Abstract
Epilithic communities from brackish coastal water of the east coast of Sweden were studied in order to reveal their responses to different levels of UV-B radiation. The experiment was conducted for seven days in an indoor microcosm system. The epilithic communities were exposed daily to different doses of UV-B radiation: 1, 3, 5 and 7 hours, respectively. The intensity of the UV-B radiation used was similar to that in natural environments. After seven days clear shifts both in species composition and community structure were observed. All species of diatoms showed negative correlation with enhanced levels of UV-B. On the other hand, abundance of cyanobacteria was positively correlated with enhanced levels of UV-B (Calothrix aeruginea, R=0.49;Oscillatoria amphibia, R=0.93; Pseudanabaena mucicola, R=0.26). Communities dominated by diatoms and green algae at the initial stage of the experiment did show a drastic decrease in diatom abundance under UV-B stress and finally became dominated by cyanobacteria. Among green algae the abundance of Cladophora sericea correlated positively (R=0.33) with enhanced exposure to UV-B, while Monoraphidium-species exhibited negative correlation to UV-B. Otherwise, no significant correlation between other green algae species identified and UV-B stress could be detected. We conclude that UV-B radiation, even at lower levels, is capable to induce severe changes to marine epilithic communities. The trends revealed in the present study predict a shift from communities dominated by diatoms and green algae to those dominated by cyanobacteria.
Highlights
A great environmental problem recognised during recent years is ozone depletion and a following increase of penetrating ultraviolet-B radiation (UVB, 280-315 nm)
It has been well documented that UV-B radiation is capable of causing considerable damage to living organisms, both in aquatic and terrestrial habitats (e.g. Nolan and Amanatidis, 1995; Lean, 1998)
All macroinvertebrates were carefully removed from the stones collected, after which the stones were placed in a 40 l glass enclosure with artificial flow and aeration
Summary
A great environmental problem recognised during recent years is ozone depletion and a following increase of penetrating ultraviolet-B radiation (UVB, 280-315 nm). It has been well documented that UV-B radiation is capable of causing considerable damage to living organisms, both in aquatic and terrestrial habitats Ty of UV-B to produce free radicals of great oxidative power is well known (Halliwell and Gutteridge, 1989), and the effects induced by enhanced exposure to UV-B at the cellular level are complex and often of considerable damage to living organisms (for review see Hessen et al, 1997). Various species of algae differ in their sensitivity to UV-B radiation Taking this fact into account, changes in species composition depending on the UV-B doses can be expected (Cullen and Neale, 1994; Villafane et al, 1995; Helbling et al, 1996; Wängberg et al, 1996). Successions at the level of primary producers would undoubtedly affect higher trophic levels and cause changes in the entire aquatic ecosystem
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