88
H.U. Riisgard and P. Kamermans
pumping rate was expressed as: Q=Qp -Q u where Qp=volume flow of a leakfree pump and QL=volume flow of leakage. In the expression, Qp=ALf, A, L
and f denote piston area, stroke length and stroke frequency of the pumping
action, respectively.
The engineering principles of pump analysis and modelling of Nereis
diversicolor and other suspension-feeding macroinvertebrates have been reviewed by Riisgard and Larsen (1995). Only the energy cost of pumping will
briefly be mentioned here. The useful pumping power ('power output') of the
Nereis pump was calculated as the product of pump pressure and pumping
rate to be P=2.10 JlW. The total metabolic rate of the worm was measured at
R=12.6 JlI 02 h- 1 , equivalent to 70 JlW, and the overall pump efficiency ('pump
work') was estimated to be P/R=3 % of the total metabolic energy expenditure. This low value is comparable with the obligate suspension-feeding
polychaete Chaetopterus variopedatus (Riisgard 1989) and other true suspension-feeding macroinvertebrates (Riisgard and Larsen 1995).
4.2.5 Adaptation to Suspension Feeding
To obtain enough food to satiate the minimal energy requirements the performance of suspension feeders inhabiting inshore waters must generally
exceed 10 I of water per ml of oxygen consumed (J0rgensen 1975). From this
reference, and with a thorough knowledge of particle retention efficiency, the
adaptation of suspension feeders to different biotopes with different typical
phytoplankton levels may be evaluated and compared. By relating the pumping rates to respiration, Riisgard (1991) found that N. diversicolor pumps
approximately 40 I of water per ml oxygen consumed. This shows that N.
diversicolor fulfils the conditions for subsistance exclusively as a filter feeder,
provided that the phytoplankton concentration is sufficiently high. But this is
not always the case. It is therefore of interest to know how much time N.
diversicolor spends on filter feeding versus surface deposit feeding, or other
alternative foraging forms.
4.2.6 Time Spent on Suspension Feeding
To investigate to what extent suspension feeding of Nereis diversicolor in the
field varies over the season, Vedel et al. (1993, 1994) and Vedel (1998) used an
infrared phototransducer system to obtain continuous, long-term measurements of the characteristic undulating body movements of the filter-feeding
activity of N. diversicolor in glass tubes immersed in the natural sediment.
The phototransducer system consists of an infrared light-emitting diode and
a photo transistor detector. The photo transistor detected variations in reflec-
H.U. Riisgard and P. Kamermans
pumping rate was expressed as: Q=Qp -Q u where Qp=volume flow of a leakfree pump and QL=volume flow of leakage. In the expression, Qp=ALf, A, L
and f denote piston area, stroke length and stroke frequency of the pumping
action, respectively.
The engineering principles of pump analysis and modelling of Nereis
diversicolor and other suspension-feeding macroinvertebrates have been reviewed by Riisgard and Larsen (1995). Only the energy cost of pumping will
briefly be mentioned here. The useful pumping power ('power output') of the
Nereis pump was calculated as the product of pump pressure and pumping
rate to be P=2.10 JlW. The total metabolic rate of the worm was measured at
R=12.6 JlI 02 h- 1 , equivalent to 70 JlW, and the overall pump efficiency ('pump
work') was estimated to be P/R=3 % of the total metabolic energy expenditure. This low value is comparable with the obligate suspension-feeding
polychaete Chaetopterus variopedatus (Riisgard 1989) and other true suspension-feeding macroinvertebrates (Riisgard and Larsen 1995).
4.2.5 Adaptation to Suspension Feeding
To obtain enough food to satiate the minimal energy requirements the performance of suspension feeders inhabiting inshore waters must generally
exceed 10 I of water per ml of oxygen consumed (J0rgensen 1975). From this
reference, and with a thorough knowledge of particle retention efficiency, the
adaptation of suspension feeders to different biotopes with different typical
phytoplankton levels may be evaluated and compared. By relating the pumping rates to respiration, Riisgard (1991) found that N. diversicolor pumps
approximately 40 I of water per ml oxygen consumed. This shows that N.
diversicolor fulfils the conditions for subsistance exclusively as a filter feeder,
provided that the phytoplankton concentration is sufficiently high. But this is
not always the case. It is therefore of interest to know how much time N.
diversicolor spends on filter feeding versus surface deposit feeding, or other
alternative foraging forms.
4.2.6 Time Spent on Suspension Feeding
To investigate to what extent suspension feeding of Nereis diversicolor in the
field varies over the season, Vedel et al. (1993, 1994) and Vedel (1998) used an
infrared phototransducer system to obtain continuous, long-term measurements of the characteristic undulating body movements of the filter-feeding
activity of N. diversicolor in glass tubes immersed in the natural sediment.
The phototransducer system consists of an infrared light-emitting diode and
a photo transistor detector. The photo transistor detected variations in reflec-