FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
347
mixing model of C.R. Smith et al. (1993). A burrowing, surface-deposit feeding chirodotid holothurian,
Chirodota sp., and a surface-deposit feeding trochid
gastropod, Bathybembix bairdii, were less enriched in
gut
234 Th, perhaps reflecting less selectivity, or reduced
opportunity for selectivity through lower motility.
In contrast, similar measurements on the Hawaiian
slope from gut contents of two synallactid holothurian
surface-deposit feeders, Mesothuria carnosa and Paleopatides retifer, were not enriched in
234 Th, but were
enriched in chlorophyll-a. This, however, may show
that in some situations involving frequent sediment
resuspension the excess
234 Th activity is a poor tracer
for fresh food-rich particles.
In a study of the benthic food web at the BENGAL
study site in the Northeast Atlantic, stable isotope
analysis has been used to investigate the trophic relationships in the total benthic fauna (Iken et al., 2001).
Naturally occurring stable isotopes of both carbon and
nitrogen show a stepwise enrichment between prey and
consumer tissue, with
13 N/
15 N activity ratios providing
a more conservative estimate of enrichment among
various biochemical fractions, and therefore a more
reliable tracer, than d
13 C (the d notation referring to the
12 C/
13 C activity expressed against a standard). Analysis
by these authors of d
13 N values and gut contents of
the epibenthic, deposit-feeding holothurians Amperima
rosea, Ellipinion sp. and Peniagone diaphana showed
that these animals feed mainly on freshly deposited
phytodetritus. Both A. rosea and P. diaphana have
gelatinous, buoyant bodies and are thought to be highly
motile, and furthermore seemed to have considerable
quantities of phytodetritus in their gut at all times
of the year, indicating very efficient foraging (Iken
et al., 2001). Values for d
13 N measured in another,
larger and less motile group of holothurians (including
the species Deima validum, Oneirophanta mutabilis
and Psychropotes longicauda) were higher, and this is
interpreted by Iken et al. as reflecting a diet including
older and more recycled organic matter than that
taken by the smaller, more buoyant species above.
A third group of holothurians including less motile
forms such as Pseudostichopus villosus (a sausageshaped epibenthic species which ploughs through the
superficial sediment) and Molpadia blakei (a burrowing
deposit feeder) have the highest values of d
13 N. It is
in these species, which may possess enteric bacteria
able to break down refractory organic material for
assimilation by the holothurian, that there may also be
enzymatic patterns in the gut enabling them to break
down bacterial membranes.
Particle selectivity can be inferred from analysis
of stomach contents of other megafauna collected at
different times of the year in the BENGAL program
during the late 1990s. Other work at the BENGAL
site on the Porcupine Abyssal Plain (Ginger et al.,
2001) suggests that Amperima rosea and Ellipinion sp.
have, in less than four months, completely turned
over and selectively removed phytosterols (free fatty
acids) by eating freshly arriving phytodetritus and
superficial sediment. That megafauna may be important
in modifying the lipid content of organic matter
has been shown elsewhere (Smallwood et al., 1999).
These authors, working on the highly productive
continental margin off Oman, provided molecular and
photographic evidence that spider crabs and brittle
stars play a significant role in depletion of particulate
organic carbon in the sediment, these animals having a
tissue lipid composition indicative of metabolic alteration of phytoplankton-derived organic material. Dense
populations of epifaunal spider crabs and brittle stars
photographed at the base of the oxygen minimum zone
suggest that such megafauna have been responsible
for these changes in the sediment. Other holothurian
species at the BENGAL station, however, forage
successfully on more refractory material, possibly
assisted by gut bacteria (see above).
Karrh and Miller (1994) have shown, for an obligate
surface-deposit feeding acorn worm in the intertidal
zone, that feeding rate, measured by the rate of
egestion, varies in response to food quality (measured
as chlorophyll-a and protein concentration) of the
sediment processed. Such behaviour may be predicted
to occur also in the deep sea. Time-lapse photography
has shown that motile deposit-feeding epifauna, such
as echinoids and holothurians, living on the abyssal
seabed in the eastern North Pacific are more active
when fresh detrital material is present on the bottom
than at other times (K.L. Smith et al., 1993).
Particle turnover by deposit feeders
Although large motile deposit-feeding megafauna
make an important contribution to physical mixing,
burial and repackaging of the sediment (Lauerman
et al., 1997; Miller et al. 2000), their role in organic
recycling of organic matter on the deep-sea bed is more
equivocal. K.L. Smith et al. (1993) estimated carbon
demand based on an assumption that motile deposit
feeders take up all recently sedimented particulate
347
mixing model of C.R. Smith et al. (1993). A burrowing, surface-deposit feeding chirodotid holothurian,
Chirodota sp., and a surface-deposit feeding trochid
gastropod, Bathybembix bairdii, were less enriched in
gut
234 Th, perhaps reflecting less selectivity, or reduced
opportunity for selectivity through lower motility.
In contrast, similar measurements on the Hawaiian
slope from gut contents of two synallactid holothurian
surface-deposit feeders, Mesothuria carnosa and Paleopatides retifer, were not enriched in
234 Th, but were
enriched in chlorophyll-a. This, however, may show
that in some situations involving frequent sediment
resuspension the excess
234 Th activity is a poor tracer
for fresh food-rich particles.
In a study of the benthic food web at the BENGAL
study site in the Northeast Atlantic, stable isotope
analysis has been used to investigate the trophic relationships in the total benthic fauna (Iken et al., 2001).
Naturally occurring stable isotopes of both carbon and
nitrogen show a stepwise enrichment between prey and
consumer tissue, with
13 N/
15 N activity ratios providing
a more conservative estimate of enrichment among
various biochemical fractions, and therefore a more
reliable tracer, than d
13 C (the d notation referring to the
12 C/
13 C activity expressed against a standard). Analysis
by these authors of d
13 N values and gut contents of
the epibenthic, deposit-feeding holothurians Amperima
rosea, Ellipinion sp. and Peniagone diaphana showed
that these animals feed mainly on freshly deposited
phytodetritus. Both A. rosea and P. diaphana have
gelatinous, buoyant bodies and are thought to be highly
motile, and furthermore seemed to have considerable
quantities of phytodetritus in their gut at all times
of the year, indicating very efficient foraging (Iken
et al., 2001). Values for d
13 N measured in another,
larger and less motile group of holothurians (including
the species Deima validum, Oneirophanta mutabilis
and Psychropotes longicauda) were higher, and this is
interpreted by Iken et al. as reflecting a diet including
older and more recycled organic matter than that
taken by the smaller, more buoyant species above.
A third group of holothurians including less motile
forms such as Pseudostichopus villosus (a sausageshaped epibenthic species which ploughs through the
superficial sediment) and Molpadia blakei (a burrowing
deposit feeder) have the highest values of d
13 N. It is
in these species, which may possess enteric bacteria
able to break down refractory organic material for
assimilation by the holothurian, that there may also be
enzymatic patterns in the gut enabling them to break
down bacterial membranes.
Particle selectivity can be inferred from analysis
of stomach contents of other megafauna collected at
different times of the year in the BENGAL program
during the late 1990s. Other work at the BENGAL
site on the Porcupine Abyssal Plain (Ginger et al.,
2001) suggests that Amperima rosea and Ellipinion sp.
have, in less than four months, completely turned
over and selectively removed phytosterols (free fatty
acids) by eating freshly arriving phytodetritus and
superficial sediment. That megafauna may be important
in modifying the lipid content of organic matter
has been shown elsewhere (Smallwood et al., 1999).
These authors, working on the highly productive
continental margin off Oman, provided molecular and
photographic evidence that spider crabs and brittle
stars play a significant role in depletion of particulate
organic carbon in the sediment, these animals having a
tissue lipid composition indicative of metabolic alteration of phytoplankton-derived organic material. Dense
populations of epifaunal spider crabs and brittle stars
photographed at the base of the oxygen minimum zone
suggest that such megafauna have been responsible
for these changes in the sediment. Other holothurian
species at the BENGAL station, however, forage
successfully on more refractory material, possibly
assisted by gut bacteria (see above).
Karrh and Miller (1994) have shown, for an obligate
surface-deposit feeding acorn worm in the intertidal
zone, that feeding rate, measured by the rate of
egestion, varies in response to food quality (measured
as chlorophyll-a and protein concentration) of the
sediment processed. Such behaviour may be predicted
to occur also in the deep sea. Time-lapse photography
has shown that motile deposit-feeding epifauna, such
as echinoids and holothurians, living on the abyssal
seabed in the eastern North Pacific are more active
when fresh detrital material is present on the bottom
than at other times (K.L. Smith et al., 1993).
Particle turnover by deposit feeders
Although large motile deposit-feeding megafauna
make an important contribution to physical mixing,
burial and repackaging of the sediment (Lauerman
et al., 1997; Miller et al. 2000), their role in organic
recycling of organic matter on the deep-sea bed is more
equivocal. K.L. Smith et al. (1993) estimated carbon
demand based on an assumption that motile deposit
feeders take up all recently sedimented particulate