80
H. U. Riisgard and P. Kamermans
help of its palps, or it can feed on surface deposits (Hempel 1957). Supplementary suspension feeding may take place in most species, but it is difficult to
distinguish from feeding on resuspended bottom materials. Taghon et al.
(1980) reported on a novel suspension-feeding mechanism in three species of
spionid polychaetes (Pseudopolydora kempi japonica, Boccardia proboscidea,
P. elegans). It was found that the feeding behaviour of these spionids varied
with the water velocity. At moderate flows the worms cease deposit feeding
and form their feeding tentacles into helices that are lifted into the water and
extended downstream to capture material in suspension. This behaviour is
apparently a response to increased flux of suspended matter rather than to
water current velocity alone. Brine shrimps introduced upstream were
captured along the entire length of the tentacles and transported to the mouth
by ciliary action. Direct interception by the tentacle is the primary means by
which these annelids feed on larger particles in suspension (for detailed
description of 'direct interception' capture mechanisms, see Shimeta and
Jumars 1991). Miller et al. (1992) reported that the spionid Spio setosa is a
deposit feeder in still water, but a facultative, palp-coiling suspension feeder
in oscillatory flows. Taghon and Greene (1992) tested the hypothesis that
switching from deposit feeding to suspension feeding in P. kempi japonica
and B. pugettensis as the flux of suspended particles increases is energetically
profitable because suspended particles have greater food value.
Terebellids. Lanice conchilega feeds on material in bed-load transport.
Laboratory experiments carried out by Buhr (1976) revealed that, in addition
to surface deposit feeding, suspension feeding may playa role in the nutrition
of this polychaete. The anterior end of the worm is equipped with a series of
extensible tentacles that are oriented at right angles to the current. This
orientation makes them function as baffles in the current, allowing transported material to drop in the quiet areas behind the fans. The feeding
behaviour of L. conchilega has been discussed by Buhr and Winter (1977).
From the high population densities observed in the outer part of the Weser
Estuary, Germany, they found it unlikely that L. conchilega engages solely in
surface deposit feeding. The fringed ends of the tubes of populations in this
habitat form a dense network, such that only a limited amount of detritus
reaches the bottom. Consequently, food requirements have to be fulfilled by
an alternative. Food uptake may thus be performed not only from the bottom
surface, but also from the fringed ends of the tubes.
4.1.2 Echinoderms
The brittle-star Amphiura filiformis feeds on suspended material in flowing
water, but shifts to deposit feeding in stagnant water (Loo et al. 1996). In still
H. U. Riisgard and P. Kamermans
help of its palps, or it can feed on surface deposits (Hempel 1957). Supplementary suspension feeding may take place in most species, but it is difficult to
distinguish from feeding on resuspended bottom materials. Taghon et al.
(1980) reported on a novel suspension-feeding mechanism in three species of
spionid polychaetes (Pseudopolydora kempi japonica, Boccardia proboscidea,
P. elegans). It was found that the feeding behaviour of these spionids varied
with the water velocity. At moderate flows the worms cease deposit feeding
and form their feeding tentacles into helices that are lifted into the water and
extended downstream to capture material in suspension. This behaviour is
apparently a response to increased flux of suspended matter rather than to
water current velocity alone. Brine shrimps introduced upstream were
captured along the entire length of the tentacles and transported to the mouth
by ciliary action. Direct interception by the tentacle is the primary means by
which these annelids feed on larger particles in suspension (for detailed
description of 'direct interception' capture mechanisms, see Shimeta and
Jumars 1991). Miller et al. (1992) reported that the spionid Spio setosa is a
deposit feeder in still water, but a facultative, palp-coiling suspension feeder
in oscillatory flows. Taghon and Greene (1992) tested the hypothesis that
switching from deposit feeding to suspension feeding in P. kempi japonica
and B. pugettensis as the flux of suspended particles increases is energetically
profitable because suspended particles have greater food value.
Terebellids. Lanice conchilega feeds on material in bed-load transport.
Laboratory experiments carried out by Buhr (1976) revealed that, in addition
to surface deposit feeding, suspension feeding may playa role in the nutrition
of this polychaete. The anterior end of the worm is equipped with a series of
extensible tentacles that are oriented at right angles to the current. This
orientation makes them function as baffles in the current, allowing transported material to drop in the quiet areas behind the fans. The feeding
behaviour of L. conchilega has been discussed by Buhr and Winter (1977).
From the high population densities observed in the outer part of the Weser
Estuary, Germany, they found it unlikely that L. conchilega engages solely in
surface deposit feeding. The fringed ends of the tubes of populations in this
habitat form a dense network, such that only a limited amount of detritus
reaches the bottom. Consequently, food requirements have to be fulfilled by
an alternative. Food uptake may thus be performed not only from the bottom
surface, but also from the fringed ends of the tubes.
4.1.2 Echinoderms
The brittle-star Amphiura filiformis feeds on suspended material in flowing
water, but shifts to deposit feeding in stagnant water (Loo et al. 1996). In still