Switching Between Deposit and Suspension Feeding in Coastal Zoobenthos
91
to facilitate intake by the siphon. In addition, Kamermans and Huitema (1994)
observed that the rotating behaviour was always carried out just prior to
ejecting pseudofaeces and considered it to be part of the deposit-feeding
behaviour.
4.3.1 Switching to Suspension Feeding
Different factors that control the choice between feeding on food particles
suspended in the water column or on food particles deposited on the sediment surface have been proposed for Macoma. These are:
l. High current velocities can cause drag on the siphons that prevents the
characteristic grazing movements of the siphon. This may lead to a switch
to suspension feeding (Levinton 1991; Peterson and Skilleter 1994).
2. High food availability in the water column compared to the surface of the
sediment may induce a switch to suspension feeding (Cadee 1984; Hummel
1985a; Olafsson 1986; Lin and Hines 1994).
3. High feeding on siphon tips by carnivorous bottom feeders such as fishes,
shrimps and crabs may cause a switch to suspension feeding in which the
siphons are not exposed above the sediment surface (Levinton 1971; de
VIas 1985; Kamermans and Huitema 1994; Skilleter and Peterson 1994).
4. High rates of lethal predation by birds and crabs may favour suspension
feeding. Burying deeply is important as protection against predation by
birds and crabs (Reading and McGrorty 1978; Blundon and Kennedy
1982). The length of the siphon determines the maximum depth at which
the animals can be buried in the sediment (Zwarts 1986). Zwarts and
Wan ink (1989) suggested that a feeding mode in which a short inhalant
siphon protrudes above the sediment may allow the bivalve to use the extra
length of the siphon to increase its burying depth.
The next sections discuss the data presented by the above-mentioned
authors to detect a possible switch to suspension feeding in Macoma. Before
doing so it is necessary to demonstrate that Macoma is capable of suspension
feeding. Kamermans (l994a) placed Macoma balthica on a grid and exposed
them to high concentrations of suspended algal cells only. The concentration
of algal cells was reduced compared to the control. The 4-week experiment
yielded growth rates that were higher than field rates. These results indicate
that Macoma is capable of suspension feeding. In addition, when food is not
limited, a suspension-feeding M. balthica can grow faster than M. balthica in
the field. However, the data presented in Table 4.1 show that this species can
not filter as efficiently as obligate suspension feeders. This observation suggests that suspension feeding is only utilised under suboptimal conditions
91
to facilitate intake by the siphon. In addition, Kamermans and Huitema (1994)
observed that the rotating behaviour was always carried out just prior to
ejecting pseudofaeces and considered it to be part of the deposit-feeding
behaviour.
4.3.1 Switching to Suspension Feeding
Different factors that control the choice between feeding on food particles
suspended in the water column or on food particles deposited on the sediment surface have been proposed for Macoma. These are:
l. High current velocities can cause drag on the siphons that prevents the
characteristic grazing movements of the siphon. This may lead to a switch
to suspension feeding (Levinton 1991; Peterson and Skilleter 1994).
2. High food availability in the water column compared to the surface of the
sediment may induce a switch to suspension feeding (Cadee 1984; Hummel
1985a; Olafsson 1986; Lin and Hines 1994).
3. High feeding on siphon tips by carnivorous bottom feeders such as fishes,
shrimps and crabs may cause a switch to suspension feeding in which the
siphons are not exposed above the sediment surface (Levinton 1971; de
VIas 1985; Kamermans and Huitema 1994; Skilleter and Peterson 1994).
4. High rates of lethal predation by birds and crabs may favour suspension
feeding. Burying deeply is important as protection against predation by
birds and crabs (Reading and McGrorty 1978; Blundon and Kennedy
1982). The length of the siphon determines the maximum depth at which
the animals can be buried in the sediment (Zwarts 1986). Zwarts and
Wan ink (1989) suggested that a feeding mode in which a short inhalant
siphon protrudes above the sediment may allow the bivalve to use the extra
length of the siphon to increase its burying depth.
The next sections discuss the data presented by the above-mentioned
authors to detect a possible switch to suspension feeding in Macoma. Before
doing so it is necessary to demonstrate that Macoma is capable of suspension
feeding. Kamermans (l994a) placed Macoma balthica on a grid and exposed
them to high concentrations of suspended algal cells only. The concentration
of algal cells was reduced compared to the control. The 4-week experiment
yielded growth rates that were higher than field rates. These results indicate
that Macoma is capable of suspension feeding. In addition, when food is not
limited, a suspension-feeding M. balthica can grow faster than M. balthica in
the field. However, the data presented in Table 4.1 show that this species can
not filter as efficiently as obligate suspension feeders. This observation suggests that suspension feeding is only utilised under suboptimal conditions