338
John D. GAGE
Response and interactions at population level to
mass deposition
Scaling considerations again determine that only the
smallest size classes of organisms can show a response
in terms of enhanced population abundance. These may
themselves develop a mini food chain. For example,
samples of phytodetritus recovered from the surface of
multicores from the abyssal Northeast Atlantic became
colonized by a variety of prokaryote micro-organisms
(Lochte and Turley, 1988; Turley and Lochte, 1990b).
These in turn are consumed by benthic allogromiid,
textulariid and rotaliinid foraminifers, and by nematodes, which themselves also rapidly proliferated in
the phytodetritus (Gooday, 1988; Turley et al., 1988;
Gooday and Lambshead, 1989). A similar sequence of
events occurs following the fall-out of organic material
from surface production in shallow water (Graf et al.,
1983). The organic particles are colonized by zooflagellates, amoebae, ciliates, and small metazoans such as
rotifers and nematodes, which feed on the proliferating
bacterial and fungal microflora associated with the
particles of organic debris (see Fenchel, 1978).
In the deep Northeast Atlantic at 49ºN, Gooday
(1993) has described the foraminiferal colonizers of
phytodetritus as dominated by three species: two
rotaliids, Alabaminella weddellensis and Epistominella
exigua, and the allogromiid Tinogullmia riemanni.
Their populations are able to respond rapidly to
availability of phytodetrital floc, but numbers decline
in a spectacular fashion at the end of summer when
the material is no longer available (Gooday and Turley,
1990). These species are much rarer further south at
31ºN where only traces of phytodetritus have been
observed (Gooday, 1993). It has been demonstrated
experimentally that foraminifer species recovered from
abyssal cores, including Epistominella exigua, can
ingest microalgae supplied as food in high-pressure
and low-temperature incubations (Turley et al., 1993).
Because these species are not abundant in the sediment,
they may be specialized opportunists. Other deep-sea
foraminifers, like shallow-water forms, probably feed
either by uptake of dissolved organic matter, carnivory,
omnivory or suspension feeding (Lipps, 1983; Gooday
et al., 1992), while others feed on organic detritus
associated with sediment (Goldstein and Corliss, 1994).
These in turn are grazed by macrofaunal asellote
isopods, scaphopod molluscs and holothurians (Langer
et al., 1995; Billett et al., 1988; Svavarsson et al.,
1993).
Response of organisms within the sediment
The responses summarized above occur only within
the phytodetrital microenvironment and therefore represent responses by highly adapted species to an
‘opportunistic’ lifestyle. This may also be true to a certain extent with the more generalized deposit-feeding
elements of the sediment fauna below, which benefit
directly by grazing phytodetritus and its associated
micro-community. Other animals may benefit more
indirectly as a result of the organic enrichment from
faeces or dissolved metabolites from other consumers.
For example, although meiofaunal abundance is
proportional to organic-food availability (e.g., Vanreusel et al., 1995), metazoan meiofauna such as
nematodes may react in a less spectacular fashion
than foraminiferans to phytodetritus. However, a clear
increase in mean size of nematodes was shown at the
German BIOTRANS site from April to July, followed
by a sharp decrease (Soltwedel et al., 1996). Nematodes
are found deeper in sediment experiencing phytodetrital
mass accumulation than where such input is much
less, but this may merely result from the activity of
larger macrofaunal organisms mixing labile material
deep into the sediment (Lambshead et al., 1995).
However, this response is not shown by the metazoan
meiofauna as a whole. Cores sectioned from the North
Atlantic before and after a phytodetrital pulse showed
no general migration towards the sediment surface, or
any significant increase in population abundance. This
suggests that meiofaunal metazoans as a whole failed
to exploit phytodetritus as rapidly as Foraminifera
(Gooday et al., 1996). It was argued that this reflected a
competitive superiority of Foraminifera over metazoan
meiofauna in exploiting a recent sedimentation event.
However, the twofold increases in bulk abundance of
meiofauna (mainly nematodes) shown in seasonally
contrasting samples from the bathyal Mediterranean
(de Bov´ ee et al., 1990) and the Northeast Atlantic
along the Hebridean margin (Mitchell et al., 1997)
indicate a response over a longer time scale. Similarly,
in the Pacific at Station ‘M’ off California, Drazen
et al. (1998) found agglutinating foraminiferans and
most small metazoan taxa showed seasonal increases
in density during the winter months after detrital aggregates had disappeared and about 8 months after the
peak in sediment community oxygen consumption and
particulate sinking flux. Other work has demonstrated a
summer-time increase in the heterogeneity of nematode
populations in response to springtime deposition of
John D. GAGE
Response and interactions at population level to
mass deposition
Scaling considerations again determine that only the
smallest size classes of organisms can show a response
in terms of enhanced population abundance. These may
themselves develop a mini food chain. For example,
samples of phytodetritus recovered from the surface of
multicores from the abyssal Northeast Atlantic became
colonized by a variety of prokaryote micro-organisms
(Lochte and Turley, 1988; Turley and Lochte, 1990b).
These in turn are consumed by benthic allogromiid,
textulariid and rotaliinid foraminifers, and by nematodes, which themselves also rapidly proliferated in
the phytodetritus (Gooday, 1988; Turley et al., 1988;
Gooday and Lambshead, 1989). A similar sequence of
events occurs following the fall-out of organic material
from surface production in shallow water (Graf et al.,
1983). The organic particles are colonized by zooflagellates, amoebae, ciliates, and small metazoans such as
rotifers and nematodes, which feed on the proliferating
bacterial and fungal microflora associated with the
particles of organic debris (see Fenchel, 1978).
In the deep Northeast Atlantic at 49ºN, Gooday
(1993) has described the foraminiferal colonizers of
phytodetritus as dominated by three species: two
rotaliids, Alabaminella weddellensis and Epistominella
exigua, and the allogromiid Tinogullmia riemanni.
Their populations are able to respond rapidly to
availability of phytodetrital floc, but numbers decline
in a spectacular fashion at the end of summer when
the material is no longer available (Gooday and Turley,
1990). These species are much rarer further south at
31ºN where only traces of phytodetritus have been
observed (Gooday, 1993). It has been demonstrated
experimentally that foraminifer species recovered from
abyssal cores, including Epistominella exigua, can
ingest microalgae supplied as food in high-pressure
and low-temperature incubations (Turley et al., 1993).
Because these species are not abundant in the sediment,
they may be specialized opportunists. Other deep-sea
foraminifers, like shallow-water forms, probably feed
either by uptake of dissolved organic matter, carnivory,
omnivory or suspension feeding (Lipps, 1983; Gooday
et al., 1992), while others feed on organic detritus
associated with sediment (Goldstein and Corliss, 1994).
These in turn are grazed by macrofaunal asellote
isopods, scaphopod molluscs and holothurians (Langer
et al., 1995; Billett et al., 1988; Svavarsson et al.,
1993).
Response of organisms within the sediment
The responses summarized above occur only within
the phytodetrital microenvironment and therefore represent responses by highly adapted species to an
‘opportunistic’ lifestyle. This may also be true to a certain extent with the more generalized deposit-feeding
elements of the sediment fauna below, which benefit
directly by grazing phytodetritus and its associated
micro-community. Other animals may benefit more
indirectly as a result of the organic enrichment from
faeces or dissolved metabolites from other consumers.
For example, although meiofaunal abundance is
proportional to organic-food availability (e.g., Vanreusel et al., 1995), metazoan meiofauna such as
nematodes may react in a less spectacular fashion
than foraminiferans to phytodetritus. However, a clear
increase in mean size of nematodes was shown at the
German BIOTRANS site from April to July, followed
by a sharp decrease (Soltwedel et al., 1996). Nematodes
are found deeper in sediment experiencing phytodetrital
mass accumulation than where such input is much
less, but this may merely result from the activity of
larger macrofaunal organisms mixing labile material
deep into the sediment (Lambshead et al., 1995).
However, this response is not shown by the metazoan
meiofauna as a whole. Cores sectioned from the North
Atlantic before and after a phytodetrital pulse showed
no general migration towards the sediment surface, or
any significant increase in population abundance. This
suggests that meiofaunal metazoans as a whole failed
to exploit phytodetritus as rapidly as Foraminifera
(Gooday et al., 1996). It was argued that this reflected a
competitive superiority of Foraminifera over metazoan
meiofauna in exploiting a recent sedimentation event.
However, the twofold increases in bulk abundance of
meiofauna (mainly nematodes) shown in seasonally
contrasting samples from the bathyal Mediterranean
(de Bov´ ee et al., 1990) and the Northeast Atlantic
along the Hebridean margin (Mitchell et al., 1997)
indicate a response over a longer time scale. Similarly,
in the Pacific at Station ‘M’ off California, Drazen
et al. (1998) found agglutinating foraminiferans and
most small metazoan taxa showed seasonal increases
in density during the winter months after detrital aggregates had disappeared and about 8 months after the
peak in sediment community oxygen consumption and
particulate sinking flux. Other work has demonstrated a
summer-time increase in the heterogeneity of nematode
populations in response to springtime deposition of