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Introduction

Solar short-wavelength radiation has been shown to reach ecologically significant depths in many freshwater and marine ecosystems (USEPA, 1987; Smith et al., 1992; Scully and Lean, 1994; Häder, 1995a; Booth et al., 1997; Coohill et al., 1996). Drastic stratospheric ozone depletion over both the Antarctic and Arctic, as well as moderate decreases in total ozone column over high and mid-latitude waters, have been reported. There is strong evidence that these trends increase the amount of solar UV-B which penetrates within the euphotic zone, where phytoplankton productivity takes place. In addition, there is evidence that it alters the ratio of UV-B:UV-A:PAR radiation which may impair the delicate light-dependent responses of aquatic organisms, including photosynthesis, photoorientation, photoinhibition and photoprotection (Smith et al., 1992; Häder et al., 1995; Gerber et al., 1996; Jiménez et al., 1996; Häder, 1997a,b). Changes in the spectral composition exceeding those experienced during the evolution of exposed organisms may pose significant stress for the diverse aquatic ecosystems (IASC, 1995). Both UV-B and UV-A affect growth and productivity by a number of mechanisms involving several molecular targets within the exposed cells. While most organisms possess effective protective and repair mechanisms, excessive exposure to solar UV radiation may overload their capabilities.

    Significant changes of solar UV on aquatic ecosystems may result in decreased biomass productivity. The impact of this decrease would be reflected through all levels of the intricate food web, resulting in reduced food production for humans (Häder et al., 1995; Häder, 1997e; Häder and Worrest, 1997), reduced sink capacity for atmospheric carbon dioxide (Ducklow et al., 1995; Takahashi et al., 1995, 1997), as well as changes in species composition and ecosystem integrity. The role of oceanic carbon dioxide uptake in global warming is of high significance (Sarmiento and Le Quéré, 1996; Thomson, 1997). However, the potential impact of ozone depletion on atmospheric carbon dioxide, mediated through inhibition of marine primary production, is uncertain and a more rigorous and detailed analysis is urgently needed. Research has been intensified over the last few decades to evaluate UV-B related damage of aquatic ecosystems (Nolan and Amanatidis, 1995). Important reviews on various aspects of UV effects on aquatic ecosystems include: aquatic ecosystes in general (Häder 1997c; Häder and Worrest, 1997); the role of MAA‘s in marine organisms (Dunlap and Shick, 1998); phytoplankton (Cullen and Neale, 1997a,b; Häder, 1997a); microalgae (Franklin and Foster, 1997; Häder and Figueroa, 1997); corals and coral bleaching (Shick et al., 1996; Lesser, 1996); lake acidification and UV penetration (Williamson, 1995, 1996).


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