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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