348
John D. GAGE
organic material as they traverse the bottom. Over
a 90-day period from March to June 1991 at the
Station ‘M’ at a depth of 4100 m off California,
these authors estimated that 8.7% of the available
particulate organic carbon would have been taken up
in the 20 m
2 area monitored photographically. In order
to translate this to an estimate of how much was
mineralized to carbon dioxide, K.L. Smith et al. used
data on population densities, size structure and oxygen
consumption for the two dominant species, the elasipod
holothurians Elpidia minutissima and Peniagone vitrea.
(Weight-specific oxygen consumption was estimated
from data from a similar species, Scotoplanes globosa.)
Total respiratory uptake was converted to carbon
equivalent assuming a respiratory quotient of 0.85.
The total value, 0.012 g C m
−2 , represented 18.3% of
the total particulate organic carbon ingested by these
deposit-feeding megafaunal species. This concurs with
the estimate of assimilation efficiency for depositfeeding holothurians of Khripounoff and Sibuet (1980).
This estimated mineralization represents only 1.6% of
total flux of particulate organic carbon concurrently
measured 50 metres above the bottom at Station ‘M’
over the three-month period. Although this low value
is in agreement with the 1% estimate of Lampitt
et al. (1986) for megafauna at 4000 m, they both
contrast with the higher value of 7–10% of total flux
of particulate organic carbon estimated by K.L. Smith
(1992) for the abyssal central North Pacific.
Lauerman et al. (1997) used their stable isotope data
showing rapid ingestion of settling particulate organic
carbon, in conjunction with densities of the epifaunal
holothurians Abyssocucumis abyssorum and Oneirophanta mutabilis (previously estimated by Lauerman
et al., 1996, from towed photosled surveys), to deduce
how much of the vertical flux was being processed by
motile deposit-feeding megafauna during the high-flux
period in summertime at Station ‘M’ off California.
Assuming a gut passage time of six days the amount
of sediment that could be ingested (m
−2 d
−1 ) could
be compared to mean downwards flux from sediment
traps. Lauerman et al. (1997) were able to calculate
that this population of Abyssocucumis abyssorum could
process 0.2 to 4% of the sedimented organic material
during the period of vertical flux, assuming that 91%
of gut mass consisted of freshly deposited material.
Miller et al. (2000) indicate that this estimate may be
unreasonably low because a gut throughput time of
24 hours rather than 6 days is more likely to apply
to A. abyssorum. This would increase the estimated
ingestion rate to between 1.2 and 24% of the total flux
of particulate organic carbon, a value more in line with
their estimate for another species (Pannychia moseleyi)
of comparable density.
In a study by Miller et al. (2000) in the Santa
Catalina Basin off California using
234 Th as a tracer,
the surface-deposit feeding megafauna are concluded,
astonishingly, to be processing on average 39 to 52% of
the daily flux to the sea floor of excess
234 Th activity.
Based on an assimilation efficiency of about 15%,
the authors suggest that this implies that Bathybembix
bairdii, Chirodota sp. and Pannychia moseleyi may be
respiring 4 to 11% of the vertical flux of particulate
organic carbon. This estimate is in agreement with
that of K.L. Smith (1992) for the megafaunal depositfeeding fraction of the benthic community in the central
North Pacific.
Miller et al. (2000) point out that, although megafaunal deposit feeders are efficient selectors of highgrade organic matter, their assimilation efficiencies for
particulate organic carbon (about 15%) mean that the
faeces is still relatively enriched compared to surface
sediment. This provides both opportunities for further
microbial decomposition and, particularly when buried
by subducting bioturbating organisms, geochemical
‘hot-spots’ within the sediment. This contributes not
only towards organic-matter preservation but also
probably to greater patchiness in food resources, which
may be important in promoting high local species
diversity in deep-sea sediments (Snelgrove et al., 1992;
Gage, 1996).
Respiratory demand by benthic metazoans
One expected consequence of the deep sea as a
‘low-activity’ ecosystem would be low rates of individual metabolism among metazoans. Estimating
respiration of individual invertebrate animals from
the deep sea is very difficult. Low rates of oxygen
consumption measured from specimens recompressed
after collection from bathyal depths may be affected
by the drastic changes in pressure and temperature
experienced during capture. Childress et al. (1990)
could find no significant relationship between oxygen
consumption and depth when the data were adjusted
to take into account moderate metabolic dependency
on temperature. Furthermore, in situ measurements
on specimens lured into enclosures need to take into
account unknown behavioural effects on respiration
caused by the unnatural conditions.
John D. GAGE
organic material as they traverse the bottom. Over
a 90-day period from March to June 1991 at the
Station ‘M’ at a depth of 4100 m off California,
these authors estimated that 8.7% of the available
particulate organic carbon would have been taken up
in the 20 m
2 area monitored photographically. In order
to translate this to an estimate of how much was
mineralized to carbon dioxide, K.L. Smith et al. used
data on population densities, size structure and oxygen
consumption for the two dominant species, the elasipod
holothurians Elpidia minutissima and Peniagone vitrea.
(Weight-specific oxygen consumption was estimated
from data from a similar species, Scotoplanes globosa.)
Total respiratory uptake was converted to carbon
equivalent assuming a respiratory quotient of 0.85.
The total value, 0.012 g C m
−2 , represented 18.3% of
the total particulate organic carbon ingested by these
deposit-feeding megafaunal species. This concurs with
the estimate of assimilation efficiency for depositfeeding holothurians of Khripounoff and Sibuet (1980).
This estimated mineralization represents only 1.6% of
total flux of particulate organic carbon concurrently
measured 50 metres above the bottom at Station ‘M’
over the three-month period. Although this low value
is in agreement with the 1% estimate of Lampitt
et al. (1986) for megafauna at 4000 m, they both
contrast with the higher value of 7–10% of total flux
of particulate organic carbon estimated by K.L. Smith
(1992) for the abyssal central North Pacific.
Lauerman et al. (1997) used their stable isotope data
showing rapid ingestion of settling particulate organic
carbon, in conjunction with densities of the epifaunal
holothurians Abyssocucumis abyssorum and Oneirophanta mutabilis (previously estimated by Lauerman
et al., 1996, from towed photosled surveys), to deduce
how much of the vertical flux was being processed by
motile deposit-feeding megafauna during the high-flux
period in summertime at Station ‘M’ off California.
Assuming a gut passage time of six days the amount
of sediment that could be ingested (m
−2 d
−1 ) could
be compared to mean downwards flux from sediment
traps. Lauerman et al. (1997) were able to calculate
that this population of Abyssocucumis abyssorum could
process 0.2 to 4% of the sedimented organic material
during the period of vertical flux, assuming that 91%
of gut mass consisted of freshly deposited material.
Miller et al. (2000) indicate that this estimate may be
unreasonably low because a gut throughput time of
24 hours rather than 6 days is more likely to apply
to A. abyssorum. This would increase the estimated
ingestion rate to between 1.2 and 24% of the total flux
of particulate organic carbon, a value more in line with
their estimate for another species (Pannychia moseleyi)
of comparable density.
In a study by Miller et al. (2000) in the Santa
Catalina Basin off California using
234 Th as a tracer,
the surface-deposit feeding megafauna are concluded,
astonishingly, to be processing on average 39 to 52% of
the daily flux to the sea floor of excess
234 Th activity.
Based on an assimilation efficiency of about 15%,
the authors suggest that this implies that Bathybembix
bairdii, Chirodota sp. and Pannychia moseleyi may be
respiring 4 to 11% of the vertical flux of particulate
organic carbon. This estimate is in agreement with
that of K.L. Smith (1992) for the megafaunal depositfeeding fraction of the benthic community in the central
North Pacific.
Miller et al. (2000) point out that, although megafaunal deposit feeders are efficient selectors of highgrade organic matter, their assimilation efficiencies for
particulate organic carbon (about 15%) mean that the
faeces is still relatively enriched compared to surface
sediment. This provides both opportunities for further
microbial decomposition and, particularly when buried
by subducting bioturbating organisms, geochemical
‘hot-spots’ within the sediment. This contributes not
only towards organic-matter preservation but also
probably to greater patchiness in food resources, which
may be important in promoting high local species
diversity in deep-sea sediments (Snelgrove et al., 1992;
Gage, 1996).
Respiratory demand by benthic metazoans
One expected consequence of the deep sea as a
‘low-activity’ ecosystem would be low rates of individual metabolism among metazoans. Estimating
respiration of individual invertebrate animals from
the deep sea is very difficult. Low rates of oxygen
consumption measured from specimens recompressed
after collection from bathyal depths may be affected
by the drastic changes in pressure and temperature
experienced during capture. Childress et al. (1990)
could find no significant relationship between oxygen
consumption and depth when the data were adjusted
to take into account moderate metabolic dependency
on temperature. Furthermore, in situ measurements
on specimens lured into enclosures need to take into
account unknown behavioural effects on respiration
caused by the unnatural conditions.