We examined the effect of ultraviolet‐B radiation (UV‐B, 290–320 nm) on the growth rate of the intertidal marine alga Ulva expansa (Setch.) S. & G. (Chlorophyta). Segments of thallus collected from a natural population were grown in outdoor seawater tanks. Combinations of UV‐B‐opaque screens, UV‐B‐transparent screens, and UV‐B lamps were used to investigate the effects of solar UV‐B and solar plus supplemental UV‐B on the growth of these segments. Growth was measured by changes in segment surface area, damp weight, and dry weight. Growth rates of segments were inhibited under both solar UV‐B and solar plus supplemental UV‐B treatments. Growth rates were also inhibited by high levels of photosynthetically active radiation, independent of UV‐B fluence. These results indicate that increases in UV‐B resulting from further ozone depletion will have a negative impact on the growth of this alga.
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Grobe et al. (1994) studied this question.