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The effects of UVB radiation on the growth of macroalgal thalli were evaluated using tetrasporophytic fronds of the Rhodophytes Gigartina skottsbergii, Sarcothalia crispata and Mazzaella laminarioides. The tetrasporophytic fronds were collected from nature and the tetrasporophyte sporelings grown in a temperature regulated chamber at 8 ± 2 • C with a 12L:12D (Light: Dark) photoperiod, Photosynthetically Active Radiation (PAR) of 55 μmol photons m −2 s −1 and seawater enriched with 20 mL L −1 of Provasoli medium. We exposed the thalli of these macroalgae to PAR (55 μmol photons m −2 s −1 ) and three treatments using a combination of PAR with three different levels of UVB radiation (0.10, 0.15 and 0.23 W m −2 for G. skottsbergii and S. crispata and 0.02, 0.05 and 0.10 W m −2 for M. laminarioides) during a period of 71 days. Growth of thalli was quantified by measuring their length using digitized photographs of samples.Important differences were detected in the growth of individuals cultured under the effects of UVB radiation, when compared to the control (i.e. plants exposed to PAR only). In the case of G. skottsbergii and S. crispata higher levels of UVB radiation resulted in slower growth of thalli. In nearly all measurements for the first two species, UVB radiation levels of 0.1 W m −2 induced differences in thallus growth, while for M. laminarioides levels of UVB radiation of 0.1 W m −2 were effective only after a prolonged period of exposure.Differential effects of UVB radiation on G. skottsbergii, S. crispata and M. laminarioides could interfere with the natural populations of these economically important macroalgal species in southern Chile, where they occur under the annual influence of the Antarctic Ozone Hole and the general thinning of the ozone layer.

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Treatment of Gnaphalium vira-vira plants with UV-B radiation caused changes in plant growth and in plant chemistry. The leaf surface contained two O-methylated flavones, araneol and 7-O-methylaraneol. HPLC analysis showed that 20 days of UV-B radiation increased the synthesis of 7-O-methylaraneol at the expense of araneol. Spectrophotometric analysis of the photosynthetic pigments showed that UV-B radiation also increases the pigment content in treated plants. Another U V alteration is epidermal hair damage, as observed in SEM pictures of treated leaves. This combination of physiological and phytochemical effects may be interpreted as a plant response to UV-B stress