80
M.T. Arts
optical-digital method to measure visible TAG and wax ester energy reserves in
calanoid copepods. They proposed that the distribution of storage lipids within the
body segments would be useful as a predictive and quantitative tool for monitoring and assessing the status of copepod populations with respect to their ability to
resist starvation or, alternatively, as an index of their recent feeding success.
Finally, in a study on the effects of acid stress on zooplankton communities,
Locke and Sprules (1993) stained zooplankton with a lipophilic dye (Sudan IV)
designed to accentuate the lipid stores in preserved samples (Bjorkman and
Shapiro, 1986). They demonstrated, using in situ enclosure experiments, that even
though some species of acid-tolerant species (e.g., Sida crystallina) persist in an
enclosure following acidification, their lipid energy reserves, as measured by their
lipid-ovary index scores, actually decreased. Interestingly, acid-tolerant species
that appeared to benefit from the reduced competition and increased food supplies
such as the cyclopoid copepods (e.g., Diacyclops thomasi) also contained increased levels of storage lipids (Locke and Sprules, 1993).
4.4.4. Fatty Acid Composition and Abundance
Examination of FA composition and abundance (FA profiles) in zooplankton in
relation to stress has not received the attention it deserves. Several examples in
algae (Mooney et aI., 1995; Sicko-Goad et al.. 1989) and periphyton (Napolitano
et aI., 1994) illustrate how FA profiles change as a function of stress. Because
zooplankton obtain their FAs from the diet, there is good reason to believe that
zooplankton FA profiles will also be affected by the presence of stressors. Because FAs are fundamental components of membranes, the effects of stressors on
FA composition and the subsequent health of zooplankton merit further attention.
4.5. Ultraviolet Radiation and Zooplankton Lipids
Significant reductions of stratospheric ozone have been observed over the past
decade, and there is concern that ultraviolet B (UV-B) radiation (300-320 nm)
reaching the earth's surface will also increase (Madronich, 1995). UV-B radiation
can penetrate to ecologically significant depths in natural waters, thus the observed increases in surface UV-B radiation have the potential to adversely affect
phytoplankton productivity, especially in shallow lakes, wetlands, and rivers.
There is new evidence to suggest that effects of UV-B radiation in freshwater
systems may be exacerbated by anthropogenic acidification through associated
processes that reduce the amount of dissolved organic carbon in lakes (Schindler
et aI., 1996; Yan et aI., 1996).
The effects of UV radiation (UVR) on zooplankton have, to date, focused on
acute exposures resulting in direct mortality or reductions in fecundity rather than
indirect influences such as food chain effects (Williamson et aI., 1994; Dey et aI.,
1988). Although such direct effects have been supported, studies that document
the indirect effects of UV-B radiation on lipid metabolism in zooplankton are just
M.T. Arts
optical-digital method to measure visible TAG and wax ester energy reserves in
calanoid copepods. They proposed that the distribution of storage lipids within the
body segments would be useful as a predictive and quantitative tool for monitoring and assessing the status of copepod populations with respect to their ability to
resist starvation or, alternatively, as an index of their recent feeding success.
Finally, in a study on the effects of acid stress on zooplankton communities,
Locke and Sprules (1993) stained zooplankton with a lipophilic dye (Sudan IV)
designed to accentuate the lipid stores in preserved samples (Bjorkman and
Shapiro, 1986). They demonstrated, using in situ enclosure experiments, that even
though some species of acid-tolerant species (e.g., Sida crystallina) persist in an
enclosure following acidification, their lipid energy reserves, as measured by their
lipid-ovary index scores, actually decreased. Interestingly, acid-tolerant species
that appeared to benefit from the reduced competition and increased food supplies
such as the cyclopoid copepods (e.g., Diacyclops thomasi) also contained increased levels of storage lipids (Locke and Sprules, 1993).
4.4.4. Fatty Acid Composition and Abundance
Examination of FA composition and abundance (FA profiles) in zooplankton in
relation to stress has not received the attention it deserves. Several examples in
algae (Mooney et aI., 1995; Sicko-Goad et al.. 1989) and periphyton (Napolitano
et aI., 1994) illustrate how FA profiles change as a function of stress. Because
zooplankton obtain their FAs from the diet, there is good reason to believe that
zooplankton FA profiles will also be affected by the presence of stressors. Because FAs are fundamental components of membranes, the effects of stressors on
FA composition and the subsequent health of zooplankton merit further attention.
4.5. Ultraviolet Radiation and Zooplankton Lipids
Significant reductions of stratospheric ozone have been observed over the past
decade, and there is concern that ultraviolet B (UV-B) radiation (300-320 nm)
reaching the earth's surface will also increase (Madronich, 1995). UV-B radiation
can penetrate to ecologically significant depths in natural waters, thus the observed increases in surface UV-B radiation have the potential to adversely affect
phytoplankton productivity, especially in shallow lakes, wetlands, and rivers.
There is new evidence to suggest that effects of UV-B radiation in freshwater
systems may be exacerbated by anthropogenic acidification through associated
processes that reduce the amount of dissolved organic carbon in lakes (Schindler
et aI., 1996; Yan et aI., 1996).
The effects of UV radiation (UVR) on zooplankton have, to date, focused on
acute exposures resulting in direct mortality or reductions in fecundity rather than
indirect influences such as food chain effects (Williamson et aI., 1994; Dey et aI.,
1988). Although such direct effects have been supported, studies that document
the indirect effects of UV-B radiation on lipid metabolism in zooplankton are just