INFLUENCE OF SOLAR ULTRAVIOLET-RADIATION ON PHOTOSYNTHESIS AND MOTILITY OF MARINE-PHYTOPLANKTON

The effects of solar ultraviolet radiation (UV) on carbon uptake, oxyg en evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west co ast of Sweden (58 degrees 30'N, 11 degrees 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400-700 nm) 1670 mu mol m(-2) s (-1), ultraviolet-A radiation (UV-A, 320-400 nm) 35.9 W m(-2) and ultr aviolet-B radiation (UV-B, 280-320 nm) 1.7 W m(-2). UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greate r than 100-150 cm. Inhibition of carbon uptake by UV-A and UV-B in nat ural phytoplankton populations was greatest at 50 cm depth and the eff ects of UV-B were greater than those of UV-A. At depths greater than 5 0 cm there was almost no effect of ultraviolet radiation on carbon upt ake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagella te Prorocentrum minimum. Inhibition of oxygen evolution was greater af ter 4 h than 2 h but it was not possible to distinguish the negative e ffects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phyt oplankton to different light regimes before being exposed to natural s olar radiation is discussed.