Solar ultraviolet-B radiation effects on growth and pigment composition of the intertidal alga Ulva expansa (Setch.) S.&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 rates 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 carotenoids per unit weight were higher after growth under UV-B-transparent screens than under UV-B-opaque screens. These results indicate that chlorophyll a and carotenoid synthesis was not inhibited by UV-B. Nitrogen supplementation (10 mu M NaNO3) enhanced the growth rates of both UV-B-exposed and -unexposed segments; however this supplementation did not affect the sensitivity of the algal segments to UV-B. Growth rates of Ulva segments grown attached to frames on the mudflats were similar to those measured in the outdoor tanks, supporting the assumption that the effects of UV-B measured in outdoor tanks used in this and other studies are relevant to natural populations. (C) 1998 Elsevier Science B.V.