FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
317
various invertebrates of benthopelagic habit (usually
swimming or drifting in the water immediately overlying the ocean floor, but sometimes able to spend varying amounts of time on, or buried within, the seabed),
particularly penaeid prawns, periodically ascend to
feed on pelagic animals. Benthopelagic fish, however,
are thought to be major consumers of diel migrating
mesopelagic biomass (from depths of 200 to 1000 m),
either captured near the bottom (e.g., Sedberry and
Musick, 1978), or through vertical migration by the fish
predator. For example, some benthopelagic fish, such
as hake, prey on mesopelagic organisms, including
smaller fish that perform diel migrations (Blaber and
Bulman, 1987). On the continental margin many deepwater benthopelagic fish are thought to feed almost
exclusively on mesopelagic organisms whose distributions and migrations take place on the slope (Mauchline
and Gordon, 1991). Some fish, such as the orange
roughy, also play an important rˆ ole by staying at depth,
aggregated around sea mounts and submerged banks,
and feeding on enhanced flux of prey drifting past
these features, as well as on diel migrators during their
downward migration (Koslow, 1997). By this means
they are important in the transfer of energy as organic
carbon to the deep-sea benthos (Rosecchi et al., 1988).
The deep-sea scavenging community will also fall into
the category of large benthopelagic predators, because
these animals, which range from actively swimming
fish to highly motile swimming invertebrates, tend
to remain within the benthic boundary layer. These
organisms (see below) will therefore serve only to
redistribute the already sparse concentrations of organic
material over the seabed.
Energetic considerations
Some idea of the energetic losses associated with the
links in the midwater food chain may be obtained from
measurements of the dramatic decline in macroplankton and micronekton biomass with depth. Although
there is an increase in mean body size of bathypelagic
organisms with increasing depth (Mauchline, 1972),
this is accompanied by an order-of-magnitude drop in
biomass from the surface to 2000 m and a further orderof-magnitude drop to a depth of 4000 m (Angel and
Baker, 1982).
SMALL PARTICLES
Small particles have long been thought to be the
chief means of organic-material input to the deep-sea
heterotrophic ecosystem. They are small because of
the size structure of the plankton community, with its
primary producers typically unicellular. The detrital
rain exported to the deep ocean actually consists of
a range of small particles. Passive aggregation to
form marine snow, or active aggregation as faecal
pellets or dead zooplankton, however, results in largersized particles with a faster sinking potential (McCave,
1975).
Because small-particle flux is the most important
source of organic carbon to the deep ocean, largescale patterns in the distribution of deep-sea benthic
biomass, both in terms of organism size and density
(Chapter 10), should relate to large-scale patterns
in primary productivity at the surface. The latter,
of course, should be indicative of the transfer to
the bottom of the new and recycled production (see
Chapter 3). Russian studies world-wide after World
War II have shown that this is broadly true at the
regional scale (see Belyaev, 1972). Although increasing
depth is associated with rapidly decreasing benthic
biomass as a consequence of midwater utilization,
benthic biomass, particularly near continental margins,
will also be much affected by laterally transported
particles resuspended from the bottom. I shall consider
this rapidly expanding area of study later in conjunction
with associated processs in the benthic boundary
layer.
Typically, the amount of small-particle material
caught in deep-ocean sediment traps is equivalent to
a mass flux of between 7 and 45 g m
−2 yr
−1 . If particles
sink at rates between 20 and ~1000 m day
−1 , these traps
need to be set well above the benthic boundary layer in
order to avoid collecting resuspended aggregates, the
so-called rebound flux of Gardner and Walsh (1990)
(see p. 329 on upwards flux of biogenic particles).
This mass flux will in turn be seen broadly reflected in
the pattern of organic-carbon content in the sediment,
or better, in measures such as chloroplastic pigment
equivalents (CPE) that directly reflect the amount of
organic material derived from primary production (e.g.,
Pfannkuche et al., 1983). For example, in the North
Atlantic north of 20ºN, the organic-carbon content of
the sediment increases with latitude and decreases with
depth out to the abyssal plains. From 20ºN to the
equator the pattern is more variable, being influenced
by coastal upwelling off Northwest Africa.
317
various invertebrates of benthopelagic habit (usually
swimming or drifting in the water immediately overlying the ocean floor, but sometimes able to spend varying amounts of time on, or buried within, the seabed),
particularly penaeid prawns, periodically ascend to
feed on pelagic animals. Benthopelagic fish, however,
are thought to be major consumers of diel migrating
mesopelagic biomass (from depths of 200 to 1000 m),
either captured near the bottom (e.g., Sedberry and
Musick, 1978), or through vertical migration by the fish
predator. For example, some benthopelagic fish, such
as hake, prey on mesopelagic organisms, including
smaller fish that perform diel migrations (Blaber and
Bulman, 1987). On the continental margin many deepwater benthopelagic fish are thought to feed almost
exclusively on mesopelagic organisms whose distributions and migrations take place on the slope (Mauchline
and Gordon, 1991). Some fish, such as the orange
roughy, also play an important rˆ ole by staying at depth,
aggregated around sea mounts and submerged banks,
and feeding on enhanced flux of prey drifting past
these features, as well as on diel migrators during their
downward migration (Koslow, 1997). By this means
they are important in the transfer of energy as organic
carbon to the deep-sea benthos (Rosecchi et al., 1988).
The deep-sea scavenging community will also fall into
the category of large benthopelagic predators, because
these animals, which range from actively swimming
fish to highly motile swimming invertebrates, tend
to remain within the benthic boundary layer. These
organisms (see below) will therefore serve only to
redistribute the already sparse concentrations of organic
material over the seabed.
Energetic considerations
Some idea of the energetic losses associated with the
links in the midwater food chain may be obtained from
measurements of the dramatic decline in macroplankton and micronekton biomass with depth. Although
there is an increase in mean body size of bathypelagic
organisms with increasing depth (Mauchline, 1972),
this is accompanied by an order-of-magnitude drop in
biomass from the surface to 2000 m and a further orderof-magnitude drop to a depth of 4000 m (Angel and
Baker, 1982).
SMALL PARTICLES
Small particles have long been thought to be the
chief means of organic-material input to the deep-sea
heterotrophic ecosystem. They are small because of
the size structure of the plankton community, with its
primary producers typically unicellular. The detrital
rain exported to the deep ocean actually consists of
a range of small particles. Passive aggregation to
form marine snow, or active aggregation as faecal
pellets or dead zooplankton, however, results in largersized particles with a faster sinking potential (McCave,
1975).
Because small-particle flux is the most important
source of organic carbon to the deep ocean, largescale patterns in the distribution of deep-sea benthic
biomass, both in terms of organism size and density
(Chapter 10), should relate to large-scale patterns
in primary productivity at the surface. The latter,
of course, should be indicative of the transfer to
the bottom of the new and recycled production (see
Chapter 3). Russian studies world-wide after World
War II have shown that this is broadly true at the
regional scale (see Belyaev, 1972). Although increasing
depth is associated with rapidly decreasing benthic
biomass as a consequence of midwater utilization,
benthic biomass, particularly near continental margins,
will also be much affected by laterally transported
particles resuspended from the bottom. I shall consider
this rapidly expanding area of study later in conjunction
with associated processs in the benthic boundary
layer.
Typically, the amount of small-particle material
caught in deep-ocean sediment traps is equivalent to
a mass flux of between 7 and 45 g m
−2 yr
−1 . If particles
sink at rates between 20 and ~1000 m day
−1 , these traps
need to be set well above the benthic boundary layer in
order to avoid collecting resuspended aggregates, the
so-called rebound flux of Gardner and Walsh (1990)
(see p. 329 on upwards flux of biogenic particles).
This mass flux will in turn be seen broadly reflected in
the pattern of organic-carbon content in the sediment,
or better, in measures such as chloroplastic pigment
equivalents (CPE) that directly reflect the amount of
organic material derived from primary production (e.g.,
Pfannkuche et al., 1983). For example, in the North
Atlantic north of 20ºN, the organic-carbon content of
the sediment increases with latitude and decreases with
depth out to the abyssal plains. From 20ºN to the
equator the pattern is more variable, being influenced
by coastal upwelling off Northwest Africa.