FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
319
remains difficult to quantify. These events will range
from events that are quickly utilized by the benthic
community to those resulting in long-lived mass
accumulations of detrital material on the deep ocean
bed, and even depositions which, from deep sedimentcore evidence, may completely overwhelm and smother
the benthic community (Kemp and Baldauf, 1993).
Particle aggregation and ‘marine snow’
Fine particles of sinking organic material are subject to
aggregation, thus increasing their size to the range of
millimetres, and consequently their rate of sinking. This
discovery in the late 1970s displaced the widely held
view that the deep-sea ecosystem is the recipient of a
continuous, sparse rain of very fine particles taking perhaps months or years to sink down. These aggregated,
intermediate particles make up the chief constituents of
the material caught in deep oceanic-sediment traps. But
they are extremely difficult to collect intact, and their
amorphous and highly variable shape, from which their
name ‘marine snow’ was coined by Japanese workers,
are best seen by scuba divers, or from the viewing port
of a manned submersible. Because of their size, the
sinking rates of this particulate matter are commonly
between 100 and 1000 m day
−1 (McCave, 1975). The
aggregation into many larger particles was originally
thought to be exclusively driven by biological processes
or packaging, where feeding by heterotrophs will
eventually repackage particles into larger faecal pellets
and other egesta (Fowler and Knauer, 1986). Other
processes are now recognized as important in aggregating small particles. These include physical processes,
such as Brownian movement, which dominate in the
interactions between the smallest particles. Differential
settling and water turbulence will promote collisions
between particles, which bind together and capture
further smaller particles into macroscopic aggregates
(McCave, 1984; Angel, 1984; Fowler and Knauer,
1986; Alldredge and Silver, 1988; Jackson, 1990;
Alldredge and McGillivary, 1991). Lampitt (1996)
has provided a readable, and less technical account
of marine snow. Marine-snow particles are generally
larger than about 100 mm, and up to many centimetres
across. They sink down at rates measured between
1 and 368 m day
−1 (Diercks and Asper, 1997), in
agreement with estimates of the time interval between
phytoplankton blooms and interception in traps or
accumulation on the ocean floor. The agents binding
marine snow are sticky mucus exudates composed
of polysaccharides secreted by phytoplankton and
bacteria. Because these particles may collide and stick
to much smaller, more numerous particles with a lower
sinking rate, they will act slowly to clear nepheloid
layers of fine particles (Hill and Nowell, 1990). As the
flocculent particles sink down they also scavenge other
particles, such as algal cells and small faecal pellets,
thus accelerating their sinking (Kranck and Milligan,
1988). This process is thought to be important in the
growth of the larger snow particles (Alldredge and
Gotschalk, 1989).
It is probable also that such aggregates are constantly
being disaggregated or eaten. Each aggregate may
form a microhabitat rich in microbial communities
and nutrients. Within each aggregate, processes of
decomposition and nutrient regeneration will occur
at greater intensity than in the surrounding water,
so that their chemical and biological characteriztics
change rapidly. Sinking rate is enhanced by their
increased size and mass, but this flocculent material
typically is composed of detritus, carrying large
numbers of tiny attached phototrophic and microheterotrophic organisms including bacteria, and some
inorganic matter – mostly clay particles. In some
areas marine snow includes the bodies of gelatinous
pelagic macrozooplankton, particularly salps and the
abandoned gelatinous ‘houses’ of larvaceans whose
mucous composition particularly improves particle
adhesion (Angel, 1984; Smetacek, 1985; Alldredge
and Silver, 1988; Alldredge and Gotschalk, 1989;
Lampitt et al., 1993; Pfannkuche and Lochte, 1993).
Salps, because of their high rate of growth, may
create dense swarms at the ocean surface at middle
latitudes (Wiebe et al., 1979; Iseki, 1981; Matsueda
et al., 1986; Bathmann, 1988; Morris et al., 1988).
Off California, larvacaean ‘houses’ alone have been
estimated seasonally to provide a huge proportion
of the larger-sized particles below the euphotic zone
(Silver et al., 1998).
‘Marine snow’ as habitat for microbial activity
Marine-snow particles might be thought to be
an important site for microbial degradation and a
habitat for microzooplankton. Paradoxically, Fowler
and Knauer (1986) and Karl et al. (1988) found they are
rather poor habitats for microbial growth at depth. This
is probably because surface-living bacteria are carried
down with these particles into deeper water (Lochte and
Turley, 1988). Pressure-related effects much diminish
their role in organic degradation, so that below depths
319
remains difficult to quantify. These events will range
from events that are quickly utilized by the benthic
community to those resulting in long-lived mass
accumulations of detrital material on the deep ocean
bed, and even depositions which, from deep sedimentcore evidence, may completely overwhelm and smother
the benthic community (Kemp and Baldauf, 1993).
Particle aggregation and ‘marine snow’
Fine particles of sinking organic material are subject to
aggregation, thus increasing their size to the range of
millimetres, and consequently their rate of sinking. This
discovery in the late 1970s displaced the widely held
view that the deep-sea ecosystem is the recipient of a
continuous, sparse rain of very fine particles taking perhaps months or years to sink down. These aggregated,
intermediate particles make up the chief constituents of
the material caught in deep oceanic-sediment traps. But
they are extremely difficult to collect intact, and their
amorphous and highly variable shape, from which their
name ‘marine snow’ was coined by Japanese workers,
are best seen by scuba divers, or from the viewing port
of a manned submersible. Because of their size, the
sinking rates of this particulate matter are commonly
between 100 and 1000 m day
−1 (McCave, 1975). The
aggregation into many larger particles was originally
thought to be exclusively driven by biological processes
or packaging, where feeding by heterotrophs will
eventually repackage particles into larger faecal pellets
and other egesta (Fowler and Knauer, 1986). Other
processes are now recognized as important in aggregating small particles. These include physical processes,
such as Brownian movement, which dominate in the
interactions between the smallest particles. Differential
settling and water turbulence will promote collisions
between particles, which bind together and capture
further smaller particles into macroscopic aggregates
(McCave, 1984; Angel, 1984; Fowler and Knauer,
1986; Alldredge and Silver, 1988; Jackson, 1990;
Alldredge and McGillivary, 1991). Lampitt (1996)
has provided a readable, and less technical account
of marine snow. Marine-snow particles are generally
larger than about 100 mm, and up to many centimetres
across. They sink down at rates measured between
1 and 368 m day
−1 (Diercks and Asper, 1997), in
agreement with estimates of the time interval between
phytoplankton blooms and interception in traps or
accumulation on the ocean floor. The agents binding
marine snow are sticky mucus exudates composed
of polysaccharides secreted by phytoplankton and
bacteria. Because these particles may collide and stick
to much smaller, more numerous particles with a lower
sinking rate, they will act slowly to clear nepheloid
layers of fine particles (Hill and Nowell, 1990). As the
flocculent particles sink down they also scavenge other
particles, such as algal cells and small faecal pellets,
thus accelerating their sinking (Kranck and Milligan,
1988). This process is thought to be important in the
growth of the larger snow particles (Alldredge and
Gotschalk, 1989).
It is probable also that such aggregates are constantly
being disaggregated or eaten. Each aggregate may
form a microhabitat rich in microbial communities
and nutrients. Within each aggregate, processes of
decomposition and nutrient regeneration will occur
at greater intensity than in the surrounding water,
so that their chemical and biological characteriztics
change rapidly. Sinking rate is enhanced by their
increased size and mass, but this flocculent material
typically is composed of detritus, carrying large
numbers of tiny attached phototrophic and microheterotrophic organisms including bacteria, and some
inorganic matter – mostly clay particles. In some
areas marine snow includes the bodies of gelatinous
pelagic macrozooplankton, particularly salps and the
abandoned gelatinous ‘houses’ of larvaceans whose
mucous composition particularly improves particle
adhesion (Angel, 1984; Smetacek, 1985; Alldredge
and Silver, 1988; Alldredge and Gotschalk, 1989;
Lampitt et al., 1993; Pfannkuche and Lochte, 1993).
Salps, because of their high rate of growth, may
create dense swarms at the ocean surface at middle
latitudes (Wiebe et al., 1979; Iseki, 1981; Matsueda
et al., 1986; Bathmann, 1988; Morris et al., 1988).
Off California, larvacaean ‘houses’ alone have been
estimated seasonally to provide a huge proportion
of the larger-sized particles below the euphotic zone
(Silver et al., 1998).
‘Marine snow’ as habitat for microbial activity
Marine-snow particles might be thought to be
an important site for microbial degradation and a
habitat for microzooplankton. Paradoxically, Fowler
and Knauer (1986) and Karl et al. (1988) found they are
rather poor habitats for microbial growth at depth. This
is probably because surface-living bacteria are carried
down with these particles into deeper water (Lochte and
Turley, 1988). Pressure-related effects much diminish
their role in organic degradation, so that below depths