Chapter 11
FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
John D. GAGE
INTRODUCTION
The biota of the deep-sea bed and the immediately
overlying layer of water, the benthic boundary layer,
constitute an almost totally heterotrophic ecosystem (its
metabolism reliant on breakdown of complex organic
molecules). It is also an allochthonous system. Except
at hydrothermal vents, and in sediment subject to
methane seepage (see Chapter 4), this typically comes
from organic-material flux to the deep ocean basins
from contemporary primary photosynthetic production
in the euphotic zone (the thin surface layer of the
oceans where light penetrates). Nearer to the continental margin increasing amounts of this organic input may
be derived from neritic (coastal) and terrestrial organic
material, in both particulate and dissolved form.
I shall not further consider non-photosynthetic,
chemosynthetic, production at hydrothermal vents and
methane seeps. Although estimates of the contribution
of these sources to global organic production are still
uncertain, they are unlikely to be more than trivial
and will not be further considered in this chapter (see
Chapter 4 for an account of chemosynthetically fuelled
communities in the deep sea). It is noted that these
chemosynthetic inputs occur directly at the deep-ocean
bed, and thus are not subject to the intense biological
reprocessing and mineralization in the upper water
column.
While food characteriztics strongly influence the
species composition of the community present, the
quantity and quality of food input to the seabed
community is the single most important determinant of
the abundance of populations in space and time, and
may also influence species richness (see Chapter 10).
Furthermore, because of the huge area covered by the
deep ocean, the dynamics of organic food consumption
and the recycling of this carbon by the allochthonous
system on the deep-sea bed is thought to be of
considerable importance to understanding of the global
carbon cycle, whose inputs are now significantly
augmented from combustion of fossil fuel.
Historical aspects
After discovery during the 19th century of life on
the floor of the deep ocean world-wide, there was
active discussion on how these remote populations are
sustained. The reports from the exploring voyages of
British navy ships Lightning and Porcupine in the
Northeast Atlantic and Mediterranean in the 1860s
(e.g., Jeffreys, 1869) and the famous world-encircling
voyage of H.M.S. Challenger in 1872–1876 (Thomson,
1880; Murray, 1895) address the transfer of organic
material as food to the bottom in the form of dead
surface-dwelling animals. These, and later expeditions
by ships of other nations, recognized the passive
sinking of organic particles as the main category
of food to the deep-sea ecosystem. Some of the
observations made, such as the quantitative importance
and seasonal nature of fast-sinking gelatinous plankton
to the deep ocean floor (Moseley, 1880), presaged
findings one hundred years later.
After World War II in the 1950s and 1960s there was
an extensive, world-wide program of deep-sea sampling by Russian workers. This prompted discussion
of nutritional sources and categorization of feeding
types in deep-sea benthic organisms (Sokolova, 1959).
The availability of new methods for measuring organic
carbon in organisms, in sediments and in sea water
then led to the first attempts to make a budget for
the marine organic-carbon cycle (Riley, 1970). At the
same time, new studies on the deep-sea benthos by
American workers in the 1960s led to fresh discussion
of the sources of nutrition for the remote community
313
FOOD INPUTS, UTILIZATION, CARBON FLOW AND ENERGETICS
John D. GAGE
INTRODUCTION
The biota of the deep-sea bed and the immediately
overlying layer of water, the benthic boundary layer,
constitute an almost totally heterotrophic ecosystem (its
metabolism reliant on breakdown of complex organic
molecules). It is also an allochthonous system. Except
at hydrothermal vents, and in sediment subject to
methane seepage (see Chapter 4), this typically comes
from organic-material flux to the deep ocean basins
from contemporary primary photosynthetic production
in the euphotic zone (the thin surface layer of the
oceans where light penetrates). Nearer to the continental margin increasing amounts of this organic input may
be derived from neritic (coastal) and terrestrial organic
material, in both particulate and dissolved form.
I shall not further consider non-photosynthetic,
chemosynthetic, production at hydrothermal vents and
methane seeps. Although estimates of the contribution
of these sources to global organic production are still
uncertain, they are unlikely to be more than trivial
and will not be further considered in this chapter (see
Chapter 4 for an account of chemosynthetically fuelled
communities in the deep sea). It is noted that these
chemosynthetic inputs occur directly at the deep-ocean
bed, and thus are not subject to the intense biological
reprocessing and mineralization in the upper water
column.
While food characteriztics strongly influence the
species composition of the community present, the
quantity and quality of food input to the seabed
community is the single most important determinant of
the abundance of populations in space and time, and
may also influence species richness (see Chapter 10).
Furthermore, because of the huge area covered by the
deep ocean, the dynamics of organic food consumption
and the recycling of this carbon by the allochthonous
system on the deep-sea bed is thought to be of
considerable importance to understanding of the global
carbon cycle, whose inputs are now significantly
augmented from combustion of fossil fuel.
Historical aspects
After discovery during the 19th century of life on
the floor of the deep ocean world-wide, there was
active discussion on how these remote populations are
sustained. The reports from the exploring voyages of
British navy ships Lightning and Porcupine in the
Northeast Atlantic and Mediterranean in the 1860s
(e.g., Jeffreys, 1869) and the famous world-encircling
voyage of H.M.S. Challenger in 1872–1876 (Thomson,
1880; Murray, 1895) address the transfer of organic
material as food to the bottom in the form of dead
surface-dwelling animals. These, and later expeditions
by ships of other nations, recognized the passive
sinking of organic particles as the main category
of food to the deep-sea ecosystem. Some of the
observations made, such as the quantitative importance
and seasonal nature of fast-sinking gelatinous plankton
to the deep ocean floor (Moseley, 1880), presaged
findings one hundred years later.
After World War II in the 1950s and 1960s there was
an extensive, world-wide program of deep-sea sampling by Russian workers. This prompted discussion
of nutritional sources and categorization of feeding
types in deep-sea benthic organisms (Sokolova, 1959).
The availability of new methods for measuring organic
carbon in organisms, in sediments and in sea water
then led to the first attempts to make a budget for
the marine organic-carbon cycle (Riley, 1970). At the
same time, new studies on the deep-sea benthos by
American workers in the 1960s led to fresh discussion
of the sources of nutrition for the remote community
313