellular ones were identified between the two dinoflagellates. It indicated that different phosphate storage mechanisms existed between K.mikimotoi and P. donghaiense.In the case of sufficient phosphorus, K. mikimotoi quickly assimilated the phosphorus from the water during a certain period of time.There were no significant difference in the maximum uptake rate (?max)and half-saturated absorption constant (Ks) of inorganic phosphorus when K. mikimotoi were cultured at 16, 20 and 24 0C. The ?max and Ks of K.mikimotoi cultured at 28 ? significantly (P<0.05) higher than those cultured at above mentioned three temperature gradients, were 34.722 finol·cell-1·h-1 and 1.354 ?mol·L-1, respectively. The phosphorus absorption rate inversely proportional to temperatures ranged 16 to 28 ?.The phosphorus uptake kinetics of K. mikimotoi was determined by establishing a single-stage kinetic model of phosphorus uptake and measuring the total phosphorus concentration in cells. It was found that the cell densities of K. mikimotoi increased with increased inorganic phosphorus levels. Furthermore, the ones cultured at high-phosphorus level began to significant (P<0.05) higher than those cultures at mediem- and low-phosphorus levels from the 12th day.Conversely, the cell volumes of those cultured at the low-phosphorus level began significantly (P<0.05) bigger than those cultured at high- and medium-phosphorus levels from the 6th day.Field studies carried out in algal blooms waters of Wenzhou in Zhejiang Province in May and June of 2016, proved the significant effects of the algal bloomon the plankton communitystructure. The blooms caused by P. donghaiense and dominated by Akashiwo sanguine occurred between the 9th to 20th in May and 17th to 18th in June of 2016,respectively. The average abundances of phytoplankton in zone of algal blooms were higher than those outside. However, the results of zooplankton were contrary to phytoplankton species. The species diversity and abundance index of the phytoplankton in the algal bloom area were significantly higher than those in the non-algalbloom but the diversity and evenness index were lower than those in the non-algal bloom area in May. The diversity index of zooplankton in algal bloom and non-algal bloom area was insignificant in June.The growth characteristics of dinoflagellates combined the inorganic phosphorus uptake indicated that cell phosphorus pools existed in both dinoflagellates, and supporting them to grow continuely under low phosphorus level. K. mikimotoihave higher competitive advantage compared with P. donghaiense under lowphosphorus condition. The results indicated that inorganic phosphorus concentration and intracellular phosphorus pool had an important effect on the process of algal blooms.The diversity of plankton changed much during the occurrence and vanishiment process of algal blooms.Further studies were needed to revealthe relationship between the characteristics of phosphorus pools in dinoflagellate cells and the aging of algal blooms. |
PDF Full Text Request