EFFECTS OF UV-B IRRADIATION ON GROWTH AND SURVIVAL OF ANTARCTIC MARINE DIATOMS

Growth rate, survival, and stimulation of the production of UV-B (280 to 320 nm) absorbing compounds were investigated in cultures of five c ommonly occurring Antarctic marine diatoms exposed to a range of UV-B irradiances. Experimental UV-B exposures ranged from 20 to 650% of the measured peak surface irradiance at an Antarctic coastal site (0.533 J m(-2) s(-1)). The five diatom spe cies (Nitzschia lecointei, Probosc ia alata, P. inermis, Thalassiosira tumida and Stellarima microtrias) appear capable of surviving two to four times this irradiance. In cont rast to Phaeocystis cf. pouchetii, another major component of the Anta rctic phytoplankton, the concentrations of pigments with discrete UV a bsorption peaks in diatoms were low and did not change significantly u nder increasing UV-B irradiance. Absorbance of UV-B by cells from whic h pigments had been extracted commonly greatly exceeded that of the pi gments themselves. Most of this ab sorbance was due to oxidisable cell contents, with the frustule providing the remainder. Survival of diat oms did not correlate with absorption by either pigments, frustules or oxidisable cell contents, indicating that their survival under elevat ed UV-B irradiances results from processes other than screening mechan isms.