Zooplankton
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)
