THE DEEP PACIFIC OCEAN FLOOR
213
deep Pacific (and of the deep ocean generally) can be
considered to be food-limited.
A variety of other factors may also be important
in dictating ecosystem structure in the deep Pacific
Ocean. These include hydrodynamic regime (especially
in canyons, on seamounts and beneath western boundary currents), bottom-water oxygen concentration (in
oxygen-minimum zones), availability of hard substrata
(in canyons, on seamounts), and hydrostatic pressure
(in trenches below roughly 6000 m depths). In extreme
cases, these factors may overwhelm the influence of the
flux of particulate organic carbon. For example, one
expects the structure of communities in the oxygenminimum zone to remain relatively constant as one
moves between sites characterized by different absolute
fluxes of particulate organic carbon, and the fauna of
manganese nodules exhibits great similarities across
the mesotrophic and oligotrophic abyss. Nonetheless,
within the low-energy, soft-sediment habitats that
really dominate the deep Pacific seafloor, the flux
of particulate organic carbon must be considered the
master variable influencing ecosystem structure.
Deep-sea benthic habitats of the Pacific have perhaps
been better studied than those in any other ocean;
nonetheless, there remain major gaps in the understanding of these ecosystems. Some of these gaps are
highlighted below.
(1) Complete energy budgets (including all major
outputs), as well as detailed biomass distributions
for all size classes (i.e., the microbes to megafauna),
are not available for any single benthic habitat in
the deep Pacific. Estimates of biomass production for
individual populations are almost wholly lacking. Thus,
there is still only very limited understanding of biomass
distributions and the roles of various biotic size classes
in the energetics of deep Pacific ecosystems.
(2) The nature, rates and variability of the
flux of particulate organic carbon to the deep-sea
floor are still very poorly quantified. In particular,
the flux of nekton falls has been measured in only
one site (the Santa Catalina Basin), where it appeared
to be quantitatively important. Deep-sea ecosystems
appear to be largely food-limited; until the nature
of food flux to the deep-sea floor is understood, the
key ecological and evolutionary forces shaping these
ecosystems cannot be elucidated.
(3) Knowledge of most ecological rates on the
deep-sea floor is extremely fragmentary. For example, the rates of a variety of processes including bioturbation, natural disturbance and succession, and patterns
of community recovery following anthropogenic disturbance (e.g., the dumping of sewage sludge and other
waste disposal, nodule mining) have been measured
at only a handful of locations (Tables 6.1 and 6.3).
Such information about rates is essential if one wishes
to predict the response of deep-sea ecosystems to
natural and anthropogenic change. Ecological intuition
suggests that the resistance and resilience of foodpoor, physically stable, deep-sea communities may be
lower than those of any other ecosystems on earth,
although even that is uncertain (for example, slope
habitats exhibit remarkable resilience in absorbing the
massive organic enrichment associated with whale
falls). Current ignorance of the rates of important
processes in some of the most extensive deep-sea
habitats is sobering. For example, to our knowledge,
rates of bioturbation, or of recolonization following
any type of disturbance, have never been measured
in oligotrophic abyssal habitats. This lack of rate data
from the oligotrophic abyss is particularly frustrating
because this region is enormous in size (it covers more
than 40% of the Pacific seafloor), and because it should
provide fascinating insights into ecosystem responses
to extraordinarily food-poor conditions (it is close to
being the most oligotrophic system in the biosphere).
Until these gaps are closed, one can only claim a
very incomplete understanding of the structure and
function of those ecosystems covering most of the
Earth’s solid surface.
ACKNOWLEDGMENTS
We thank Paul Tyler and John Gage for providing
the sabbatical hospitality that allowed the writing of
this chapter. We also are grateful to Paulo Sumida
for expertly rendering the figures. We are grateful to
a number of people for their helpful comments on
the manuscript, including P. Tyler, P. Sumida and an
anonymous reviewer. Original data presented in this
paper were collected with generous support from the
U.S. National Science Foundation and NOAA-NURC
Alaska.
REFERENCES
Aller, J.Y., 1989. Quantifying sediment disturbance by bottom
currents and its effect on benthic communities in a deep western
boundary zone. Deep-Sea Res., 36: 901−934.
213
deep Pacific (and of the deep ocean generally) can be
considered to be food-limited.
A variety of other factors may also be important
in dictating ecosystem structure in the deep Pacific
Ocean. These include hydrodynamic regime (especially
in canyons, on seamounts and beneath western boundary currents), bottom-water oxygen concentration (in
oxygen-minimum zones), availability of hard substrata
(in canyons, on seamounts), and hydrostatic pressure
(in trenches below roughly 6000 m depths). In extreme
cases, these factors may overwhelm the influence of the
flux of particulate organic carbon. For example, one
expects the structure of communities in the oxygenminimum zone to remain relatively constant as one
moves between sites characterized by different absolute
fluxes of particulate organic carbon, and the fauna of
manganese nodules exhibits great similarities across
the mesotrophic and oligotrophic abyss. Nonetheless,
within the low-energy, soft-sediment habitats that
really dominate the deep Pacific seafloor, the flux
of particulate organic carbon must be considered the
master variable influencing ecosystem structure.
Deep-sea benthic habitats of the Pacific have perhaps
been better studied than those in any other ocean;
nonetheless, there remain major gaps in the understanding of these ecosystems. Some of these gaps are
highlighted below.
(1) Complete energy budgets (including all major
outputs), as well as detailed biomass distributions
for all size classes (i.e., the microbes to megafauna),
are not available for any single benthic habitat in
the deep Pacific. Estimates of biomass production for
individual populations are almost wholly lacking. Thus,
there is still only very limited understanding of biomass
distributions and the roles of various biotic size classes
in the energetics of deep Pacific ecosystems.
(2) The nature, rates and variability of the
flux of particulate organic carbon to the deep-sea
floor are still very poorly quantified. In particular,
the flux of nekton falls has been measured in only
one site (the Santa Catalina Basin), where it appeared
to be quantitatively important. Deep-sea ecosystems
appear to be largely food-limited; until the nature
of food flux to the deep-sea floor is understood, the
key ecological and evolutionary forces shaping these
ecosystems cannot be elucidated.
(3) Knowledge of most ecological rates on the
deep-sea floor is extremely fragmentary. For example, the rates of a variety of processes including bioturbation, natural disturbance and succession, and patterns
of community recovery following anthropogenic disturbance (e.g., the dumping of sewage sludge and other
waste disposal, nodule mining) have been measured
at only a handful of locations (Tables 6.1 and 6.3).
Such information about rates is essential if one wishes
to predict the response of deep-sea ecosystems to
natural and anthropogenic change. Ecological intuition
suggests that the resistance and resilience of foodpoor, physically stable, deep-sea communities may be
lower than those of any other ecosystems on earth,
although even that is uncertain (for example, slope
habitats exhibit remarkable resilience in absorbing the
massive organic enrichment associated with whale
falls). Current ignorance of the rates of important
processes in some of the most extensive deep-sea
habitats is sobering. For example, to our knowledge,
rates of bioturbation, or of recolonization following
any type of disturbance, have never been measured
in oligotrophic abyssal habitats. This lack of rate data
from the oligotrophic abyss is particularly frustrating
because this region is enormous in size (it covers more
than 40% of the Pacific seafloor), and because it should
provide fascinating insights into ecosystem responses
to extraordinarily food-poor conditions (it is close to
being the most oligotrophic system in the biosphere).
Until these gaps are closed, one can only claim a
very incomplete understanding of the structure and
function of those ecosystems covering most of the
Earth’s solid surface.
ACKNOWLEDGMENTS
We thank Paul Tyler and John Gage for providing
the sabbatical hospitality that allowed the writing of
this chapter. We also are grateful to Paulo Sumida
for expertly rendering the figures. We are grateful to
a number of people for their helpful comments on
the manuscript, including P. Tyler, P. Sumida and an
anonymous reviewer. Original data presented in this
paper were collected with generous support from the
U.S. National Science Foundation and NOAA-NURC
Alaska.
REFERENCES
Aller, J.Y., 1989. Quantifying sediment disturbance by bottom
currents and its effect on benthic communities in a deep western
boundary zone. Deep-Sea Res., 36: 901−934.