FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
333
where microbial activity is most intense (Deming
and Colwell, 1985; Wirsen and Jannasch, 1986).
Furthermore, large differences in microbial activity
at this interface are found between oligotrophic and
eutrophic sites in the abyss (Sibuet et al., 1993).
These results contrast sharply with the results from the
Alvin sandwiches, referred to earlier, which indicated
inhibition of microbial activity at great depths unless
accompanied by metazoan activity. Some explanation
has come from data showing activity of pressureadapted (barophilic) heterotrophic bacteria in or at
the deep seabed is different from that associated with
particles sinking down from the surface, whose activity
and biomass become minimal below about 2000 m
(Suess, 1988). Moreover, the activity of barophiles of
the deep-sea bed adapted to low temperatures seems to
vary in response to the quality, as well as quantity, of
detrital material available (Patching and Eardly, 1997).
Response by meiofauna and Foraminifera
Little is known of the feeding characteriztics of
metazoans belonging to the meiofauna. Yet this size
class, consisting of both metazoans as well as larger
protozoans, includes the most numerous members of
the benthic fauna, and plays an important role in
energy flow in the benthic system (Gooday et al.,
1992; Tietjen, 1992). Meiofauna such as nematodes
are thought to be important microbial grazers, probably
themselves forming an important food source for
deposit feeders. That these organisms do not depend
directly on fresh particulate organic matter, but rather
on grazing smaller organisms is supported by stable
isotope studies (Iken et al., 2001). Stable isotope
studies on komokiaceans (non-shelled foraminiferans
with soft tests) also show strongly depleted values of
d
13 N compared to particulate organic matter, indicating
their main food also is not organic matter derived from
phytoplankton. However, Iken et al. found some species
with agglutinated tests and those forming ‘mudballs’
seem to depend more on phytoplankton-derived organic
matter, while miliolids are known to ingest fresh
phytodetritus (Gooday, 1988).
Sediment-community responses measured in
terms of bulk biochemical parameters
French work in the 1980s in the BIOGAS program
attempted to relate the organic composition of particle
flux, measured in sediment traps at different stations
in the Bay of Biscay (Northeast Atlantic), to that
measured in the sediment (Khripounoff et al., 1985).
The measurements showed an order-of-magnitude drop
in the organic concentration in the superficial sediment
compared to that trapped, but lacked seasonal coverage.
The biochemical composition of this material was
dominated by refractory humic-type compounds of
high molecular weight which result from bacterial
transformations, followed by labile proteins (17.4%),
lipids (14%), refractory proteins (9.2%), and lastly
labile sugars (3%). An index of selective nutritional
utilization was derived as a coefficient of utilization
based on the concentration in the trapped particles in
relation to that in the sediment. This indicates that the
sediment community utilize first the lipids, then the
easily dissolved proteins and amino acids. The study
concluded that refractory material accounted for about
half of organic-matter mineralization in the energetics
of the abyssal ecosystem, but did not take into account
seasonality in particle flux or in the reactivity of the
system.
Seasonal coverage was part of another approach
by German workers employing bulk biochemical
measurements as indicators of sediment community
activity. Measurements of total adenylates [adenosine
triphosphate (ATP), adenosine diphosphate (ADP)
and adenosine monophosphate (AMP), reflecting the
amount of plasma within cells] and phospholipid
(reflecting the amount of biologically active surface
membranes) provide proxies for the total biomass
of benthic organisms in the small size class (bacteria, fungi, flagellate protozoans and small metazoan
meiofauna). As indicators of activity, particulate ATP
(found in mitochondria) and electron-transport-system
activity (ETSA), and later in the study potential
activity of hydrolytic enzymes, were measured. Results
using these parameters in a long-term program at the
German BIOTRANS site at 47ºN, 20ºW in the abyssal
Northeast Atlantic, where organic flux is measured as
total chloroplastic pigment equivalents (CPE) in the
sediment, has shown a sensitive response to changes
in organic flux (Pfannkuche, 1992, 1993).
Role of benthopelagic bacteria and
metazoan plankton in carbon utilization
and remineralization in the benthic boundary
layer
There have been few attempts to address the organic
utilization and metabolism of the bacterioplankton
(bacteria not attached to detrital particles) and zooplankton of the benthic boundary layer. This is despite
indications that the benthic bounday layer has the
potential to respond rapidly to food pulses, and shows
a high ingestion rate by zooplankton, suggesting that
333
where microbial activity is most intense (Deming
and Colwell, 1985; Wirsen and Jannasch, 1986).
Furthermore, large differences in microbial activity
at this interface are found between oligotrophic and
eutrophic sites in the abyss (Sibuet et al., 1993).
These results contrast sharply with the results from the
Alvin sandwiches, referred to earlier, which indicated
inhibition of microbial activity at great depths unless
accompanied by metazoan activity. Some explanation
has come from data showing activity of pressureadapted (barophilic) heterotrophic bacteria in or at
the deep seabed is different from that associated with
particles sinking down from the surface, whose activity
and biomass become minimal below about 2000 m
(Suess, 1988). Moreover, the activity of barophiles of
the deep-sea bed adapted to low temperatures seems to
vary in response to the quality, as well as quantity, of
detrital material available (Patching and Eardly, 1997).
Response by meiofauna and Foraminifera
Little is known of the feeding characteriztics of
metazoans belonging to the meiofauna. Yet this size
class, consisting of both metazoans as well as larger
protozoans, includes the most numerous members of
the benthic fauna, and plays an important role in
energy flow in the benthic system (Gooday et al.,
1992; Tietjen, 1992). Meiofauna such as nematodes
are thought to be important microbial grazers, probably
themselves forming an important food source for
deposit feeders. That these organisms do not depend
directly on fresh particulate organic matter, but rather
on grazing smaller organisms is supported by stable
isotope studies (Iken et al., 2001). Stable isotope
studies on komokiaceans (non-shelled foraminiferans
with soft tests) also show strongly depleted values of
d
13 N compared to particulate organic matter, indicating
their main food also is not organic matter derived from
phytoplankton. However, Iken et al. found some species
with agglutinated tests and those forming ‘mudballs’
seem to depend more on phytoplankton-derived organic
matter, while miliolids are known to ingest fresh
phytodetritus (Gooday, 1988).
Sediment-community responses measured in
terms of bulk biochemical parameters
French work in the 1980s in the BIOGAS program
attempted to relate the organic composition of particle
flux, measured in sediment traps at different stations
in the Bay of Biscay (Northeast Atlantic), to that
measured in the sediment (Khripounoff et al., 1985).
The measurements showed an order-of-magnitude drop
in the organic concentration in the superficial sediment
compared to that trapped, but lacked seasonal coverage.
The biochemical composition of this material was
dominated by refractory humic-type compounds of
high molecular weight which result from bacterial
transformations, followed by labile proteins (17.4%),
lipids (14%), refractory proteins (9.2%), and lastly
labile sugars (3%). An index of selective nutritional
utilization was derived as a coefficient of utilization
based on the concentration in the trapped particles in
relation to that in the sediment. This indicates that the
sediment community utilize first the lipids, then the
easily dissolved proteins and amino acids. The study
concluded that refractory material accounted for about
half of organic-matter mineralization in the energetics
of the abyssal ecosystem, but did not take into account
seasonality in particle flux or in the reactivity of the
system.
Seasonal coverage was part of another approach
by German workers employing bulk biochemical
measurements as indicators of sediment community
activity. Measurements of total adenylates [adenosine
triphosphate (ATP), adenosine diphosphate (ADP)
and adenosine monophosphate (AMP), reflecting the
amount of plasma within cells] and phospholipid
(reflecting the amount of biologically active surface
membranes) provide proxies for the total biomass
of benthic organisms in the small size class (bacteria, fungi, flagellate protozoans and small metazoan
meiofauna). As indicators of activity, particulate ATP
(found in mitochondria) and electron-transport-system
activity (ETSA), and later in the study potential
activity of hydrolytic enzymes, were measured. Results
using these parameters in a long-term program at the
German BIOTRANS site at 47ºN, 20ºW in the abyssal
Northeast Atlantic, where organic flux is measured as
total chloroplastic pigment equivalents (CPE) in the
sediment, has shown a sensitive response to changes
in organic flux (Pfannkuche, 1992, 1993).
Role of benthopelagic bacteria and
metazoan plankton in carbon utilization
and remineralization in the benthic boundary
layer
There have been few attempts to address the organic
utilization and metabolism of the bacterioplankton
(bacteria not attached to detrital particles) and zooplankton of the benthic boundary layer. This is despite
indications that the benthic bounday layer has the
potential to respond rapidly to food pulses, and shows
a high ingestion rate by zooplankton, suggesting that