84
M.T. Arts
significant role in overwintering survivorship and/or in the ability of organisms to
colonize particular environments. A large body of literature, particularly in fish
and mammals, relates to the effects of changes in membrane FAs on membrane
fluidity (Gurr and Harwood, 1991). Information on algae (Nishida and Murata,
1996; Tatsuzawa et aI., 1996) and zooplankton (Farkas et aI., 1984, 1981; Farkas,
1979), particularly from freshwater species, is comparatively rare. Recent predictions concerning the effects of climate change suggest that increases in air temperature over a 20-year period (1970-1990) have resulted in increases in the
length of the ice-free season, mean and maximum water temperature, and the heat
contents of boreal forest lakes (Schindler et aI., 1990). Given these trends in
temperature, there is a need to better quantify the relationships among membrane
FA composition, membrane fluidity, overwintering success, and colonization
ability of organisms.
4.6.5. Diapause
Diapause is a potent phenomenon structuring pelagic zooplankton communities
(Dahms, 1995; Hairston et aI., 1995; Santer and Lampert, 1995). Resting stages
function to replenish populations following periods when conditions for the active
stages become uninhabitable. Diapausing eggs can be centuries old and still be
viable (Hairston et aI., 1995). Given that EFAs are so vital to the health of mature
animals, the FA composition and in particular EFA concentration in the diet may
have a significant effect on the viability of resting eggs (see 16nasd6ttir and
Kiorboe, 1996). In a similar manner, the survivorship and growth of newly
hatched Daphnia from ephippia may well be influenced by the concentrations and
composition of FAs in the resting stages. Because lipids play such a crucial role
both in the maintenance of cell membrane functionality and as metabolic fuel for
newly hatched animals, FA composition likely has an important role to play in the
viability of resting stages.
4.6.6. Lipids as Allelopathic Compounds and Chemical
Feeding Deterrents
It is now known that algae produce compounds that inhibit the growth of other
algae or sometimes themselves (auto-growth inhibition). This phenomenon is
called allelopathy, and there are examples from both the marine (Kakisawa et aI.,
1988) and freshwater (Yamada et aI., 1993) literature. Allelopathic compounds
are typically unsaturated FAs (Suzuki et aI., 1996; Yamada et aI., 1993; Kakisawa
et aI., 1988) or other compounds that fit the broad definition of lipid. Some of the
compounds produced by algae also deter the feeding of zooplankton (Shaw et aI.,
1995a,b) or other invertebrates such as gastropods (Sawai et aI., 1994). As with
the allelopathic compounds, chemical deterrents are often lipidic in nature (Shaw
et aI., 1995a,b; Sawai et a!., 1994).
By suppressing the growth of other algal species, allelopathic compounds can
indirectly affect zooplankton community structure and production rates. By con-
M.T. Arts
significant role in overwintering survivorship and/or in the ability of organisms to
colonize particular environments. A large body of literature, particularly in fish
and mammals, relates to the effects of changes in membrane FAs on membrane
fluidity (Gurr and Harwood, 1991). Information on algae (Nishida and Murata,
1996; Tatsuzawa et aI., 1996) and zooplankton (Farkas et aI., 1984, 1981; Farkas,
1979), particularly from freshwater species, is comparatively rare. Recent predictions concerning the effects of climate change suggest that increases in air temperature over a 20-year period (1970-1990) have resulted in increases in the
length of the ice-free season, mean and maximum water temperature, and the heat
contents of boreal forest lakes (Schindler et aI., 1990). Given these trends in
temperature, there is a need to better quantify the relationships among membrane
FA composition, membrane fluidity, overwintering success, and colonization
ability of organisms.
4.6.5. Diapause
Diapause is a potent phenomenon structuring pelagic zooplankton communities
(Dahms, 1995; Hairston et aI., 1995; Santer and Lampert, 1995). Resting stages
function to replenish populations following periods when conditions for the active
stages become uninhabitable. Diapausing eggs can be centuries old and still be
viable (Hairston et aI., 1995). Given that EFAs are so vital to the health of mature
animals, the FA composition and in particular EFA concentration in the diet may
have a significant effect on the viability of resting eggs (see 16nasd6ttir and
Kiorboe, 1996). In a similar manner, the survivorship and growth of newly
hatched Daphnia from ephippia may well be influenced by the concentrations and
composition of FAs in the resting stages. Because lipids play such a crucial role
both in the maintenance of cell membrane functionality and as metabolic fuel for
newly hatched animals, FA composition likely has an important role to play in the
viability of resting stages.
4.6.6. Lipids as Allelopathic Compounds and Chemical
Feeding Deterrents
It is now known that algae produce compounds that inhibit the growth of other
algae or sometimes themselves (auto-growth inhibition). This phenomenon is
called allelopathy, and there are examples from both the marine (Kakisawa et aI.,
1988) and freshwater (Yamada et aI., 1993) literature. Allelopathic compounds
are typically unsaturated FAs (Suzuki et aI., 1996; Yamada et aI., 1993; Kakisawa
et aI., 1988) or other compounds that fit the broad definition of lipid. Some of the
compounds produced by algae also deter the feeding of zooplankton (Shaw et aI.,
1995a,b) or other invertebrates such as gastropods (Sawai et aI., 1994). As with
the allelopathic compounds, chemical deterrents are often lipidic in nature (Shaw
et aI., 1995a,b; Sawai et a!., 1994).
By suppressing the growth of other algal species, allelopathic compounds can
indirectly affect zooplankton community structure and production rates. By con-