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Phytoplankton concentrations depend not only on nutrient availability, light, temperature and UV stress but also strongly on the grazing losses due to zooplankton activity (Banse, 1995). The zooplankton communities in turn not only depend on phytoplankton availability but also on grazing pressure as well as solar UV and temperature. Even at current levels, solar UV-B radiation can be a limiting factor, and small increases in UV-B exposure could result in significant reductions in the size of the consumer community (Damkaer, 1982; Kouwenberg et al., in press a). However, variability in cloud cover, water quality, and vertical distribution and displacement within the water column can all have an impact on the magnitude of the UV-B effect. Also, related to temperature effects, the macrozooplankton biomass in the California Current decreased by 80% since 1951 due to climatic warming by more than 1.5°C in some places (Roemmich and McGowan, 1995). As in phytoplankton, also in zooplankton UV-B induced DNA damage and photoenzymatic DNA repair have been demonstrated (Malloy et al., 1997). In planktonic embryos of copepods photoreactivation of UV induced damage was found to be an efficient repair mechanism (Naganuma et al., 1997). However, UV severely affects survival, fecundity and sex ratio in several intertidal copepods while others remained largely unaffected (Chalker-Scott, 1995).

Tab. 4.1 Structure, absorption maximum and retention time (HPLC) of some common mycosporines (Karentz et al., 1991)

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