Algae. 2003; 18(1): 13-20.
UV-B Effects on Growth and Nitrate Dynamics in Antarctic Marine Diatoms Chaetoceros neogracile and Stellarima microtrias
Jae-Shin Kang, Sung-Ho Kang, Youn-Ho Lee, Jung-Hee Shim, Sang-Hoon Lee
Polar Sciences Laboratory, Korea
Ocean Research, Development Institute
Two isolated Antarctic marine diatoms, Chaetoceros neogracile VanLandingham and Stellarima microtrias (Ehrenberg) Hasle and Sims were examined to show changes of growth and uptake rate of nitrate due to UV-B irradiance. Chlorophyll (chl) a concentration was regared as the growth index of diatom. The diatoms were treated with UV-B radiation and cultured for 4 days under cool-white fluorescent light without UV-B radiation. Two levels of UV-B exposures were applies: 1 and 6 W m-2. Durations of UV-B treatment were 20, 40 and 60 minutes under 6 W m-2 and 1, 2, 3, 4 and 5 hrs under 1 W m-2. The control groups were cultured at the same time without UV-B radiation. The growth rates of two diatoms decreased under 1 and 6 W m-2 UV-B irradiances than that of control group. After 4 days, chl a concentrations of C. neogracile were increased more than 4 times from 133 ㎍?l-1 to 632 ㎍?l-1 in control group. However, the concentration of experimental groups under 1 W m-2 UV-B were only increased from 139 ㎍?l-1 to 421 ㎍?l-1 during one hour and the chl a concentrations were decreased from 144 ㎍?l-1 to 108 ㎍?l-1 during five hour. Growth of diatom dramatically more decreased under 6 W m-2 UV-B than 1 W m-2 UV-B. The chl a concentration of experimental groups under 6 W m-2 UV-B for one hour was only increased from 111 ㎍?l-1 to 122 ㎍?l-1. In the case of S. microtrias showed also similar pattern to C. neogracile by UV-B radiation. The uptake rates of nitrate by the two strains were decreased abruptly under 6 W m-2 UV-B irradiances. When two strains were treated under 1 and 6 W m-2 UV-B during one hour, the strains were only continued growth and uptake of nitrate under 1 W m-2 UV-B. This experimental evidence shows that exposure to UV-B radiation especially to high irradiance of UV-B decreases diatom survival and causes lower decrease of nutrient concentrations by microalgae in Antarctic water. Furthermore, evidence suggests that microalgal communities confined to near-surface waters in Antarctica will be harmed by increased UV-B radiation, thereby altering the dynamics of Antarctic marine ecosystems.
Keywords : Antarctic diatoms, Chaetoceros neogracile, chlorophyll a, growth and nitrate dynamics, Stellarima microtrias, UV-B