5
Lipid Dietary Dependencies
in Zooplankton
Clyde E. Goulden, Robert E. Moeller, James N. McNair, and
Allen R. Place
5.1. Introduction
Zooplankton accumulate large amounts of lipids, as much as 40-70% of the dry
mass of their body (Goulden and Henry, 1985; Lee et aI., 1972). Some polyunsaturated fatty acids and sterols are essential but required in trace amounts. By
contrast, storage and membrane lipids are generally composed of nonessential
lipids and make up an important energy reserve.
The known essential fatty acids (EFA) of zooplankton and other metazoans
appear to be linoleic, 18:2(06 and linolenic, 18:3(03 acids (Conklin and Provasoli,
1977) and perhaps the polyunsaturated fatty acid, eicosapentaenoic acid (EPA;
20:5(03). However, studies of animals exposed to controlled diets lacking EPA
for multiple generations have not been performed. This approach would demonstrate the essential need of EPA for many metazoans. Experimental studies by
D' Abramo (1979) suggest that the absence or low concentrations of this polyunsaturated fatty acid may affect clutch sizes and the rate of reproduction in the
cladoceran Moina. Some sterols, particularly cholesterol, are essential to all crustaceans, although little has been done to study them in zooplankton.
Lipids also playa vital role in the ecology of zooplankton. Storage lipids, such
as triacylglycerols (TAG) and wax esters, do represent the primary source of
metabolic energy in copepods and Cladocera during periods of low ambient food
levels (Goulden and Henry, 1985; Lee et aI., 1972). Lipids are also extremely
important in egg yolk, again serving as a major part of the metabolic energy of
developing embryos and neonates (Goulden et aI., 1987).
Although it is known that lipids are critical to survival of zooplankton, many
questions remain to explain this observation within the context of the animal's
ecology. For example, do the large amounts of lipid accumulated by zooplankton
originate from the diet directly as lipid (or fatty acids), or are they biosynthesized
by the animals? If accumulated directly from the diet, are there sufficient lipids in
natural zooplankton diets to support this large dependency?
The purpose of this research has been to determine whether "food limitations"
may stem from deficiencies of particular food components, either as single essential compounds or as groups of compounds such as lipids. An understanding of
91
Lipid Dietary Dependencies
in Zooplankton
Clyde E. Goulden, Robert E. Moeller, James N. McNair, and
Allen R. Place
5.1. Introduction
Zooplankton accumulate large amounts of lipids, as much as 40-70% of the dry
mass of their body (Goulden and Henry, 1985; Lee et aI., 1972). Some polyunsaturated fatty acids and sterols are essential but required in trace amounts. By
contrast, storage and membrane lipids are generally composed of nonessential
lipids and make up an important energy reserve.
The known essential fatty acids (EFA) of zooplankton and other metazoans
appear to be linoleic, 18:2(06 and linolenic, 18:3(03 acids (Conklin and Provasoli,
1977) and perhaps the polyunsaturated fatty acid, eicosapentaenoic acid (EPA;
20:5(03). However, studies of animals exposed to controlled diets lacking EPA
for multiple generations have not been performed. This approach would demonstrate the essential need of EPA for many metazoans. Experimental studies by
D' Abramo (1979) suggest that the absence or low concentrations of this polyunsaturated fatty acid may affect clutch sizes and the rate of reproduction in the
cladoceran Moina. Some sterols, particularly cholesterol, are essential to all crustaceans, although little has been done to study them in zooplankton.
Lipids also playa vital role in the ecology of zooplankton. Storage lipids, such
as triacylglycerols (TAG) and wax esters, do represent the primary source of
metabolic energy in copepods and Cladocera during periods of low ambient food
levels (Goulden and Henry, 1985; Lee et aI., 1972). Lipids are also extremely
important in egg yolk, again serving as a major part of the metabolic energy of
developing embryos and neonates (Goulden et aI., 1987).
Although it is known that lipids are critical to survival of zooplankton, many
questions remain to explain this observation within the context of the animal's
ecology. For example, do the large amounts of lipid accumulated by zooplankton
originate from the diet directly as lipid (or fatty acids), or are they biosynthesized
by the animals? If accumulated directly from the diet, are there sufficient lipids in
natural zooplankton diets to support this large dependency?
The purpose of this research has been to determine whether "food limitations"
may stem from deficiencies of particular food components, either as single essential compounds or as groups of compounds such as lipids. An understanding of
91