2. Fatty Acids as Trophic and Chemical Markers
25
ence of detritus, animal remains, and a variable number of unidentified algae in
the sample (including epiphytic species).
Saturated fatty acids (SAFA) 14:0, 16:0, and 18:0 are of little taxonomic value
as biochemical markers because they are readily synthesized by most organisms
and occur at various levels of concentrations in all algal groups (Table 2.1).
Among the monounsaturated fatty acids (MUFA), 16:10)7, 18:10)7, and 18:10)9
are potentially useful markers. Palmitoleic acid (16: 10)7) is the primary product of
the ~9 desaturase during the synthesis of unsaturated fatty acids in both plants and
animals, explaining the wide distribution of this fatty acid in nature. Nevertheless,
the distribution of 16: 1 0)7 among algae is far from homogeneous. Palmitoleic acid
is a major, often prominent, constituent of the lipids of diatoms (Sicko-Goad,
1988; Wood, 1988, 1974) and some cyanobacteria (Ahlgren et aI., 1992; Murata et
aI., 1992), sometimes exceeding concentrations of 30% of the total fatty acids.
16:10)7 is much less abundant (>5% of the total fatty acids) in cultures and
natural populations of green algae (Napolitano et aI., 1994) and dinoflagellates
(Ahlgren et aI., 1992) (Table 2.1). Palmitoleic acid is a major fatty acid (15%) in
the lipids of Vaucheria sp. (Xanthophyceae), an inhabitant of damp soils and
stream banks (Nichols and Appleby, 1969).
The two major C18 MUFAs, 18: 10)7 (cis-vaccenic) and 18: 10)9 (oleic) acids,
are potentially important biochemical markers. However, the lack of separation
between these two fatty acids during earlier analyses performed on packed GC
columns limits the use of the available information. Even today, when capillary
columns provide complete separation of C 18 MUFA, it is common to find reports
with tables of fatty acid compositions with a single entry for" 18: I."
Cis-vaccenic acid (18: 10)7) is a rather minor fatty acid in eucaryotic algae,
normally accounting for 1-2% of the total fatty acids. Although lipids of marine
cyanobacteria (e.g., Synechococcus sp.) may contain high proportions of 18:10)7
(i.e., 21.l %) (Goodloe and Light, 1982), most recent analyses of freshwater
cyanobacteria revealed a concentration of between 0.5-3.1 % (Ahlgren et aI.,
1992, 1990). Murata et al. (1992) reported that 18: 10)7 plus 18: I 0)9 made up 24 %
of the total fatty acids in the lipids of a filamentous strain of Anabaena variabilis;
the authors, however, did not refer to the relative contribution of each isomer.
Oleic acid (18: 10)9) is typically a major fatty acid in dinoflagellates and in some
green algae (Ahlgren et aI., 1992). Many analyses of natural algal populations
frequently show high concentrations of 18:10)9 in their lipids (Table 2.1). However, considering that 18:10)9 may also be an important constituent of animal
lipids and is relatively resistant to photodegradation (Armstrong et aI., 1966), its
presence in the particulate organic matter (POM) may also reflect the contribution
of animal detritus.
Algae's PUFAs are important biochemical markers because they include some
essential fatty acids that animals must assimilate from their diet. The interpretation of PUFA data reported in the literature must be exercised with caution,
however, because identification is often based on GC retention data, without
further derivatization or GC/mass spectrometry structural confirmation. C 16
25
ence of detritus, animal remains, and a variable number of unidentified algae in
the sample (including epiphytic species).
Saturated fatty acids (SAFA) 14:0, 16:0, and 18:0 are of little taxonomic value
as biochemical markers because they are readily synthesized by most organisms
and occur at various levels of concentrations in all algal groups (Table 2.1).
Among the monounsaturated fatty acids (MUFA), 16:10)7, 18:10)7, and 18:10)9
are potentially useful markers. Palmitoleic acid (16: 10)7) is the primary product of
the ~9 desaturase during the synthesis of unsaturated fatty acids in both plants and
animals, explaining the wide distribution of this fatty acid in nature. Nevertheless,
the distribution of 16: 1 0)7 among algae is far from homogeneous. Palmitoleic acid
is a major, often prominent, constituent of the lipids of diatoms (Sicko-Goad,
1988; Wood, 1988, 1974) and some cyanobacteria (Ahlgren et aI., 1992; Murata et
aI., 1992), sometimes exceeding concentrations of 30% of the total fatty acids.
16:10)7 is much less abundant (>5% of the total fatty acids) in cultures and
natural populations of green algae (Napolitano et aI., 1994) and dinoflagellates
(Ahlgren et aI., 1992) (Table 2.1). Palmitoleic acid is a major fatty acid (15%) in
the lipids of Vaucheria sp. (Xanthophyceae), an inhabitant of damp soils and
stream banks (Nichols and Appleby, 1969).
The two major C18 MUFAs, 18: 10)7 (cis-vaccenic) and 18: 10)9 (oleic) acids,
are potentially important biochemical markers. However, the lack of separation
between these two fatty acids during earlier analyses performed on packed GC
columns limits the use of the available information. Even today, when capillary
columns provide complete separation of C 18 MUFA, it is common to find reports
with tables of fatty acid compositions with a single entry for" 18: I."
Cis-vaccenic acid (18: 10)7) is a rather minor fatty acid in eucaryotic algae,
normally accounting for 1-2% of the total fatty acids. Although lipids of marine
cyanobacteria (e.g., Synechococcus sp.) may contain high proportions of 18:10)7
(i.e., 21.l %) (Goodloe and Light, 1982), most recent analyses of freshwater
cyanobacteria revealed a concentration of between 0.5-3.1 % (Ahlgren et aI.,
1992, 1990). Murata et al. (1992) reported that 18: 10)7 plus 18: I 0)9 made up 24 %
of the total fatty acids in the lipids of a filamentous strain of Anabaena variabilis;
the authors, however, did not refer to the relative contribution of each isomer.
Oleic acid (18: 10)9) is typically a major fatty acid in dinoflagellates and in some
green algae (Ahlgren et aI., 1992). Many analyses of natural algal populations
frequently show high concentrations of 18:10)9 in their lipids (Table 2.1). However, considering that 18:10)9 may also be an important constituent of animal
lipids and is relatively resistant to photodegradation (Armstrong et aI., 1966), its
presence in the particulate organic matter (POM) may also reflect the contribution
of animal detritus.
Algae's PUFAs are important biochemical markers because they include some
essential fatty acids that animals must assimilate from their diet. The interpretation of PUFA data reported in the literature must be exercised with caution,
however, because identification is often based on GC retention data, without
further derivatization or GC/mass spectrometry structural confirmation. C 16