Noeffects of ambient UV radiation detected in periphyton and grazers

Abstract

The vulnerability of periphyton and grazers to current and future levels of ultraviolet radiation (UV) has important ramifications for energy flow in shallow waters. We reduced ambient UV levels in a Tennessee stream with UV‐opaque Plexiglas suspended over the stream and compared periphyton under these Plexiglas filters to periphyton under UV‐transparent polyvinylidene film. The experiments were performed three times, from autumn 1993 to summer 1994. The last experiment included a treatment with reduced snail densities, so potential interactions between grazing and UV could be identified. Periphyton biomass and photosynthesis were not significantly affected by reduced UV in any of the three experiments, indicating ambient UV effects were minor, at most. Grazing by snails (Elimia clavaeformis) tightly controlled periphyton biomass and primary production in all three experiments. Snail densities were not significantly affected by ambient UV, eliminating the possibility of a solar cascade of indirect effects. Snails may be less vulnerable to UV than are soft‐bodied grazers such as chironomids, and periphyton in southern U.S. streams may be adapted to naturally high levels of UV. The results of this study clearly imply that previous reports of UV impacts on periphyton and grazers cannot be generalized.

Grazing and UV radiation effects on an Antarctic intertidal microalgal assemblage: a long-term field study

“…These findings are in agreement with previous studies on benthic diatoms from marine (e.g., Hillebrand et al 2000), and freshwater (Steinman 1996;Hill et al 1997), habitats. In our study, the absence of grazers generally favoured the abundance of the diatom genus Cocconeis.…”

“…Thus, any UV effects on benthic diatoms should most likely be found here (particularly in the intertidal). However, the lack of UV effects found on biomass and abundance of benthic Antarctic diatoms confirmed former studies at different geographical sites (e.g., Hill et al 1997). Earlier field-studies on UV effects on benthic microalgae have mainly focussed on soft bottom communities where benthic diatoms seem to be very tolerant to UV-B radiation (Peletier 1996; and references therein).…”

“…However, no grazer -UV interactions were found in our study for the four sampling occasions as also observed by Hill et al (1997). No direct affect of UV radiation on the grazers occurring in the sampling area were detected.…”

Effects of UV Radiation on Wetland Periphyton: Algae, Bacteria, and Extracellular Polysaccharides

“…5 DISCUSSION Several investigations of the effects of UV radiation by exclusion of ambient UV observed reduced chl a accrual within +UV treatments in lakes Leavit 1996, Francoeur andLowe 1998) and artificial streams (Bothwell et al 1994, Hodoki 2005. In contrast, other studies conducted in lakes (Higley et al 2001, Watkins et al 2001), a wetland (Kahn and Wetzel 1999), and a stream (Hill et al 1997) found no significant differences in periphytic algal biomass between fill ambient sunlight (+UV) and PAR-only (-UV) treatments. In the present study, algal biomass appeared to be unaffected by W exposure.…”

“…Prior studies have observed reductions in algal photosynthesis and biomass accumulation in freshwater periphyton under full ambient light (+UV) as compared to -UV treatments (e.g., Vinebrooke and Leavitt 1996), whereas other studies have observed no affect of UV radiation (Hill et al 1997, Hodoki 2005. Shifts in algal species composition have also been observed in longer-term studies, with sensitivity to UV varying by taxon (Bothwell et al 1993, Vinebrooke and Leavitt 1996, Francoeur and Lowe 1998, Higley et al 2001).…”