316
John D. GAGE
category, the living or dead organic entities conveyed
passively from origins in the upper ocean to utilization
at the bottom, shows wide variability in size of particle
and nutritive value, as well as sources. They range from
the small organic detrital particles called “detrital rain”,
through terrigenous and coastal plant debris, to falls of
animal carcasses ranging in size from zooplankton to
whales. These inputs to the deep-sea bed will be dealt
with in order from small to large.
Small particles may consist of the remains of
planktonic animals, including faecal pellets and moults,
as well as phytoplankton. Apart from some small, light
particles that are completely broken down in midwater,
most sink within days or weeks; but the smallest, which
may consist of very old carbon and lithogenic particles
along with isolated bacteria (Bauer and Druffel, 1998)
may stay suspended almost indefinitely. The final
category, dissolved organic matter (DOM), is derived
from particulate organic matter, and is highest in the
sediment and overlying water in organically enriched
areas. Arguably, this may be an important food source
for certain metazoans, and certainly for heterotrophic
bacteria. However, although quantitatively very large,
most of the dissolved organic-carbon pool of the oceans
is very old and refractory (and therefore probably of
very limited value in fuelling the deep-sea ecosystem),
whereas labile material is quickly utilized and kept at
threshold values.
This chapter also addresses the utilization of these
varied inputs in relation to modes of feeding and
other responses of organisms of the deep-sea bed
to these organic inputs at the differing space–time
scales of these processes. These are considered in
turn in the context of each category of particle. Not
only feeding mechanisms are included, but also the
aerobic and anaerobic utilization of organic-particle
flux by the sediment community. By feeding on these
particles, and breaking them down to fuel their activity,
growth and reproduction, organisms of the deep-sea
bed remineralize organic carbon to carbon dioxide.
Quantitatively most of this recycling of carbon is
mediated by micro-organisms, so this chapter also
briefly reviews measurements of aerobic respiratory
demand by the total sediment community of the deepsea bed.
After summarizing these various inputs and modes
of utilization of organic carbon to the benthic boundary
layer community, I shall also briefly consider what is
known of anabolic metabolism in deep-sea animals
as a major energetic pathway. This includes both
somatic and reproductive production of individuals and
populations and should be considered as an integral
part of understanding of the dynamics of the bottom
community as driven by organic carbon. Such population processes are also important in understanding
sensitivities to environmental change, including that
caused by man’s increasing intervention in this remote
environment.
The chapter then examines the combined feeding
activities and trophic interrelationships of the deepsea bed community. It finishes by examining attempts
to model the deep-sea bed food web by means of
intensive comprehensive study of single, hopefully
representative, sites. By such means the eventual aim
is to project energy flow, using the proxy of carbon
dynamics, from the local scale to the scale of the
regional and global deep-sea ecosystem.
ACTIVE BIOLOGICAL TRANSPORT TO THE
DEEP-SEA BENTHIC BOUNDARY
The importance of midwater biota as an important
medium for the transfer of organic carbon to the
deep-sea bed grew from studies after World War II
on the vertical migrations of large zooplankton and
nekton between the surface and the deep ocean. This
work had been stimulated by military observations
of vertically moving deep scattering layers, during
development of acoustic devices for anti-submarine
warfare. The scientific studies suggested the presence
of continuous faunal linkages based on predator–prey
relationships within a chain of different midwater
organisms. This was first developed by Russian workers
in the 1950s as a ‘ladder of vertical migrations theory’
(see Vinogradov and Tseitlin, 1983). Vertical diel
migrations by surface and midwater plankton and
micronekton (organisms intermediate between feebly
swimming plankton and active swimmers such as fish,
otherwise known as nekton) may actively transport
material in their guts after feeding at night in the
surface layers and defaecating at depths as great as
1000 m during the day (Wiebe et al., 1979; Angel,
1989; Longhurst and Harrison, 1989). Lampitt et al.
(1990) estimate that less than 5% of mass particle flux
may be actively transported to depth in this way.
Trophic coupling of benthopelagic fauna with
midwater fauna
Vereshchaka (1995) showed on continental slopes that
John D. GAGE
category, the living or dead organic entities conveyed
passively from origins in the upper ocean to utilization
at the bottom, shows wide variability in size of particle
and nutritive value, as well as sources. They range from
the small organic detrital particles called “detrital rain”,
through terrigenous and coastal plant debris, to falls of
animal carcasses ranging in size from zooplankton to
whales. These inputs to the deep-sea bed will be dealt
with in order from small to large.
Small particles may consist of the remains of
planktonic animals, including faecal pellets and moults,
as well as phytoplankton. Apart from some small, light
particles that are completely broken down in midwater,
most sink within days or weeks; but the smallest, which
may consist of very old carbon and lithogenic particles
along with isolated bacteria (Bauer and Druffel, 1998)
may stay suspended almost indefinitely. The final
category, dissolved organic matter (DOM), is derived
from particulate organic matter, and is highest in the
sediment and overlying water in organically enriched
areas. Arguably, this may be an important food source
for certain metazoans, and certainly for heterotrophic
bacteria. However, although quantitatively very large,
most of the dissolved organic-carbon pool of the oceans
is very old and refractory (and therefore probably of
very limited value in fuelling the deep-sea ecosystem),
whereas labile material is quickly utilized and kept at
threshold values.
This chapter also addresses the utilization of these
varied inputs in relation to modes of feeding and
other responses of organisms of the deep-sea bed
to these organic inputs at the differing space–time
scales of these processes. These are considered in
turn in the context of each category of particle. Not
only feeding mechanisms are included, but also the
aerobic and anaerobic utilization of organic-particle
flux by the sediment community. By feeding on these
particles, and breaking them down to fuel their activity,
growth and reproduction, organisms of the deep-sea
bed remineralize organic carbon to carbon dioxide.
Quantitatively most of this recycling of carbon is
mediated by micro-organisms, so this chapter also
briefly reviews measurements of aerobic respiratory
demand by the total sediment community of the deepsea bed.
After summarizing these various inputs and modes
of utilization of organic carbon to the benthic boundary
layer community, I shall also briefly consider what is
known of anabolic metabolism in deep-sea animals
as a major energetic pathway. This includes both
somatic and reproductive production of individuals and
populations and should be considered as an integral
part of understanding of the dynamics of the bottom
community as driven by organic carbon. Such population processes are also important in understanding
sensitivities to environmental change, including that
caused by man’s increasing intervention in this remote
environment.
The chapter then examines the combined feeding
activities and trophic interrelationships of the deepsea bed community. It finishes by examining attempts
to model the deep-sea bed food web by means of
intensive comprehensive study of single, hopefully
representative, sites. By such means the eventual aim
is to project energy flow, using the proxy of carbon
dynamics, from the local scale to the scale of the
regional and global deep-sea ecosystem.
ACTIVE BIOLOGICAL TRANSPORT TO THE
DEEP-SEA BENTHIC BOUNDARY
The importance of midwater biota as an important
medium for the transfer of organic carbon to the
deep-sea bed grew from studies after World War II
on the vertical migrations of large zooplankton and
nekton between the surface and the deep ocean. This
work had been stimulated by military observations
of vertically moving deep scattering layers, during
development of acoustic devices for anti-submarine
warfare. The scientific studies suggested the presence
of continuous faunal linkages based on predator–prey
relationships within a chain of different midwater
organisms. This was first developed by Russian workers
in the 1950s as a ‘ladder of vertical migrations theory’
(see Vinogradov and Tseitlin, 1983). Vertical diel
migrations by surface and midwater plankton and
micronekton (organisms intermediate between feebly
swimming plankton and active swimmers such as fish,
otherwise known as nekton) may actively transport
material in their guts after feeding at night in the
surface layers and defaecating at depths as great as
1000 m during the day (Wiebe et al., 1979; Angel,
1989; Longhurst and Harrison, 1989). Lampitt et al.
(1990) estimate that less than 5% of mass particle flux
may be actively transported to depth in this way.
Trophic coupling of benthopelagic fauna with
midwater fauna
Vereshchaka (1995) showed on continental slopes that