6. Seasonal Dynamics of Lipids
117
6.2.2. Shelf and Nearshore Zones
6.2.2.1. Crustacea: Amphipoda
Unlike Diporeia, the majority of freshwater amphipods inhabit nearshore areas of
lakes, ponds, and streams, and they usually live in and around vegetation from the
surface to 1 m deep (Pennak, 1978). Seasonal variation in lipid content was
determined in two common species of amphipods, Byalella azteca and Gammarus lacustris, in conjunction with a contaminant study (Arts et aI., 1995).
Amphipods were analyzed from three Canadian prairie lakes that are in the
vicinity of agricultural herbicide applications.
In H. azteca, lipid levels ranged from 2.5 to 16.3% of dry mass and varied
seasonally in two of three lakes. In both of these lakes, lipid levels were highest in
spring and declined through the summer, with lipid levels increasing again in
autumn in H. azteca from one of the lakes. In addition, females usually had higher
lipid levels than males in spring and early summer during reproduction (Arts et aI.,
1995). Similarly, total lipid levels in H. azteca from a Michigan pond were 17.4%
± 3.7 (SE) of dry mass in autumn (Cavaletto and Gardner, unpublished data). In
G. lacustris, lipid levels ranged from 2.4 to 15.7% of dry mass. Like H. azteca,
lipid levels in G. lacustris were highest, especially in females, during the reproductive period in spring and early summer (Arts et aI., 1995). TAG was the
most abundant lipid class in both H. azteca and G. lacustris, ranging from 22.6 to
67.3% of total lipid. In addition, the contaminant studied (i.e., triallate) was
positively correlated with TAG in both amphipods (Arts et aI., 1995).
6.2.2.2. Annelida: Oligochaeta
Oligochaete worms are the most abundant benthic macroinvertebrates in many
shallow bays, harbors, and river mouths, and they occur from nearshore areas to
the profundal zone (Schloesser et aI., 1995; Brinkhurst, 1970, 1967). Many species of oligochaetes are used as water-quality indicators. For example, high densities of Tubifex tubifex or Limnodrilus hoffmeisteri are usually found in polluted
environments. The presence of Stylodrilus heringianus is an indication of oligotrophic conditions, and they are more commonly found in the profundal zone of
lakes (Nalepa, 1991; Mozley and Howmiller, 1977). Benthic oligochaetes usually
feed with their anterior ends 4-6 cm below the sediment-water interface and
defecate at the sediment surface (Appleby and Brinkhurst, 1970). Oligochaetes
are continuous feeders and derive nutrition from the detritus and bacteria present
in the sediment (Wavre and Brinkhurst, 1971; Brinkhurst and Chua, 1969). Lipids
have been studied in oligochaetes from the family Tubificidae and S. herigianus
(Lumbriculidae) (Gardner et aI., 1985a). These oligochaetes had no apparent
seasonal lipid pattern; however, total lipids varied between 8-20% of dry mass
(Fig. 6.4).
Phospholipids (PL) are the most abundant lipid class in tubificids. Oligochaetes
have large surface areas of unprotected epidermis (no carapace or cuticle) that
require a high portion of structural membrane PL. Sterol (ST; most commonly
117
6.2.2. Shelf and Nearshore Zones
6.2.2.1. Crustacea: Amphipoda
Unlike Diporeia, the majority of freshwater amphipods inhabit nearshore areas of
lakes, ponds, and streams, and they usually live in and around vegetation from the
surface to 1 m deep (Pennak, 1978). Seasonal variation in lipid content was
determined in two common species of amphipods, Byalella azteca and Gammarus lacustris, in conjunction with a contaminant study (Arts et aI., 1995).
Amphipods were analyzed from three Canadian prairie lakes that are in the
vicinity of agricultural herbicide applications.
In H. azteca, lipid levels ranged from 2.5 to 16.3% of dry mass and varied
seasonally in two of three lakes. In both of these lakes, lipid levels were highest in
spring and declined through the summer, with lipid levels increasing again in
autumn in H. azteca from one of the lakes. In addition, females usually had higher
lipid levels than males in spring and early summer during reproduction (Arts et aI.,
1995). Similarly, total lipid levels in H. azteca from a Michigan pond were 17.4%
± 3.7 (SE) of dry mass in autumn (Cavaletto and Gardner, unpublished data). In
G. lacustris, lipid levels ranged from 2.4 to 15.7% of dry mass. Like H. azteca,
lipid levels in G. lacustris were highest, especially in females, during the reproductive period in spring and early summer (Arts et aI., 1995). TAG was the
most abundant lipid class in both H. azteca and G. lacustris, ranging from 22.6 to
67.3% of total lipid. In addition, the contaminant studied (i.e., triallate) was
positively correlated with TAG in both amphipods (Arts et aI., 1995).
6.2.2.2. Annelida: Oligochaeta
Oligochaete worms are the most abundant benthic macroinvertebrates in many
shallow bays, harbors, and river mouths, and they occur from nearshore areas to
the profundal zone (Schloesser et aI., 1995; Brinkhurst, 1970, 1967). Many species of oligochaetes are used as water-quality indicators. For example, high densities of Tubifex tubifex or Limnodrilus hoffmeisteri are usually found in polluted
environments. The presence of Stylodrilus heringianus is an indication of oligotrophic conditions, and they are more commonly found in the profundal zone of
lakes (Nalepa, 1991; Mozley and Howmiller, 1977). Benthic oligochaetes usually
feed with their anterior ends 4-6 cm below the sediment-water interface and
defecate at the sediment surface (Appleby and Brinkhurst, 1970). Oligochaetes
are continuous feeders and derive nutrition from the detritus and bacteria present
in the sediment (Wavre and Brinkhurst, 1971; Brinkhurst and Chua, 1969). Lipids
have been studied in oligochaetes from the family Tubificidae and S. herigianus
(Lumbriculidae) (Gardner et aI., 1985a). These oligochaetes had no apparent
seasonal lipid pattern; however, total lipids varied between 8-20% of dry mass
(Fig. 6.4).
Phospholipids (PL) are the most abundant lipid class in tubificids. Oligochaetes
have large surface areas of unprotected epidermis (no carapace or cuticle) that
require a high portion of structural membrane PL. Sterol (ST; most commonly