Switching Between Deposit and Suspension Feeding in Coastal Zoobenthos
75
4.1.1 Polychaetes
Polychaetes are among the most frequent and abundant marine invertebrates.
Fauchald and Jumars (1979) summarised the current information about food
and feeding habits of polychaetes, including predictions on the most likely
feeding habits in the form of hypotheses.
Arenicolids. Suspension feeding in arenicolids has for some time been a
controversial subject. Thus, the principal food source of the lugworm
Arenicola marina is still a point of contention. Generally, the lugworm is
regarded as a subsurface deposit feeder (see also Chap. 6) that is nourished by
swallowing relatively large amounts of sediments with low nutritional value.
A. marina lives in 20-40 em deep J-shaped burrows in the sediment. With its
head down, the worm ingests sediment. As a result the sand above sinks
downwards, forming a funnel. The pumping activity of the lugworm causes a
tail-to-head-directed ventilation current through its tube, resulting in an
upward flow of oxygenated water in the sediment in front of the head
(Riisgard et al.1996a; Riisgard and Banta 1998). It has been suggested that A.
marina may live as a suspension feeder by using the sand immediately in front
of the head as a particle-retaining filter for restraining suspended food particles in the water (Kruger 1959,1962,1964, 1971). Suspension-feeding macroinvertebrates are characterised by pumping large amounts of water per ml of
oxygen consumed. Thus, true filter-feeding macro-invertebrates (except for
sponges) pump 10 to 3501 of water per ml of oxygen consumed, which may be
compared with 0041 of water per ml of oxygen consumed in A. marina
(Table 4.1). This very low FIR-value means that the lugworm cannot survive as
a true suspension feeder. However, it does not exclude the possibility that
some fraction of its nutrition may come from suspended material drawn
down into the sediment while irrigating. Resuspended organic-rich sediment
may represent a potential food source, but subsurface deposit feeding must be
considered the major mode of feeding in the arenicolids (Riisgard and Banta
1998).
Chaetopterids. The suspension-feeding mode of the Chaetopteridae family is
well known. In all species a single or several mucus nets are used to capture
suspended food particles and the feeding current is set up by notopodial cilia
or muscular motion (Barnes 1964, 1965). However, at low particle concentrations, Spiochaetopterus sp. will search the sediment surface with the palps.
Thus, surface deposit feeding seems to be important for species living in
bathyal and abyssal regions, such as Spiochaetopterus costarum and Phyllochaetopterus limnicolus in the Pacific Ocean (Fauchald and Jumars 1979). In P.
prolifica two feeding modes other than the mucus filter-bag feeding method
75
4.1.1 Polychaetes
Polychaetes are among the most frequent and abundant marine invertebrates.
Fauchald and Jumars (1979) summarised the current information about food
and feeding habits of polychaetes, including predictions on the most likely
feeding habits in the form of hypotheses.
Arenicolids. Suspension feeding in arenicolids has for some time been a
controversial subject. Thus, the principal food source of the lugworm
Arenicola marina is still a point of contention. Generally, the lugworm is
regarded as a subsurface deposit feeder (see also Chap. 6) that is nourished by
swallowing relatively large amounts of sediments with low nutritional value.
A. marina lives in 20-40 em deep J-shaped burrows in the sediment. With its
head down, the worm ingests sediment. As a result the sand above sinks
downwards, forming a funnel. The pumping activity of the lugworm causes a
tail-to-head-directed ventilation current through its tube, resulting in an
upward flow of oxygenated water in the sediment in front of the head
(Riisgard et al.1996a; Riisgard and Banta 1998). It has been suggested that A.
marina may live as a suspension feeder by using the sand immediately in front
of the head as a particle-retaining filter for restraining suspended food particles in the water (Kruger 1959,1962,1964, 1971). Suspension-feeding macroinvertebrates are characterised by pumping large amounts of water per ml of
oxygen consumed. Thus, true filter-feeding macro-invertebrates (except for
sponges) pump 10 to 3501 of water per ml of oxygen consumed, which may be
compared with 0041 of water per ml of oxygen consumed in A. marina
(Table 4.1). This very low FIR-value means that the lugworm cannot survive as
a true suspension feeder. However, it does not exclude the possibility that
some fraction of its nutrition may come from suspended material drawn
down into the sediment while irrigating. Resuspended organic-rich sediment
may represent a potential food source, but subsurface deposit feeding must be
considered the major mode of feeding in the arenicolids (Riisgard and Banta
1998).
Chaetopterids. The suspension-feeding mode of the Chaetopteridae family is
well known. In all species a single or several mucus nets are used to capture
suspended food particles and the feeding current is set up by notopodial cilia
or muscular motion (Barnes 1964, 1965). However, at low particle concentrations, Spiochaetopterus sp. will search the sediment surface with the palps.
Thus, surface deposit feeding seems to be important for species living in
bathyal and abyssal regions, such as Spiochaetopterus costarum and Phyllochaetopterus limnicolus in the Pacific Ocean (Fauchald and Jumars 1979). In P.
prolifica two feeding modes other than the mucus filter-bag feeding method