FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
353
of a single species of small, elasipod holothurian,
Amperima rosea, seems to have increased from 2–
3 to 6000 individuals per hectare over a nine-year
period. Other fauna, including the brittle star Ophiocten
hastatum, and another holothurian Ellipinion sp., have
also shown large population increases, although as
yet it is not known whether the changes apply to a
wider area, or whether the changes reflect patterns in
migration of more motile species. Gut contents analysis
by Iken et al. (2001) indicate these species ingest
phytodetritus, and Billett et al. (2001) speculate that the
changes have been driven by interannual variability, and
a long-term, upward trend in organic-matter supply to
the seabed.
PASSIVE ORGANIC INPUTS TO THE DEEP-SEA
BENTHIC BOUNDARY – LARGE PACKAGES OF
PLANT ORIGIN
The significance to the benthic and benthopelagic fauna
of the food source provided by terrestrial and coastal
plant debris was commented on by Moseley (1880)
in the results of the Challenger expedition, and later
by Agassiz (1888) in the cruises of the Blake. This
material consists of various branches, leaves, nuts and
fruits. Sampling by the Danish Galathea expedition
in the 1950s provided the basis for a systematic
review of the occurrence, and possible utilization by
the deep-sea fauna, of such large, fast-sinking, plant
remains in the deep sea (Wolff, 1976, 1979, 1980).
Because large plants exist only on land and in shallow
water, these inputs might be thought to be important
only in the deep sea just beyond the continentalshelf edge. However, a great deal of this material
may float for a long time before sinking, so that a
significant proportion finds its way into the abyssal
realm. Various downslope hydrodynamic processes (see
below) also transport detrital particles, some of coastal
and terrestrial plant detritus, onto the continental rise.
A number of macrobenthic species have become
adapted to utilization of plant remains in the deep sea
(see Wolff, 1979 for a systematic review). The overall
significance, however, of such inputs to the nutritive
budget of the deep-sea ecosystem, and to carbon
mineralization on the deep-sea bed in global terms,
remains obscure. However, deep trenches located near
island arcs may act as sumps for coastal sediment
and particulate terrestrial detritus advected from nearby
land masses (Wolff, 1976; George and Higgins, 1979;
see also Chapter 6) and then support much higher
benthic biomass than occurs on the adjacent abyssal
plain (Belyaev, 1972; Rowe, 1983). In this respect the
deep trenches reflect the importance of such organic
inputs, because mid-water consumption of smallparticle flux from surface production through such
great depths might otherwise result in an extremely low
benthic standing crop.
Macroalgae and seagrass
Seagrasses and macroalgae of coastal origin are
often encountered in samples from the seabed, and
from sediment traps set in mid-water. Furthermore,
observations from manned submersibles and ROVs
(remote-operated vehicles) have provided many images
of such material lying on the deep-sea bed. Although
such material may play only a small role in the
overall flux of organic material to the deep-sea bed
(Schoener and Rowe, 1970), considerable quantities of
material, such as the seagrass Thalassia, are washed
into deeper water during tropical storms (Menzies
et al., 1967; Menzies and Rowe, 1969). Debris from
macroalgae may be important adjacent to the coasts
over a wide geographic area (e.g., Alongi, 1990). At
high latitudes its availability may help to modulate the
short energy pulse from planktonic production, so that
food may be available to foraging benthos throughout
the year (Reichardt, 1987), and its availability at middle
latitudes may actually be intensified during winter
(Harrold et al., 1998).
Debris from macroalgae and seagrasses becomes
concentrated at the head of submarine canyons off
southern California (Harrold et al., 1998), supporting
dense benthic populations (Vetter, 1994; Vetter and
Dayton, 1998).
Evidence for the importance of macroalgae and
seagrass debris to the benthic community comes from
two sources. First, there may be a large associated
standing crop of macrofauna (e.g., Vetter and Dayton,
1998). Second, there is evidence from gut contents
that large epifaunal deposit feeders consume such
remains, along with terrestrial plant detritus including
wood (Wolff, 1979, 1980; Pawson, 1982; Young et al.,
1993). Carbon isotope (
13 C) analyses of gut contents
indicate that seagrass which has been storm-washed
off the coast, or rafted out to sink in deep water,
may provide an important part of diet of megafaunal
sea cucumbers and sea urchins in the Caribbean
(Suchanek et al., 1985). Other observations in the
353
of a single species of small, elasipod holothurian,
Amperima rosea, seems to have increased from 2–
3 to 6000 individuals per hectare over a nine-year
period. Other fauna, including the brittle star Ophiocten
hastatum, and another holothurian Ellipinion sp., have
also shown large population increases, although as
yet it is not known whether the changes apply to a
wider area, or whether the changes reflect patterns in
migration of more motile species. Gut contents analysis
by Iken et al. (2001) indicate these species ingest
phytodetritus, and Billett et al. (2001) speculate that the
changes have been driven by interannual variability, and
a long-term, upward trend in organic-matter supply to
the seabed.
PASSIVE ORGANIC INPUTS TO THE DEEP-SEA
BENTHIC BOUNDARY – LARGE PACKAGES OF
PLANT ORIGIN
The significance to the benthic and benthopelagic fauna
of the food source provided by terrestrial and coastal
plant debris was commented on by Moseley (1880)
in the results of the Challenger expedition, and later
by Agassiz (1888) in the cruises of the Blake. This
material consists of various branches, leaves, nuts and
fruits. Sampling by the Danish Galathea expedition
in the 1950s provided the basis for a systematic
review of the occurrence, and possible utilization by
the deep-sea fauna, of such large, fast-sinking, plant
remains in the deep sea (Wolff, 1976, 1979, 1980).
Because large plants exist only on land and in shallow
water, these inputs might be thought to be important
only in the deep sea just beyond the continentalshelf edge. However, a great deal of this material
may float for a long time before sinking, so that a
significant proportion finds its way into the abyssal
realm. Various downslope hydrodynamic processes (see
below) also transport detrital particles, some of coastal
and terrestrial plant detritus, onto the continental rise.
A number of macrobenthic species have become
adapted to utilization of plant remains in the deep sea
(see Wolff, 1979 for a systematic review). The overall
significance, however, of such inputs to the nutritive
budget of the deep-sea ecosystem, and to carbon
mineralization on the deep-sea bed in global terms,
remains obscure. However, deep trenches located near
island arcs may act as sumps for coastal sediment
and particulate terrestrial detritus advected from nearby
land masses (Wolff, 1976; George and Higgins, 1979;
see also Chapter 6) and then support much higher
benthic biomass than occurs on the adjacent abyssal
plain (Belyaev, 1972; Rowe, 1983). In this respect the
deep trenches reflect the importance of such organic
inputs, because mid-water consumption of smallparticle flux from surface production through such
great depths might otherwise result in an extremely low
benthic standing crop.
Macroalgae and seagrass
Seagrasses and macroalgae of coastal origin are
often encountered in samples from the seabed, and
from sediment traps set in mid-water. Furthermore,
observations from manned submersibles and ROVs
(remote-operated vehicles) have provided many images
of such material lying on the deep-sea bed. Although
such material may play only a small role in the
overall flux of organic material to the deep-sea bed
(Schoener and Rowe, 1970), considerable quantities of
material, such as the seagrass Thalassia, are washed
into deeper water during tropical storms (Menzies
et al., 1967; Menzies and Rowe, 1969). Debris from
macroalgae may be important adjacent to the coasts
over a wide geographic area (e.g., Alongi, 1990). At
high latitudes its availability may help to modulate the
short energy pulse from planktonic production, so that
food may be available to foraging benthos throughout
the year (Reichardt, 1987), and its availability at middle
latitudes may actually be intensified during winter
(Harrold et al., 1998).
Debris from macroalgae and seagrasses becomes
concentrated at the head of submarine canyons off
southern California (Harrold et al., 1998), supporting
dense benthic populations (Vetter, 1994; Vetter and
Dayton, 1998).
Evidence for the importance of macroalgae and
seagrass debris to the benthic community comes from
two sources. First, there may be a large associated
standing crop of macrofauna (e.g., Vetter and Dayton,
1998). Second, there is evidence from gut contents
that large epifaunal deposit feeders consume such
remains, along with terrestrial plant detritus including
wood (Wolff, 1979, 1980; Pawson, 1982; Young et al.,
1993). Carbon isotope (
13 C) analyses of gut contents
indicate that seagrass which has been storm-washed
off the coast, or rafted out to sink in deep water,
may provide an important part of diet of megafaunal
sea cucumbers and sea urchins in the Caribbean
(Suchanek et al., 1985). Other observations in the