Abstract

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39° S), accompanied by evaluation of the impact of ultraviolet radiation (UVR) on marine macroalgae of this site. UVR conditions showed a strong seasonal variation, which was less pronounced toward longer wavelengths. Daily maximum dose rates (clear days) averaged in winter-summer: UV-B (290-315 nm) 0.30-2.1, UV-B (290-320 nm) 0.70-3.7, UV-A (315-400 nm) 20.6-62.1, UV-A (320-400 nm) 20.2-60.5 W m -2, and photosynthetically active radiation (PAR) 969-2423 μmol m -2 s -1. The corresponding daily doses (all the days) ranged: UV-B (290-315 nm) 2.6-40.7, UV-B (290-320 nm) 6.7-78.5, UV-A (315-400 nm) 228-1539, UV-A (320-400 nm) 224-1501, and PAR 2008-13308 kJ m -2 d -1. Taking into consideration action spectra of a biological interest, the risk of UV exposure could be up to 37 times higher in summer than in winter. The photosynthetic activity (as maximum quantum yield of chlorophyll fluorescence, F v/F m) of the brown alga Lessonia nigrescens from the infralittoral zone was markedly more sensitive to UVR than of the green alga Enteromorpha intestinalis from the upper midlittoral, and the UV-B wave band increased markedly photoinhibition. In L. nigrescens, maximal photoinhibition (40%) took place at weighted (the action spectrum for photoinhibition of photosynthesis) UVR doses of 800 kJ m -2, irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 kJ m -2). In winter, when this alga was at its most sensitive, the weighted UV dose causing 35-40% photoinhibition was around 200 kJ m -2. In E. intestinalis, weighted doses of 800 kJ m -2 resulted in low photoinhibition (<10 %) and no clear seasonal patterns could be inferred. These results confirm that midday summer levels of UV-B and their daily doses in southern Chile are high enough to produce stress to intertidal macroalgae. © 2006 American Society for Photobiology.