A five-year study of solar ultraviolet radiation in southern Chile (39° S):: Potential impact on physiology of coastal marine algae?

This study reports 5 years of (1998-2003) data on continuous solar-irradiation measurements from a scanning spectroradiometer (SUV-100) in Valdivia, Chile (39 degrees 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)) 20.2-60.5 W m(-2), and photosynthetically active radiation (PAR) 969-2423 mu mol 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 lyield 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 2 doses of 800 kJ m-, irrespective of the season (corresponding midsummer daily dose in Valdivia is 480 W 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.