The effect of artificial ultraviolet (UV) and natural solar radiation on photosynthesis, res-. piration and growth was investigated in 14 red, green and brown macroalgal species on Spitsbergen. (Norway) during summer 1998. In June, maximum mean solar radiation at sea level was 120 W m-2 of. visible (370 to 695 nm) and 15 W m-' of UV radiation (300 to 370 nm), and decreased gradually until the. end of the summer.