4. Lipids in Freshwater Zooplankton
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trolling the length of time a bloom remains dominant (through direct suppression of zooplankton feeding), chemical deterrents may be able to affect phytoplankton community structure while simultaneously exerting direct control on
zooplankton production rates. Because of these direct and indirect effects on
zooplankton community structure and production, allelopathic and chemical
deterrent compounds have the potential to affect the rate of energy transfers in
pelagic ecosystems. Research into the identification and characterization of these
compounds has progressed faster for marine than for freshwater systems because
of the discernable threat to and possible usefulness of these compounds to the
mariculture industry. For example, allelopathic compounds show great promise in
terms of reducing the abundance of "undesirable" or "nuisance" species in pondor tank-rearing systems designed to grow algal species for the production of
economically important compounds. Also, in terms of harvesting wild-species
with desirable chemical constituents (i.e., "biomolecular farming"), application of
allelopathic compounds at key periods may be a useful way of maximizing yields
from natural systems. Finally, allelopathic chemicals may, in the future, serve an
important role as antifouling compounds. More research into the chemical structure and role of these allelopathic compounds in freshwater ecosystems is clearly
required before the detailed mechanisms and generality of their use in controlling
algal and zooplankton production and community composition can be assessed.
4.7. Conclusions
Lipids, particularly energy reserve lipids, are sensitive to environmental perturbation, both natural and anthropogenic. This feature makes lipids a useful marker of
stress. The ratio of storage to membrane lipids, maternal lipid investment, and the
tracking of visible lipid energy stores are potentially useful indices of stress in
zooplankton. Changes in FA profiles as an index of stress in zooplankton is an
area that holds great promise but it is also one in which more research and
validation are urgently required.
The various expressions of energy reserve lipids (lipid content and concentration, areal energy reserves, and the visible lipid indices) provide unique perspectives on the physiological status of zooplankton and the relative contribution each
species makes to the standing pools of storage lipid energy in freshwater ecosystems. By monitoring changes in these standing stocks of storage lipids, one can
gain insights into the time course of lipid deposition and loss rates in organisms
both within and between trophic levels.
The presence of UVR is a fact of existence for pelagic organisms; however,
recent evidence suggesting that UV-B radiation is increasing has raised concerns.
Rates of photosynthesis are clearly depressed in many algae and some marine
algae have demonstrated altered FA profiles following exposure to realistic fluxes
of UV-B. Perhaps more significantly, these changes in FAs include reductions in
some of the EFAs. The implications of these reductions in EFAs following exposure to UV-B radiation in terms of survival and production rates of freshwater
zooplankton should prove an interesting challenge.
85
trolling the length of time a bloom remains dominant (through direct suppression of zooplankton feeding), chemical deterrents may be able to affect phytoplankton community structure while simultaneously exerting direct control on
zooplankton production rates. Because of these direct and indirect effects on
zooplankton community structure and production, allelopathic and chemical
deterrent compounds have the potential to affect the rate of energy transfers in
pelagic ecosystems. Research into the identification and characterization of these
compounds has progressed faster for marine than for freshwater systems because
of the discernable threat to and possible usefulness of these compounds to the
mariculture industry. For example, allelopathic compounds show great promise in
terms of reducing the abundance of "undesirable" or "nuisance" species in pondor tank-rearing systems designed to grow algal species for the production of
economically important compounds. Also, in terms of harvesting wild-species
with desirable chemical constituents (i.e., "biomolecular farming"), application of
allelopathic compounds at key periods may be a useful way of maximizing yields
from natural systems. Finally, allelopathic chemicals may, in the future, serve an
important role as antifouling compounds. More research into the chemical structure and role of these allelopathic compounds in freshwater ecosystems is clearly
required before the detailed mechanisms and generality of their use in controlling
algal and zooplankton production and community composition can be assessed.
4.7. Conclusions
Lipids, particularly energy reserve lipids, are sensitive to environmental perturbation, both natural and anthropogenic. This feature makes lipids a useful marker of
stress. The ratio of storage to membrane lipids, maternal lipid investment, and the
tracking of visible lipid energy stores are potentially useful indices of stress in
zooplankton. Changes in FA profiles as an index of stress in zooplankton is an
area that holds great promise but it is also one in which more research and
validation are urgently required.
The various expressions of energy reserve lipids (lipid content and concentration, areal energy reserves, and the visible lipid indices) provide unique perspectives on the physiological status of zooplankton and the relative contribution each
species makes to the standing pools of storage lipid energy in freshwater ecosystems. By monitoring changes in these standing stocks of storage lipids, one can
gain insights into the time course of lipid deposition and loss rates in organisms
both within and between trophic levels.
The presence of UVR is a fact of existence for pelagic organisms; however,
recent evidence suggesting that UV-B radiation is increasing has raised concerns.
Rates of photosynthesis are clearly depressed in many algae and some marine
algae have demonstrated altered FA profiles following exposure to realistic fluxes
of UV-B. Perhaps more significantly, these changes in FAs include reductions in
some of the EFAs. The implications of these reductions in EFAs following exposure to UV-B radiation in terms of survival and production rates of freshwater
zooplankton should prove an interesting challenge.