Uptake And Utilization Characteristics Of Harmful Algal Bloom Species For Dissolved Free Amino Acids

In recent years, dissolved organic nitrogen (DON) has been the fast-growing nitrogen source in the coastal waters around the world. Increasing studies showed that DON was closely related to the occurrences of harmful algal blooms (HABs), for which could promote the proliferation of some red tide organisms. In order to evaluate the uptake and utilization characteristics of some representative HAB species for amino acids, and reveal the potential effects of the rise of DON concentration in the coastal waters on phytoplankton succession and HABs formation, this paper investigated the spatial and temporal variation characteristics of DON and phytoplankton community succession in Daya Bay of Guangdong province. The availability of amino acids for the representative harmful algae Prorocentrum donghaiense, Phaeocystis globosa, Skeletonema costatum and Karenia mikimotoi were investigated in laboratory. Uptake kinetics and light system response characteristics of P. donghaiense and P. globosa for amino acid were examined, and the effects of inorganic nutrients, irradiance and temperature on the utilization of P. donghaiense and P. globosa for amino acid were also studied. The main results were as follows:Population dynamics of Gymnodinium spp. and environmental factors in aquaculture areas of Daya Bay were investigated from January to December in 2008. The dominant Gymnodinium species was Gymnodinium sp., a relatively small species with the diameter of 16-22μm, and Karenia mikimotoi, Gymnodnium catenatum and Akashiwo sanguinea were found at low density. Obvious seasonal and spatial distribution characteristics were existed in cell density of Gymnodnium group. The highest density of 903 cells·mL-1 was observed in May, while the lowest in autumn and winter. And the population density of Gymnodnium group was higher in aquaculture areas and coastal areas than the open sea. Correlation analysis showed that temperature, COD (chemical oxygen demand), DON (dissolved organic nitrogen) and urea played key roles in regulating the density of Gymnodinium group. The optimal temperature range for Gymnodnium group were 25～30℃, while DON and urea were 156.38～187μgN～L-1 and 1.74～4.06μgN～L-1 respectively. Our findings suggested when the temperature was suitable, organic nitrogen such as urea may play a trigger in the formation of Gymnodinium blooms.The growth characteristics, uptake kinetics and light system response characteristics of three representative harmful algae P. donghaiense, P. globosa and K. mikimotoi were studied in batch culture with free amino acid as single nitrogen source, and the common phytoplankton species S. costatum was used as control. The results showed that the responses to free amino acid were significantly different among phytoplankton species. P. donghaiense and P. globosa could utilize multiple free amino acids for growth, while K. mikimotoi and S. costatum could not grow with free amino acids as sole nitrogen source. The specific growth rate of P. donghaiense and P. globosa were significantly different with different amino acids.50μmol amino acid could maintain high level of Fv/Fm in the late stage of nitrogen-limited harmful algae. The maximum alanine uptake rate of P. donghaiense and P. globosa were 0.47 pmol·cell-1·h－1 and0.11 pmol·cell-1·h-1 respectively, while half-saturation constants were 3.32 pmol and0.41 pmol. Because the responses to free amino acids were significantly different among phytoplankton species, the composition of phytoplankton community may change and the species which could utilize amino acids would have advantages.The amino acid oxidase activity of P. donghaiense and P. globosa were influenced by nitrogen source, irradiance, temperature and other environmental factors. The temperature is the key factor regulating the amino acid oxidase activity of P. donghaiense and P. globosa, while too high or low temperature could inhibit amino acid oxidase activity. The highest amino acids oxidase activities of P. donghaiense and P. globosa were obtained under the highest irradiance (100μmol·m-2·s-1), and the activities decreased at the low irradiance.