마산만에서 분리한 유독 와편모조류 Alexandrium tamarense와 Alexandrium catenella의 DON 이용성

Abstract

DON utilization of toxic dinoflagellate Alexandrium tamarense and Alexandrium catenella isolated from Masan Bay

Ji-A Park

Department of Oceanography, The Graduate School, Pukyong National University

Abstract

The coastal areas of Korea are being developed into aquaculture industries. However, the problem of paralytic shellfish poisoning (PSP) induced by toxic dinoflagellates in spring is almost an annual event. This causes the aquaculture industry and public health to be severely affected. Moreover, the cell density of PSP-causing organisms and the areas of PSP occurrence are gradually increasing in the southern sea of Korea. Thus, the purpose of this study was to evaluate the physiological characteristics and dominant strategy of Alexandrium tamarense and Alexandrium catenella, which are major PSP-causing dinoflagellates under DIN conditions through field observations in the Masan Bay and laboratory experiments. In the field observations, Alexandrium spp. were observed from April to July, and they especially accounted for about 60% of the dinoflagellates observed between May and June. During these periods, the N:P ratio was indicated as less than 16 which means that nitrogen is the limiting factor for the growth of phytoplankton. However, dissolved organic nitrogen (DON) accounted for approximately 70% of dissolved total nitrogen (DTN). Thus DON may be playing the role of an important nutrient for species spreading and the survival strategy of the two species under DIN-limited conditions. To test my hypothesis of DON utilization by A. tamarense and A. catenella, this study examined the two speceis in the laboratory. First, the effects of temperature, salinity and irradiance on the growth of the two species were investigated as the preliminary experiment. Temperature and salinity conditions for maximum growth rate were indicated as follows: temperature 15℃ and salinity 30 psu in A. tamarense, and temperature 25℃ and salinity 30 psu in A. catenella. Irradiance conditions were determined as 300 μmol m-2 s-1 in both species. These conditions were used to set up the later experiments. In the utilization experiment of DON, A. tamarense and A. catenella were able to grow using DON(i.e. urea and amino acids) as well as DIN(i.e. nitrate and ammonium). Compared to the growth rates of the two speceis with nitrate, those of the two speceis with urea and amino acids corresponded to 90% and 60%, respectively. Thus, these species might be able to grow using DON under DIN-limited conditions in spring in the Masan Bay. In the growth kinetics experiment of nitrogen compounds(nitrate, ammonium and urea) under DIN-limited conditions, Ks (half saturation constant; affinity index) values were 2.44 μM, 1.07 μM and 2.93 μM for A. tamarense, and 3.78 μM, 0.72 μM and 1.67 μM for A. catenella. However A. tamarense and A. catenella might be at a disadvantageous position because the Ks values of nitrate and ammonium calculated from the growth kinetics experiment of these species were more similar than those of diatoms. However, the high availability of DON might be able to overcome the disadvantageous physiological characteristics of nitrate. Therefore, the utilization of DON by A. tamarense and A. catenella may have led to an important survival strategy and dominance strategy in DIN-limited conditions such as those in the Masan Bay.