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J.F. Cavaletto and W.S. Gardner
tion indicated no occurrence of a seasonal algal event. However, FA analysis did
reveal an unsaturated FA ratio typical of terrestrial plants. Therefore, it appears
that land-based detrital material is an important component of the diet of D.
patagonicus (Pollero and Brenner, 1981; Pollero et aI., 1981 b). In addition, reproduction appeared to influence lipid composition of a related species, Diplodon
delodontus (Pollero et al.. 1983). For example. TAG levels of D. delodontus
increased in both sexes prior to gametogenesis, although TAG levels were higher
in females than in males. Furthermore, specific unsaturated FAs also increased
with the maturing of the oocytes. Like other benthic invertebrates. lipid production in the spring is important for Diplodon spp. to successfully reproduce.
Zebra mussels (Dreissena polymorpha) invaded the lakes and rivers of central
Europe at the beginning of the past century. In the late 1980s, Dreissena invaded
the Great Lakes ecosystem (Hebert et aI., 1989) and continue to spread into water
bodies across the south and to the west in North America. Dreissena are nuisance
organisms due to their mode of attachment and rapid colonization of hard surfaces. We are only beginning to understand the cascading effects that result from
the invasion of this exotic species. For example, dreissenids alter native ecosystems due to their tremendous ability to filter phytoplankton from the water
(Fanslow et al.. 1995) and shift the main use of primary production from the
pelagic zone to the benthos (Lowe and Pillsbury. 1995). Many studies have been
done to try to better understand and possibly help control the spread of Dreissena
(Nalepa and Fahnenstiel, 1995; Nalepa and Schloesser, 1993).
Dreissena are short lived for mollusks (3-4 years), but they still produce many
offspring. Unlike most freshwater bivalves that have a parasitic larval stage,
Dreissena has a free-swimming veliger larva like marine bivalves (Sprung, 1989).
Dreissena mature rather fast and begin to produce gametes when they are approximately 8 mm in length; they may increase the number of gametes produced as
they grow (Sprung, 1991).
Biochemical composition of Dreissena soft tissues has been examined in several studies in relation to growth, reproduction, and starvation under natural
and experimental conditions (Sprung, 1995; Nalepa et al.. 1993; Sprung and
Borcherding, 1991; Walz, 1979). Dreissena are unusual bivalves whose major
energy reserve appears to be lipid rather than glycogen (Sprung, 1995; Sprung and
Borcherding, 1991). Lipid content of Dreissena varies seasonally (Fig. 6.5).
Dreissena total lipid was usually highest in the spring and declined throughout the
summer and fall. although this may vary with food availability (Sprung. 1995;
Nalepa et al.. 1993). Lipid is concentrated in the digestive gland of Dreissena, and
on proper conditions for reproduction (i.e., mainly a temperature of 12°C or
greater), some lipid is transferred from the digestive gland to the gonad (Sprung,
1995). Like most freshwater organisms, Dreissena storage lipid is TAG. Their
TAG concentration peaks in the spring and then declines throughout the remaining seasons (Fig. 6.6) (Nalepa et aI., 1993). Structural membrane component lipid
(i.e., PL) remains relatively stable from spring until fall and is most often the main
lipid class in zebra mussels (Fig. 6.6; Table 6.1).
J.F. Cavaletto and W.S. Gardner
tion indicated no occurrence of a seasonal algal event. However, FA analysis did
reveal an unsaturated FA ratio typical of terrestrial plants. Therefore, it appears
that land-based detrital material is an important component of the diet of D.
patagonicus (Pollero and Brenner, 1981; Pollero et aI., 1981 b). In addition, reproduction appeared to influence lipid composition of a related species, Diplodon
delodontus (Pollero et al.. 1983). For example. TAG levels of D. delodontus
increased in both sexes prior to gametogenesis, although TAG levels were higher
in females than in males. Furthermore, specific unsaturated FAs also increased
with the maturing of the oocytes. Like other benthic invertebrates. lipid production in the spring is important for Diplodon spp. to successfully reproduce.
Zebra mussels (Dreissena polymorpha) invaded the lakes and rivers of central
Europe at the beginning of the past century. In the late 1980s, Dreissena invaded
the Great Lakes ecosystem (Hebert et aI., 1989) and continue to spread into water
bodies across the south and to the west in North America. Dreissena are nuisance
organisms due to their mode of attachment and rapid colonization of hard surfaces. We are only beginning to understand the cascading effects that result from
the invasion of this exotic species. For example, dreissenids alter native ecosystems due to their tremendous ability to filter phytoplankton from the water
(Fanslow et al.. 1995) and shift the main use of primary production from the
pelagic zone to the benthos (Lowe and Pillsbury. 1995). Many studies have been
done to try to better understand and possibly help control the spread of Dreissena
(Nalepa and Fahnenstiel, 1995; Nalepa and Schloesser, 1993).
Dreissena are short lived for mollusks (3-4 years), but they still produce many
offspring. Unlike most freshwater bivalves that have a parasitic larval stage,
Dreissena has a free-swimming veliger larva like marine bivalves (Sprung, 1989).
Dreissena mature rather fast and begin to produce gametes when they are approximately 8 mm in length; they may increase the number of gametes produced as
they grow (Sprung, 1991).
Biochemical composition of Dreissena soft tissues has been examined in several studies in relation to growth, reproduction, and starvation under natural
and experimental conditions (Sprung, 1995; Nalepa et al.. 1993; Sprung and
Borcherding, 1991; Walz, 1979). Dreissena are unusual bivalves whose major
energy reserve appears to be lipid rather than glycogen (Sprung, 1995; Sprung and
Borcherding, 1991). Lipid content of Dreissena varies seasonally (Fig. 6.5).
Dreissena total lipid was usually highest in the spring and declined throughout the
summer and fall. although this may vary with food availability (Sprung. 1995;
Nalepa et al.. 1993). Lipid is concentrated in the digestive gland of Dreissena, and
on proper conditions for reproduction (i.e., mainly a temperature of 12°C or
greater), some lipid is transferred from the digestive gland to the gonad (Sprung,
1995). Like most freshwater organisms, Dreissena storage lipid is TAG. Their
TAG concentration peaks in the spring and then declines throughout the remaining seasons (Fig. 6.6) (Nalepa et aI., 1993). Structural membrane component lipid
(i.e., PL) remains relatively stable from spring until fall and is most often the main
lipid class in zebra mussels (Fig. 6.6; Table 6.1).