82
M.T. Arts
affecting zooplankton nutntlOn, survival, and reproduction. Still, many unanswered questions remain.
4.6.1. Geographical Disparities
Most of the work that has been done on lipid dynamics of freshwater zooplankton
comes from the midlatitudes and, most commonly, from the Northern Hemisphere. Studies on high-altitude or tropical zooplankton populations (Wyngaard et
aI., 1994) are comparatively rare. Also notably absent are studies on lipid energetics, FA composition from some of the world's ancient lakes such as the African
rift lakes and Lake Baikal (however, see Morris, 1983). These lakes with their
endemic zooplankton species (e.g., the calanoid copepod Epischura baikalensis)
and lipid-rich phytoplankton species (e.g., Botryococcus braunii) may well provide unique insights into novel manifestations of lipid dynamics and strategies in
situations in which the evolutionary relationships among organisms have been
maintained in relative isolation for millennia. Equally important is the opportunity
to document present "baseline" lipid contents for a variety of species now subject
to increasing anthropogenic stress in these systems.
4.6.2. Physicochemical Disparities
The total volume of the world's inland saline lakes is only slightly less (~83%)
than that of freshwater lakes (Hammer, 1986). The definition of saline is still
debated, but the one that curries the most favor is that saline lakes are lakes where
the salt concentration exceeds 3.0 mg . L - 1 (Hammer, 1986). Applying this
definition to all inland lakes means that there are a substantial number of "saline"
waters that presently support "freshwater" zooplankton such as Daphnia. One
such lake is saline (total dissolved solids = 21 mg . L -1) Redberry Lake in central
Saskatchewan, which has viable populations of D. pulex and Diaptomus sicilis
(Arts et aI., 1993). Thus, many saline lakes (some of them quite large) support
viable daphnid and copepod populations. The lipid chemistry and ecology of
zooplankton inhabiting these inland saline lakes are poorly understood. For example, it is unknown whether nutrient limitation or EFA limitation (or food quality in
the broadest sense) or predation is the dominant mechanism limiting Daphnia,
copepods, or rotiters. The food webs and nutrient regimes in these systems often
deviate substantially from the more familiar points of reference (i.e., the freshwater lakes). Food chain length and complexity become increasingly truncated along
salinity gradients producing more "simplified" communities (i.e .. shorter and few
links). Because of this inherent simplicity. these communities provide useful
natural laboratories for the examination of the effects of perturbation, food quality, temperature, and so on on lipid energy transfers and fatty acid composition
and abundance. In more simplified communities, it is potentially easier to ascribe
"cause and etlecf' to observations made following natural or artificial perturbations because the links are fewer. and therefore transfers of biomolecules from one
trophic level to the next are likely to be more direct.
M.T. Arts
affecting zooplankton nutntlOn, survival, and reproduction. Still, many unanswered questions remain.
4.6.1. Geographical Disparities
Most of the work that has been done on lipid dynamics of freshwater zooplankton
comes from the midlatitudes and, most commonly, from the Northern Hemisphere. Studies on high-altitude or tropical zooplankton populations (Wyngaard et
aI., 1994) are comparatively rare. Also notably absent are studies on lipid energetics, FA composition from some of the world's ancient lakes such as the African
rift lakes and Lake Baikal (however, see Morris, 1983). These lakes with their
endemic zooplankton species (e.g., the calanoid copepod Epischura baikalensis)
and lipid-rich phytoplankton species (e.g., Botryococcus braunii) may well provide unique insights into novel manifestations of lipid dynamics and strategies in
situations in which the evolutionary relationships among organisms have been
maintained in relative isolation for millennia. Equally important is the opportunity
to document present "baseline" lipid contents for a variety of species now subject
to increasing anthropogenic stress in these systems.
4.6.2. Physicochemical Disparities
The total volume of the world's inland saline lakes is only slightly less (~83%)
than that of freshwater lakes (Hammer, 1986). The definition of saline is still
debated, but the one that curries the most favor is that saline lakes are lakes where
the salt concentration exceeds 3.0 mg . L - 1 (Hammer, 1986). Applying this
definition to all inland lakes means that there are a substantial number of "saline"
waters that presently support "freshwater" zooplankton such as Daphnia. One
such lake is saline (total dissolved solids = 21 mg . L -1) Redberry Lake in central
Saskatchewan, which has viable populations of D. pulex and Diaptomus sicilis
(Arts et aI., 1993). Thus, many saline lakes (some of them quite large) support
viable daphnid and copepod populations. The lipid chemistry and ecology of
zooplankton inhabiting these inland saline lakes are poorly understood. For example, it is unknown whether nutrient limitation or EFA limitation (or food quality in
the broadest sense) or predation is the dominant mechanism limiting Daphnia,
copepods, or rotiters. The food webs and nutrient regimes in these systems often
deviate substantially from the more familiar points of reference (i.e., the freshwater lakes). Food chain length and complexity become increasingly truncated along
salinity gradients producing more "simplified" communities (i.e .. shorter and few
links). Because of this inherent simplicity. these communities provide useful
natural laboratories for the examination of the effects of perturbation, food quality, temperature, and so on on lipid energy transfers and fatty acid composition
and abundance. In more simplified communities, it is potentially easier to ascribe
"cause and etlecf' to observations made following natural or artificial perturbations because the links are fewer. and therefore transfers of biomolecules from one
trophic level to the next are likely to be more direct.