6. Seasonal Dynamics of Lipids
113
then transferred to their brooded eggs or young to provide them with energy
during their first few days of life. In addition, females with high lipid reserves may
be able to produce larger broods (Cavaletto et aI., 1996).
Lipid levels may also be important to the duration of the life cycle in Diporeia.
The length of the Diporeia life cycle increases with increasing depth. For example, in Lake Michigan, Diporeia has a I-year life cycle in the shelf region (l0-20
m), in the slope (30-90 m) it has a 2-year life cycle, and in the profundal zone
(>90 m) the life cycle is 2.5-3 years (Winnell and White, 1984). Food availability
and increased temperatures during the summer in the shelf region are probably
responsible for these varying life cycles; however, a certain lipid level may need
to be achieved before completion of the life cycle can occur in the different
regions (Hill et aI., 1992; Quigley et aI., 1989).
6.2.1.2. Mysidacea
Mysis relicta, commonly known as the opossum shrimp, usually inhabit deep,
cold, glacial lakes, although they can adapt to a wide range of environmental
conditions including temperatures up to 21 DC, low oxygen, and eutrophication
(Beeton and Gannon, 1991). Mysis usually inhabit depths >30 m, but in the Great
Lakes they may also be found in shallow regions when the lake is isothermal or
during upwelling events (Mozley and Howmiller, 1977). Mysis are considered to
be epibenthic because they spend the day in the sediments and migrate up into the
water column at night (Beeton, 1960). However, in deep regions of a lake (100 m)
mysids can occur 7 m above the sediments during the day (Beeton, 1960). Mysis
are omnivorous, feeding on detrital particles in sediments, algae, zooplankton,
and small Diporeia (Parker, 1980; Bowers and Grossnickle, 1978; Lasenby and
Langford, 1972). Mysis can take 1-4 years to reach sexual maturity, depending on
food availability (Adare and Lasenby, 1994; Morgan, 1980; Lasenby and
Langford, 1972) and temperature (Berrill and Lasenby, 1983). After a female
Mysis deposits her eggs in the marsupium and breeds with a male, she continues to
grow as the embryos and larvae develop. Following release of the young, the
female will usually die; however, in some instances Mysis have been documented
to produce a second brood (Morgan and Beeton, 1978).
Mysis from four Canadian lakes accumulated lipids as they matured. Life cycle
length depended on growth rate along with lipid accumulation rate and it varied in
the Mysis populations from the different lakes. For example, in the first 6 months
of life, Mysis with a 2-year life cycle grew at a rate of 1.0 mm . month -I and
accumulated 43.5 j.lg of lipid, whereas Mysis with a I-year life cycle grew 1.8
mm' month- I and accumulated 125 j.lg of lipid (Adare and Lasenby, 1994). On
maturity, Mysis attained their peak lipid levels in summer (Fig. 6.3). Maximum
mysid lipid levels ranged from 30 to 40% of dry mass in Canadian temperate lakes
(Adare and Lasenby, 1994). These levels are comparable with lipid levels of 33%
of dry mass for Lake Michigan Mysis (Fig. 6.4) (Gardner et aI., 1985a). TAG is the
most abundant lipid class (75.6% of total lipid) in Mysis from Lake Michigan
during late spring (Table 6.1).
113
then transferred to their brooded eggs or young to provide them with energy
during their first few days of life. In addition, females with high lipid reserves may
be able to produce larger broods (Cavaletto et aI., 1996).
Lipid levels may also be important to the duration of the life cycle in Diporeia.
The length of the Diporeia life cycle increases with increasing depth. For example, in Lake Michigan, Diporeia has a I-year life cycle in the shelf region (l0-20
m), in the slope (30-90 m) it has a 2-year life cycle, and in the profundal zone
(>90 m) the life cycle is 2.5-3 years (Winnell and White, 1984). Food availability
and increased temperatures during the summer in the shelf region are probably
responsible for these varying life cycles; however, a certain lipid level may need
to be achieved before completion of the life cycle can occur in the different
regions (Hill et aI., 1992; Quigley et aI., 1989).
6.2.1.2. Mysidacea
Mysis relicta, commonly known as the opossum shrimp, usually inhabit deep,
cold, glacial lakes, although they can adapt to a wide range of environmental
conditions including temperatures up to 21 DC, low oxygen, and eutrophication
(Beeton and Gannon, 1991). Mysis usually inhabit depths >30 m, but in the Great
Lakes they may also be found in shallow regions when the lake is isothermal or
during upwelling events (Mozley and Howmiller, 1977). Mysis are considered to
be epibenthic because they spend the day in the sediments and migrate up into the
water column at night (Beeton, 1960). However, in deep regions of a lake (100 m)
mysids can occur 7 m above the sediments during the day (Beeton, 1960). Mysis
are omnivorous, feeding on detrital particles in sediments, algae, zooplankton,
and small Diporeia (Parker, 1980; Bowers and Grossnickle, 1978; Lasenby and
Langford, 1972). Mysis can take 1-4 years to reach sexual maturity, depending on
food availability (Adare and Lasenby, 1994; Morgan, 1980; Lasenby and
Langford, 1972) and temperature (Berrill and Lasenby, 1983). After a female
Mysis deposits her eggs in the marsupium and breeds with a male, she continues to
grow as the embryos and larvae develop. Following release of the young, the
female will usually die; however, in some instances Mysis have been documented
to produce a second brood (Morgan and Beeton, 1978).
Mysis from four Canadian lakes accumulated lipids as they matured. Life cycle
length depended on growth rate along with lipid accumulation rate and it varied in
the Mysis populations from the different lakes. For example, in the first 6 months
of life, Mysis with a 2-year life cycle grew at a rate of 1.0 mm . month -I and
accumulated 43.5 j.lg of lipid, whereas Mysis with a I-year life cycle grew 1.8
mm' month- I and accumulated 125 j.lg of lipid (Adare and Lasenby, 1994). On
maturity, Mysis attained their peak lipid levels in summer (Fig. 6.3). Maximum
mysid lipid levels ranged from 30 to 40% of dry mass in Canadian temperate lakes
(Adare and Lasenby, 1994). These levels are comparable with lipid levels of 33%
of dry mass for Lake Michigan Mysis (Fig. 6.4) (Gardner et aI., 1985a). TAG is the
most abundant lipid class (75.6% of total lipid) in Mysis from Lake Michigan
during late spring (Table 6.1).