SOLAR ULTRAVIOLET-B RADIATION EFFECTS ON GROWTH AND PIGMENT COMPOSITION OF THE INTERTIDAL ALGA ULVA-EXPANSA (SETCH.) S.AND-G. (CHLOROPHYTA)

Segments of Ulva expansa (Setch.) S. & G. (Chlorophyta) were grown in outdoor tanks under UV-B-transparent or UV-B-opaque screens. Growth ra tes of the segments were measured by changes in surface area. Amounts of chlorophyll a, carotenoids, and UV-absorbing compounds per segment did not vary systematically with treatments, but chlorophyll a and car otenoids per unit weight were higher after growth under UV-B-transpare nt screens than under UV-B-opaque screens. These results indicate that chlorophyll a and carotenoid synthesis was not inhibited by UV-B. Nit rogen supplementation (10 mu M NaNO3) enhanced the growth rates of bot h UV-B-exposed and -unexposed segments; however this supplementation d id not affect the sensitivity of the algal segments to UV-B. Growth ra tes of Ulva segments grown attached to frames on the mudflats were sim ilar to those measured in the outdoor tanks, supporting the assumption that the effects of UV-B measured in outdoor tanks used in this and o ther studies are relevant to natural populations. (C) 1998 Elsevier Sc ience B.V.