22
G.E. Napolitano
occurrence and distribution of lipids in organisms and prompted similar studies in
fresh water. Some early analyses, however, are not very reliable due to loss of
polyunsaturated fatty acids (PUFA) and incomplete compound separations. This
chapter examines the use of fatty acids as biochemical markers of trophic relationships between species and as indicators of sources and sinks of organic matter in
freshwater ecosystems. I will only consider the occurrence of fatty acids in organisms and in the water column. For a discussion of fatty acids in sediments, readers
are referred to the reviews by Bourbonniere and Meyers (1996), Meyers and
Ishiwatari (1993), Parkes (1987), and Barnes and Barnes (1978).
2.2. Nomenclature
The shorthand nomenclature for fatty acids used here is of the form 18:20)6, in
which" 18" designates the total number of carbon atoms, "2" the number of cis
double bonds, and "0)6" the position of the first double bond (the "6" being
counted from the methyl end of the molecule). Thus, 18:20)6 is equivalent to
/l9, 12-18:2 and 18:30)3 is equivalent to /l9,12, 15-18:3. Double bonds in a PUFA
are separated by a -CH 2 group (methylene interrupted), unless otherwise stated.
The prefixes iso and anteiso refer to a fatty acid with a single methyl branch
located two or three carbons away from the terminal methyl group, respectively,
whereas br refers to a methyl branch in an unspecified location of the molecule.
2.3. Characteristics of Fatty Acid Markers for
Trophic Studies
The ideal fatty acid marker is uncommon in nature and yet can be quantitatively
extracted from biological and environmental samples and analyzed with appropriate sensitivity. Because lipid metabolism and storage in animals are organspecific, fatty acid markers should be extracted from individual tissues or body
parts. For example. the fatty acids in triacylglycerols of adipose tissue of animals
are particularly useful as trophic markers because they represent dietary fatty
acids (Henderson and Sargent, 1981; Leger et aI., 1981), whereas the liver accounts for most of the fatty acid synthesis by elongation and desaturation.
Another important aspect of fatty acid trophic markers is that the fatty acid
composition of an animal represents the time-integrated dietary intake. The
quantitative aspects of the integrative properties of dietary lipids are not well
studied and may be species-specific. Bourdier and Amblard (1989) addressed this
problem by performing feeding experiments with previously starved calanoid
copepods (Acanthodiaptomus denticomis). Their results indicated that the rate of
restoration of the lipid reserves depended on the algal species considered and that
no noticeable recovery was observed before the second day of feeding. They also
observed that the phospholipid fatty acid profile varied little between the starvation and feeding periods, but the fatty acids in storage lipids (e.g., 16: 10)7 and
G.E. Napolitano
occurrence and distribution of lipids in organisms and prompted similar studies in
fresh water. Some early analyses, however, are not very reliable due to loss of
polyunsaturated fatty acids (PUFA) and incomplete compound separations. This
chapter examines the use of fatty acids as biochemical markers of trophic relationships between species and as indicators of sources and sinks of organic matter in
freshwater ecosystems. I will only consider the occurrence of fatty acids in organisms and in the water column. For a discussion of fatty acids in sediments, readers
are referred to the reviews by Bourbonniere and Meyers (1996), Meyers and
Ishiwatari (1993), Parkes (1987), and Barnes and Barnes (1978).
2.2. Nomenclature
The shorthand nomenclature for fatty acids used here is of the form 18:20)6, in
which" 18" designates the total number of carbon atoms, "2" the number of cis
double bonds, and "0)6" the position of the first double bond (the "6" being
counted from the methyl end of the molecule). Thus, 18:20)6 is equivalent to
/l9, 12-18:2 and 18:30)3 is equivalent to /l9,12, 15-18:3. Double bonds in a PUFA
are separated by a -CH 2 group (methylene interrupted), unless otherwise stated.
The prefixes iso and anteiso refer to a fatty acid with a single methyl branch
located two or three carbons away from the terminal methyl group, respectively,
whereas br refers to a methyl branch in an unspecified location of the molecule.
2.3. Characteristics of Fatty Acid Markers for
Trophic Studies
The ideal fatty acid marker is uncommon in nature and yet can be quantitatively
extracted from biological and environmental samples and analyzed with appropriate sensitivity. Because lipid metabolism and storage in animals are organspecific, fatty acid markers should be extracted from individual tissues or body
parts. For example. the fatty acids in triacylglycerols of adipose tissue of animals
are particularly useful as trophic markers because they represent dietary fatty
acids (Henderson and Sargent, 1981; Leger et aI., 1981), whereas the liver accounts for most of the fatty acid synthesis by elongation and desaturation.
Another important aspect of fatty acid trophic markers is that the fatty acid
composition of an animal represents the time-integrated dietary intake. The
quantitative aspects of the integrative properties of dietary lipids are not well
studied and may be species-specific. Bourdier and Amblard (1989) addressed this
problem by performing feeding experiments with previously starved calanoid
copepods (Acanthodiaptomus denticomis). Their results indicated that the rate of
restoration of the lipid reserves depended on the algal species considered and that
no noticeable recovery was observed before the second day of feeding. They also
observed that the phospholipid fatty acid profile varied little between the starvation and feeding periods, but the fatty acids in storage lipids (e.g., 16: 10)7 and