INHIBITION OF GROWTH OF ULVA-EXPANSA (CHLOROPHYTA) BY ULTRAVIOLET-B RADIATION

We examined the effect of ultraviolet-B radiation (UV-B, 290-320 nm) o n the growth rate of the intertidal marine alga Ulva expansa (Setch.) S. & G. (Chlorophyta). Segments of thallus collected from a natural po pulation were grown in outdoor seawater tanks. Combinations of UV-B-op aque screens, UV-B-transparent screens, and W-B lamps were used to inv estigate the effects of solar UV-B and solar plus supplemental UV-B on the growth of these segments. Growth was measured by changes in segme nt surface area, damp weight, and dry weight. Growth rates of segments were inhibited under both solar W-B and solar plus supplemental W-B t reatments. Growth rates were also inhibited by high levels of photosyn thetically active radiation, independent of UV-B fluence. These result s indicate that increases in UV-B resulting from further ozone depleti on will have a negative impact on the growth of this alga.