2. Fatty Acids as Trophic and Chemical Markers
23
18: 1 co7) reflected those of the algal food after 20 days offeeding. Examinations of
the gut content of an animal provide information of the last ingesta; lipid analyses
integrate the processes of feeding, absorption, and deposition of energy reserves
over a much longer period of time (see Arts, this volume).
2.4. Primary Sources and Trophic Transfer of Fatty Acids
2.4.1. Fatty Acid Composition of Algae and Cyanobacteria
Algae are at the base of the trophic ladder of aquatic ecosystems, providing energy
and essential nutrients for primary consumers. The major acyl lipid classes in
algae are phospholipids (e.g., phosphatidylcholine, phosphatidylethanolamine,
phosphatidylserine, phosphatidylglycerol, phoasphatidylinositol), glycolipids
(monogalactosyldiglycerol, digalactosyl glycerol, sulfolipids), triacylglycerols,
sterol esters, and free fatty acids (Dembitsky and Rozentsvet, 1996; Douce et aI.,
1990; Pohl and Zurheide, 1982; Wood, 1974). Phospholipids are structural constituents of cellular membranes, whereas glycolipids are major components of the
thylakoid membrane in chloroplasts (Douce et aI., 1990). The triacylglycerols of
algae are intracellular storage materials and can occur as clearly visible oil droplets (Vechtel et aI., 1992; Wood, 1988). Sterol esters are normally minor lipid
constituents in plants, and their cellular function is not clear (Petko v and Furnadzieva, 1993).
Fatty acids rarely occur in the nonesterified form (free fatty acids) at concentrations of more than a few percentages of the total lipids of intact or well-preserved
plant cells (Parrish et aI., 1991); large concentrations of free fatty acids are almost
certainly related to enzymatic autolysis of lipids, primarily of phospholipids (Galliard, 1980). The recurrent reports on relatively high levels of free fatty acids in
plant samples are likely to be the result of the activity of powerful lipases.
Moreover, certain plant lipases can maintain their activity at very low temperatures and even in the presence of some of the organic solvents used in lipid
extraction procedures (Parrish et aI., 1991; Christie, 1982).
Analysis of fatty acids in natural populations of freshwater algae are not common and are limited to cyanobacteria (Kenyon, 1972; Kenyon et a\., 1972) and
several species of green algae and flagellates (including dinoflagellates and
chrysophytes) (Cranwell et aI., 1990, 1988). Although diatoms are among the
major primary producers in freshwater ecosystems, their fatty acid compositions
have not been adequately studied. The fatty acid composition of natural and
laboratory algal populations can change dramatically as a function of environmental factors such as temperature, nutrient concentrations, and light (see Wainman et aI., this volume), and these variations are the consequence of a number of
interdependent factors affecting the cell cycle, lipid class composition, or membrane fluidity. Despite these adaptations to changing physiological and environmental conditions, there is a clear relationship between algal fatty acid
composition and taxa status. Table 2.1 presents examples of the fatty acid com-
23
18: 1 co7) reflected those of the algal food after 20 days offeeding. Examinations of
the gut content of an animal provide information of the last ingesta; lipid analyses
integrate the processes of feeding, absorption, and deposition of energy reserves
over a much longer period of time (see Arts, this volume).
2.4. Primary Sources and Trophic Transfer of Fatty Acids
2.4.1. Fatty Acid Composition of Algae and Cyanobacteria
Algae are at the base of the trophic ladder of aquatic ecosystems, providing energy
and essential nutrients for primary consumers. The major acyl lipid classes in
algae are phospholipids (e.g., phosphatidylcholine, phosphatidylethanolamine,
phosphatidylserine, phosphatidylglycerol, phoasphatidylinositol), glycolipids
(monogalactosyldiglycerol, digalactosyl glycerol, sulfolipids), triacylglycerols,
sterol esters, and free fatty acids (Dembitsky and Rozentsvet, 1996; Douce et aI.,
1990; Pohl and Zurheide, 1982; Wood, 1974). Phospholipids are structural constituents of cellular membranes, whereas glycolipids are major components of the
thylakoid membrane in chloroplasts (Douce et aI., 1990). The triacylglycerols of
algae are intracellular storage materials and can occur as clearly visible oil droplets (Vechtel et aI., 1992; Wood, 1988). Sterol esters are normally minor lipid
constituents in plants, and their cellular function is not clear (Petko v and Furnadzieva, 1993).
Fatty acids rarely occur in the nonesterified form (free fatty acids) at concentrations of more than a few percentages of the total lipids of intact or well-preserved
plant cells (Parrish et aI., 1991); large concentrations of free fatty acids are almost
certainly related to enzymatic autolysis of lipids, primarily of phospholipids (Galliard, 1980). The recurrent reports on relatively high levels of free fatty acids in
plant samples are likely to be the result of the activity of powerful lipases.
Moreover, certain plant lipases can maintain their activity at very low temperatures and even in the presence of some of the organic solvents used in lipid
extraction procedures (Parrish et aI., 1991; Christie, 1982).
Analysis of fatty acids in natural populations of freshwater algae are not common and are limited to cyanobacteria (Kenyon, 1972; Kenyon et a\., 1972) and
several species of green algae and flagellates (including dinoflagellates and
chrysophytes) (Cranwell et aI., 1990, 1988). Although diatoms are among the
major primary producers in freshwater ecosystems, their fatty acid compositions
have not been adequately studied. The fatty acid composition of natural and
laboratory algal populations can change dramatically as a function of environmental factors such as temperature, nutrient concentrations, and light (see Wainman et aI., this volume), and these variations are the consequence of a number of
interdependent factors affecting the cell cycle, lipid class composition, or membrane fluidity. Despite these adaptations to changing physiological and environmental conditions, there is a clear relationship between algal fatty acid
composition and taxa status. Table 2.1 presents examples of the fatty acid com-