THE EFFECT OF UV-B RADIATION ON PHOTOSYNTHESIS AND RESPIRATION OF PHYTOPLANKTON, BENTHIC MACROALGAE AND SEAGRASSES

Several species of marine benthic algae, four species of phytoplankton and two species of seagrass have been subjected to ultraviolet B irra diation for varying lengths of time and the effects on respiration, ph otosynthesis and fluorescence rise kinetics studied. No effect on resp iration was found. Photosynthesis was inhibited to a variable degree i n all groups of plants after irradiation over periods of up to 1 h and variable fluorescence was also inhibited in a similar way. The most s ensitive plants were phytoplankton and deep-water benthic algae. Inter tidal benthic algae were the least sensitive to UV-B irradiation and t his may be related to adaptation, through the accumulation of UV-B scr eening compounds, to high light/high UV-B levels. Inhibition of variab le fluorescence (F(v)) of the fluorescence rise curve was a fast and s ensitive indicator of UV-B damage. Two plants studied, a brown alga an d a seagrass, showed very poor recovery of F(v) over a period of 32 h.