74
H. U. Riisgard and P. Kamermans
to discriminate between suspension feeders and deposit feeders because there
is a gradual transition from the food present in the top-layer of the sediment,
on which surface deposit feeders feed, to the suspended matter in the water
just above the sediment surface on which benthic suspension feeders feed.
This makes discrimination based on stomach content analysis alone doubtful.
In dynamically variable benthic environments organisms capable of
switching their feeding behaviour may be common. For example, a variety of
polychaetes representing some spionids, nereids, fabricine sabellids, and
oweniids possess such an ability to shift their feeding mode (Fauchald and
Jumars 1979). Buhr and Winter (1977) found that the polychaete Lanice conchilega is capable of replacing surface deposit feeding by suspension feeding
because the worm may retain suspended particles directly from the water
column by means of its tentacles. Switching feeding behaviour has been
reported in tellinids among the bivalves (Brafield and Newell 1961) and
amphipods among the crustaceans (Mills 1967; Fenchel et al. 1975; Taghon et
al. 1980). Thus, some benthic organisms appear versatile - 'opportunistic' - in
their feeding modes (Cadee 1984), but the relative significance of their
different feeding methods remains unclear. Furthermore, the ratio of suspension feeding to deposit feeding may vary considerably among different
populations of the same species. Switching from deposit to suspension feeding may be an adaptation particularly useful in shallow waters where the
concentration of suspended food particles may vary widely. Dauer et al.
(1981) used the term 'interface' feeders to refer to species that can switch between deposit and suspension feeding.
Zoobenthos live and feed on the sea floor in close contact with the
overlying water currents and resulting fluxes of particulate organic material.
Animals feeding upon this particulate material, as deposited or in nearbottom suspension, may be expected to respond to near-bottom currents and
sediment transport in their feeding behaviour (Miller et al. 1992). The development of additional, alternative suspension-feeding mechanisms among
various deposit-feeding zoobenthos is of primary importance when the
amount of available food is limited and when coexisting species compete for
food. The apparently widespread ability of deposit feeders to utilise alternative feeding mechanisms may lead to resource partitioning, and several
niche dimensions related to feeding may allow a certain diversity of coexisting species (Fenchel et al. 1975). The ability to use alternative feeding mechanisms thus seems to be an attribute of many deposit-feeding animals. This
paper attempts to give an outline of present knowledge about switching to
suspension feeding by deposit-feeding coastal zoobenthos.
H. U. Riisgard and P. Kamermans
to discriminate between suspension feeders and deposit feeders because there
is a gradual transition from the food present in the top-layer of the sediment,
on which surface deposit feeders feed, to the suspended matter in the water
just above the sediment surface on which benthic suspension feeders feed.
This makes discrimination based on stomach content analysis alone doubtful.
In dynamically variable benthic environments organisms capable of
switching their feeding behaviour may be common. For example, a variety of
polychaetes representing some spionids, nereids, fabricine sabellids, and
oweniids possess such an ability to shift their feeding mode (Fauchald and
Jumars 1979). Buhr and Winter (1977) found that the polychaete Lanice conchilega is capable of replacing surface deposit feeding by suspension feeding
because the worm may retain suspended particles directly from the water
column by means of its tentacles. Switching feeding behaviour has been
reported in tellinids among the bivalves (Brafield and Newell 1961) and
amphipods among the crustaceans (Mills 1967; Fenchel et al. 1975; Taghon et
al. 1980). Thus, some benthic organisms appear versatile - 'opportunistic' - in
their feeding modes (Cadee 1984), but the relative significance of their
different feeding methods remains unclear. Furthermore, the ratio of suspension feeding to deposit feeding may vary considerably among different
populations of the same species. Switching from deposit to suspension feeding may be an adaptation particularly useful in shallow waters where the
concentration of suspended food particles may vary widely. Dauer et al.
(1981) used the term 'interface' feeders to refer to species that can switch between deposit and suspension feeding.
Zoobenthos live and feed on the sea floor in close contact with the
overlying water currents and resulting fluxes of particulate organic material.
Animals feeding upon this particulate material, as deposited or in nearbottom suspension, may be expected to respond to near-bottom currents and
sediment transport in their feeding behaviour (Miller et al. 1992). The development of additional, alternative suspension-feeding mechanisms among
various deposit-feeding zoobenthos is of primary importance when the
amount of available food is limited and when coexisting species compete for
food. The apparently widespread ability of deposit feeders to utilise alternative feeding mechanisms may lead to resource partitioning, and several
niche dimensions related to feeding may allow a certain diversity of coexisting species (Fenchel et al. 1975). The ability to use alternative feeding mechanisms thus seems to be an attribute of many deposit-feeding animals. This
paper attempts to give an outline of present knowledge about switching to
suspension feeding by deposit-feeding coastal zoobenthos.