THE DEEP-SEA FLOOR: AN OVERVIEW
21
but not for active suspension feeders. Therefore, the
number of suitable locations (and therefore abundance)
should decrease more rapidly with depth for active
suspension feeders than for passive suspension feeders.
This pattern has been observed (Jumars and Gallagher,
1982).
Given the low suspended-particle concentrations in
the deep sea, maximizing the particle-capture rate may
be particularly important. In particular, passive suspension feeders should orient their collecting surfaces to
maximize the flux of particles that they intercept. Data
from the deep sea with which to test this prediction
are sparse, but some types of behavior are suggestive.
For example, the sea anemone Sicyonis tuberculata
bends its body in such a way that its feeding surface
faces into the current as the current direction rotates
with the tide (Lampitt and Paterson, 1987). Also, under
the West-African upwelling, the vertical flux of food
particles is large and near-bottom currents are slow, so
the vertical flux of food particles greatly exceeds the
horizontal flux. There, the passive suspension-feeding
sea anemone Actinoscyphia aurelia orients its collector
upwards, as expected (Aldred et al., 1979).
Some passive suspension feeders increase particle
capture rates by exploiting the increase in horizontal
speed of the near-bottom water as distance from
the seabed increases. For example, the deep-sea
foraminifer Miliolinella subrotunda builds a pedestal
1–6 mm tall on which it perches to suspension-feed
(Altenbach et al., 1993). Other passive suspension
feeders occur on topographic features or the stalks of
other organisms, such as glass sponges, thus placing
their feeding apparatus in regions of more rapid flow.
A sea anemone moved ~30 cm up the side of an
experimental cage in ~5 days to perch at the highest
point (personal observation).
Some shallow-water polychaetes can switch feeding
modes (Taghon et al., 1980; Dauer et al., 1981).
When the flux of suspended particles is large enough,
these species suspension-feed. When it is not, they
deposit-feed. Many deep-sea polychaetes are thought to
have this capability (G. Paterson, personal communication, 1997).
Carnivores/predators
Carnivores select and consume living prey. For
example, in the deep sea, kinorhynchs have been found
with their heads embedded in the sides of nematodes
(personal observation). Such direct evidence of feeding
on live prey is difficult to obtain from the deep sea.
Gut-content analysis, both by visual inspection (Langer
et al., 1995) and by immunological methods (Feller
et al., 1985), has been used; but this approach cannot
always distinguish carnivores from scavengers. As a
result, feeding mode is often inferred from the feeding
patterns of similar, shallow-water species. For example,
a group of deep-sea nematodes with teeth in their
buccal cavities (Fig. 2.16) are thought to be carnivores
because shallow-water species with such armature are
carnivorous (Jensen, 1992). The proportion of the
deep-sea fauna that is carnivorous is not well known.
Jumars and Gallagher (1982) estimated that carnivores
constituted between 2% and 13% of the polychaetes
at four Pacific sites. Tselepides and Eleftheriou (1992)
reported that 49–52% of the polychaetes between 700
and 1000 m depth off Crete were carnivorous.
Fig. 2.16. Examples of deep-sea nematodes that are thought to be
carnivores because their buccal cavities have teeth as do carnivorous
nematodes in shallow water. Only the anterior portion of each worm
is shown. Modified from Jensen (1992). Reproduced by permission
of the Station Biologique de Roscoff.
In the food-poor deep sea, prey are rare, so the time
between encounters with prey will be long compared
to that needed to subdue and ingest a prey item
once encountered. Under these circumstances, optimalforaging theory predicts that diets should be generalized to shorten the time between prey encounters,
increasing the food-acquisition rate (MacArthur, 1972).
The step from feeding on live prey to including carrion
in the diet is a small one, so organisms that might be
predators in shallow water are likely to consume both
21
but not for active suspension feeders. Therefore, the
number of suitable locations (and therefore abundance)
should decrease more rapidly with depth for active
suspension feeders than for passive suspension feeders.
This pattern has been observed (Jumars and Gallagher,
1982).
Given the low suspended-particle concentrations in
the deep sea, maximizing the particle-capture rate may
be particularly important. In particular, passive suspension feeders should orient their collecting surfaces to
maximize the flux of particles that they intercept. Data
from the deep sea with which to test this prediction
are sparse, but some types of behavior are suggestive.
For example, the sea anemone Sicyonis tuberculata
bends its body in such a way that its feeding surface
faces into the current as the current direction rotates
with the tide (Lampitt and Paterson, 1987). Also, under
the West-African upwelling, the vertical flux of food
particles is large and near-bottom currents are slow, so
the vertical flux of food particles greatly exceeds the
horizontal flux. There, the passive suspension-feeding
sea anemone Actinoscyphia aurelia orients its collector
upwards, as expected (Aldred et al., 1979).
Some passive suspension feeders increase particle
capture rates by exploiting the increase in horizontal
speed of the near-bottom water as distance from
the seabed increases. For example, the deep-sea
foraminifer Miliolinella subrotunda builds a pedestal
1–6 mm tall on which it perches to suspension-feed
(Altenbach et al., 1993). Other passive suspension
feeders occur on topographic features or the stalks of
other organisms, such as glass sponges, thus placing
their feeding apparatus in regions of more rapid flow.
A sea anemone moved ~30 cm up the side of an
experimental cage in ~5 days to perch at the highest
point (personal observation).
Some shallow-water polychaetes can switch feeding
modes (Taghon et al., 1980; Dauer et al., 1981).
When the flux of suspended particles is large enough,
these species suspension-feed. When it is not, they
deposit-feed. Many deep-sea polychaetes are thought to
have this capability (G. Paterson, personal communication, 1997).
Carnivores/predators
Carnivores select and consume living prey. For
example, in the deep sea, kinorhynchs have been found
with their heads embedded in the sides of nematodes
(personal observation). Such direct evidence of feeding
on live prey is difficult to obtain from the deep sea.
Gut-content analysis, both by visual inspection (Langer
et al., 1995) and by immunological methods (Feller
et al., 1985), has been used; but this approach cannot
always distinguish carnivores from scavengers. As a
result, feeding mode is often inferred from the feeding
patterns of similar, shallow-water species. For example,
a group of deep-sea nematodes with teeth in their
buccal cavities (Fig. 2.16) are thought to be carnivores
because shallow-water species with such armature are
carnivorous (Jensen, 1992). The proportion of the
deep-sea fauna that is carnivorous is not well known.
Jumars and Gallagher (1982) estimated that carnivores
constituted between 2% and 13% of the polychaetes
at four Pacific sites. Tselepides and Eleftheriou (1992)
reported that 49–52% of the polychaetes between 700
and 1000 m depth off Crete were carnivorous.
Fig. 2.16. Examples of deep-sea nematodes that are thought to be
carnivores because their buccal cavities have teeth as do carnivorous
nematodes in shallow water. Only the anterior portion of each worm
is shown. Modified from Jensen (1992). Reproduced by permission
of the Station Biologique de Roscoff.
In the food-poor deep sea, prey are rare, so the time
between encounters with prey will be long compared
to that needed to subdue and ingest a prey item
once encountered. Under these circumstances, optimalforaging theory predicts that diets should be generalized to shorten the time between prey encounters,
increasing the food-acquisition rate (MacArthur, 1972).
The step from feeding on live prey to including carrion
in the diet is a small one, so organisms that might be
predators in shallow water are likely to consume both