8. Lipids and Essential Fatty Acids in Aquatic Food Webs
179
compiled from the literature (Table 8.1, references in legend) show that there are
pronounced differences in the fatty acid profiles of the various species but also
characteristic features for the taxonomic groups. All dinoflagellates contain high
levels of DHA, a moderate although variable content of EPA, and a high sum of
003 fatty acids. The heterotrophic dinoflagellate Cryptecodinium cohnii contains a
high level of DHA, whereas no other 003 fatty acid is present in significant
amounts «1 %). Among the C18 fatty acids, 18:4003 appears to be most common.
The diatoms are, by contrast, characterized by a high level of EPA and a low
content of other 003 fatty acids. Some diatom species contain minor quantities of
18:4003 and DHA, but EPA is generally prominent. Some chrysophytes exhibit a
moderate or high DHA and EPA content, whereas others contain relatively high
amounts of short-chain 003 fatty acids (18:3003, 18:4003). The variability in 003
fatty acid content is also pronounced in the green algae. Only small amounts of
DHA are found, but some species contain relatively high contents of EPA while
having little of shorter 003 fatty acids. Some green algae exhibit relatively low
levels of 003 fatty acids.
The fatty acid profiles of marine algae are somewhat dependent on the culture
conditions. In both marine and freshwater algae, the percentage 003 fatty acids of
total fatty acids tends to be slightly higher in nutrient-sufficient than in nutrientdeficient cells, whereas deficient cells contain a higher fraction of saturated and
monounsaturated fatty acids (e.g., 16:0 and 18:1) (Reitan et al., 1994b; Siron et
al., 1989). The effect of culture conditions on the fatty acid composition of algae is
usually less pronounced than the broad range of fatty acid compositions found
among species.
A high percentage 003 fatty acids in nutrient-sufficient algae is not necessarily
equivalent to a higher quantitative content of these fatty acids, at least not in lipidstoring species. This is because of the antagonistic effect of enhanced quantitative
003 content under nutrient limitation, which tends to counteract the effect of
reduced percentage content.
8.2.6.1.3. Conclusion
A general conclusion regarding fatty acid profiles of algae is that dinoflagellates
are rich in DHA; diatoms are rich in EPA; chrysophytes show variable 003 profiles
with either 18:3,18:4, EPA, or DHA as the dominant 003 fatty acid; and the diverse
group of green algae shows even more variable profiles, with 18:3, 18:4, or EPA
as the dominant 003 fatty acids. Some species exhibit a high content of a single 003
fatty acid in combination with relatively low levels of the others. The high content
and purity of DHA in many dinoflagellates and in some chrysophytes are noteworthy. Oils derived from marine animals are generally more complex and
balanced.
Changes in the growth conditions (e.g., light intensity, nutrient availability)
will most likely affect the level of total lipids more strongly than the fatty acid
distribution in lipid-storing algae, whereas the same manipulations will affect the
lipid content of carbohydrate-storing species only moderately. Generally, it may
179
compiled from the literature (Table 8.1, references in legend) show that there are
pronounced differences in the fatty acid profiles of the various species but also
characteristic features for the taxonomic groups. All dinoflagellates contain high
levels of DHA, a moderate although variable content of EPA, and a high sum of
003 fatty acids. The heterotrophic dinoflagellate Cryptecodinium cohnii contains a
high level of DHA, whereas no other 003 fatty acid is present in significant
amounts «1 %). Among the C18 fatty acids, 18:4003 appears to be most common.
The diatoms are, by contrast, characterized by a high level of EPA and a low
content of other 003 fatty acids. Some diatom species contain minor quantities of
18:4003 and DHA, but EPA is generally prominent. Some chrysophytes exhibit a
moderate or high DHA and EPA content, whereas others contain relatively high
amounts of short-chain 003 fatty acids (18:3003, 18:4003). The variability in 003
fatty acid content is also pronounced in the green algae. Only small amounts of
DHA are found, but some species contain relatively high contents of EPA while
having little of shorter 003 fatty acids. Some green algae exhibit relatively low
levels of 003 fatty acids.
The fatty acid profiles of marine algae are somewhat dependent on the culture
conditions. In both marine and freshwater algae, the percentage 003 fatty acids of
total fatty acids tends to be slightly higher in nutrient-sufficient than in nutrientdeficient cells, whereas deficient cells contain a higher fraction of saturated and
monounsaturated fatty acids (e.g., 16:0 and 18:1) (Reitan et al., 1994b; Siron et
al., 1989). The effect of culture conditions on the fatty acid composition of algae is
usually less pronounced than the broad range of fatty acid compositions found
among species.
A high percentage 003 fatty acids in nutrient-sufficient algae is not necessarily
equivalent to a higher quantitative content of these fatty acids, at least not in lipidstoring species. This is because of the antagonistic effect of enhanced quantitative
003 content under nutrient limitation, which tends to counteract the effect of
reduced percentage content.
8.2.6.1.3. Conclusion
A general conclusion regarding fatty acid profiles of algae is that dinoflagellates
are rich in DHA; diatoms are rich in EPA; chrysophytes show variable 003 profiles
with either 18:3,18:4, EPA, or DHA as the dominant 003 fatty acid; and the diverse
group of green algae shows even more variable profiles, with 18:3, 18:4, or EPA
as the dominant 003 fatty acids. Some species exhibit a high content of a single 003
fatty acid in combination with relatively low levels of the others. The high content
and purity of DHA in many dinoflagellates and in some chrysophytes are noteworthy. Oils derived from marine animals are generally more complex and
balanced.
Changes in the growth conditions (e.g., light intensity, nutrient availability)
will most likely affect the level of total lipids more strongly than the fatty acid
distribution in lipid-storing algae, whereas the same manipulations will affect the
lipid content of carbohydrate-storing species only moderately. Generally, it may