6. Seasonal Dynamics of Lipids
123
lipids and protein. An OIN ratio of 50 is considered the lower limit for physiological health in the blue mussel, Mytilus edulis (Bayne et aI., 1985). In August,
Dreissena had an OIN ratio of 16 that signified high use of protein, probably from
the catabolism of soft body tissues because Dreissena mass and lipid declined
from April to August (Nalepa et al., 1993). However, a low ratio could also signify
the use of a high-protein food source. During the fall months, the zebra mussel's
OIN ratio increased to 30, but this number is still below the physiologically
healthy ratio (Quigley et al., 1993). Thus, despite Dreissena's rapid increase in
densities since their successful invasion of North America, they may not be in a
healthy state in all locales, likely due to food limitation during certain times of the
year.
6.3. Research Needs
FA characterization in marine organisms has enhanced our understanding of food
web dynamics in many marine ecosystems, but this approach has not been used as
extensively in freshwater environments. FA biomarkers could likely, in freshwater ecosystems, trace food web dynamics as has been done for marine ecosystems
(Kattner et aI., 1996; St. John and Lund, 1996; Kattner and Hagen, 1995; Parrish
et aI., 1995; Kattner, 1989; Napolitano and Ackman, 1989). For example, in
Jeddore Harbour, Nova Scotia, the appearance of odd-chain FAs in smelt were
eventually traced to PontoporeiaJemorata (a marine relative of Diporeia spp.).
Pontoporeia Jemorata was a significant part of the smelt diet in the spring when
actively reproductive males swam in the water column (Paradis and Ackman,
1976). The odd-chain FAs may have originated from microbes or allochthonous
sources in the harbor (Paradis and Ackman, 1977).
FA characterization of freshwater organisms is very limited, especially for
benthic invertebrates. However, some FA analysis has been done for Diplodon
spp. (Pollero et aI., 1983, 1981; Pollero and Brenner, 1981), aquatic insects (Bell
et aI., 1994; Hanson et aI., 1985, 1983; Lee et aI., 1975), and nectobenthic
amphipods from Lake Baikal (Dembitsky et al., 1994; Morris, 1984). In the Great
Lakes, identification of FA biomarkers in Diporeia or oligochaetes could possibly
be used to trace seasonal changes in their diet, and these biomarkers might
eventually be traced to their consumers such as mysids and fish.
Several FAs are essential to organisms at various trophic levels. Invertebrates
and fish must obtain essential FAs from their diet for proper development and
reproduction. Some FAs are important precursors to hormones. For example, the
FA compositions of river invertebrates that are the natural food to salmon were
examined and compared with the FA composition of commercial diets fed to
farmed salmon (Bell et aI., 1994). Although essential FAs were present in the
commercial diet, important FA ratios were not optimal for salmon undergoing
smoltification. A diet with FA ratios closer to that found in the salmon's natural
diet of freshwater invertebrates prevented certain pathologies from developing in
the fish.
123
lipids and protein. An OIN ratio of 50 is considered the lower limit for physiological health in the blue mussel, Mytilus edulis (Bayne et aI., 1985). In August,
Dreissena had an OIN ratio of 16 that signified high use of protein, probably from
the catabolism of soft body tissues because Dreissena mass and lipid declined
from April to August (Nalepa et al., 1993). However, a low ratio could also signify
the use of a high-protein food source. During the fall months, the zebra mussel's
OIN ratio increased to 30, but this number is still below the physiologically
healthy ratio (Quigley et al., 1993). Thus, despite Dreissena's rapid increase in
densities since their successful invasion of North America, they may not be in a
healthy state in all locales, likely due to food limitation during certain times of the
year.
6.3. Research Needs
FA characterization in marine organisms has enhanced our understanding of food
web dynamics in many marine ecosystems, but this approach has not been used as
extensively in freshwater environments. FA biomarkers could likely, in freshwater ecosystems, trace food web dynamics as has been done for marine ecosystems
(Kattner et aI., 1996; St. John and Lund, 1996; Kattner and Hagen, 1995; Parrish
et aI., 1995; Kattner, 1989; Napolitano and Ackman, 1989). For example, in
Jeddore Harbour, Nova Scotia, the appearance of odd-chain FAs in smelt were
eventually traced to PontoporeiaJemorata (a marine relative of Diporeia spp.).
Pontoporeia Jemorata was a significant part of the smelt diet in the spring when
actively reproductive males swam in the water column (Paradis and Ackman,
1976). The odd-chain FAs may have originated from microbes or allochthonous
sources in the harbor (Paradis and Ackman, 1977).
FA characterization of freshwater organisms is very limited, especially for
benthic invertebrates. However, some FA analysis has been done for Diplodon
spp. (Pollero et aI., 1983, 1981; Pollero and Brenner, 1981), aquatic insects (Bell
et aI., 1994; Hanson et aI., 1985, 1983; Lee et aI., 1975), and nectobenthic
amphipods from Lake Baikal (Dembitsky et al., 1994; Morris, 1984). In the Great
Lakes, identification of FA biomarkers in Diporeia or oligochaetes could possibly
be used to trace seasonal changes in their diet, and these biomarkers might
eventually be traced to their consumers such as mysids and fish.
Several FAs are essential to organisms at various trophic levels. Invertebrates
and fish must obtain essential FAs from their diet for proper development and
reproduction. Some FAs are important precursors to hormones. For example, the
FA compositions of river invertebrates that are the natural food to salmon were
examined and compared with the FA composition of commercial diets fed to
farmed salmon (Bell et aI., 1994). Although essential FAs were present in the
commercial diet, important FA ratios were not optimal for salmon undergoing
smoltification. A diet with FA ratios closer to that found in the salmon's natural
diet of freshwater invertebrates prevented certain pathologies from developing in
the fish.