THE DEEP-SEA FLOOR: AN OVERVIEW
15
material can be displaced from the periphery of the
sample (Eckman and Thistle, 1988).
A variety of corers have been used historically
to sample macrofauna, meiofauna, and microbiota
(gravity corers, Smith–McIntyre grabs). The sampling
properties of these devices were not as good as those
of the box corer, deliberate corers, or submarine/ROV
samplers (see below). In particular, the bow wave was
more severe. Therefore, the data obtained with such
samplers must be interpreted with caution. Finally,
the collection of subsurface megafauna remains an
unsolved problem, but acoustical approaches (Jumars
et al., 1996) seem likely to be useful for some types of
measurements.
Research submarines and remotely operated
vehicles (ROVs)
A research submarine is comparable in size to a
delivery truck. Those in service typically carry a
pilot and one or two scientists in a pressure sphere
about 2 m in diameter. Surrounding the sphere is
equipment for life support, propulsion, ascent and
descent, and scientific purposes (manipulator arms,
cameras, specialized payload in a carrying basket)
(Heirtzler and Grassle, 1976). Research submarines
bring the ecologist into the deep sea and thereby
confer large benefits by correcting the tunnel vision
that deep-sea scientists acquire from the study of deepsea photographs. Further, research submarines permit
a wide range of ecological experiments. For example,
trays of defaunated sediment have been placed on
the seabed for study of colonization rates (Snelgrove
et al., 1992), and dyed sediment has been spread and
subsequently sampled for estimates of sediment mixing
rates (Levin et al., 1994).
Research submarines have limitations. For example,
positioning the vehicle and then removing the device
to be used (e.g., a corer) from its carrier, performing
the task, and returning the device to its carrier require
a substantial amount of time, so relatively few tasks
can be done during a dive. Also, because the vehicle is
large, maneuvering can be awkward, and experiments
are occasionally run over and ruined. Because of their
cost, few research submarines are in service, so dives
are rare. Much more research needs to be done than
can be accommodated.
Remotely operated vehicles (ROVs) are self-propelled
instrument packages. Some operate at the end of
a cable that provides power and hosts a two-way
communications link; others are untethered, carrying
their own power and recording images and data. The
instrument package consists of a propulsion unit,
sensors (particularly television), and, in some cases,
manipulator arms. Some ROVs are designed to “fly”
over the seabed. These ROVs tend to be used for
large-scale surveys, but some can be maneuvered with
precision and can inspect or sample centimeter-scale
targets (e.g., the MBARI ROV: Etchemendy and Davis,
1991). Other ROVs are bottom crawlers (e.g., the
Remote Underwater Manipulator: Thiel and Hessler,
1974) and are more suitable for seabed sampling and
experimentation.
The great advantage that ROVs have over research
submarines is endurance. Because the investigators are
on the support ship rather than in the vehicle, the ROV
does not have to be recovered each day to change crew
as does a research submarine. The time savings result
in far more ROV bottom time than research submarine
bottom time for each day at sea. Limitations of ROVs
include slow sampling and cumbersome maneuvering.
Also, there are substantial benefits to allowing deep-sea
scientists to come as close as possible to experiencing
the deep-sea environment. Scientists who have made
dives relate how their conception of the deep sea was
substantially changed by the experience, improving
their science.
Sensors
Knowledge of the chemical milieu in which deepsea-floor organisms live has increased markedly since
the introduction of microelectrode sensors. These
devices measure chemical parameters (oxygen, pH)
with a vertical resolution measured in millimeters.
Early measurements were made on recovered cores,
but free-vehicle technologies have been developed so
that measurements can be made in situ (see Reimers,
1987).
Other technologies
The devices discussed above are those that are in
common use. Many other devices have resulted in
important work but have not become common (see
Rowe and Sibuet, 1983). It is beyond the scope
of this chapter to present all these devices, but
two are conspicuous. The free-vehicle respirometer
(Smith et al., 1976), which measures oxygen utilization
by the benthic community, has been important in
15
material can be displaced from the periphery of the
sample (Eckman and Thistle, 1988).
A variety of corers have been used historically
to sample macrofauna, meiofauna, and microbiota
(gravity corers, Smith–McIntyre grabs). The sampling
properties of these devices were not as good as those
of the box corer, deliberate corers, or submarine/ROV
samplers (see below). In particular, the bow wave was
more severe. Therefore, the data obtained with such
samplers must be interpreted with caution. Finally,
the collection of subsurface megafauna remains an
unsolved problem, but acoustical approaches (Jumars
et al., 1996) seem likely to be useful for some types of
measurements.
Research submarines and remotely operated
vehicles (ROVs)
A research submarine is comparable in size to a
delivery truck. Those in service typically carry a
pilot and one or two scientists in a pressure sphere
about 2 m in diameter. Surrounding the sphere is
equipment for life support, propulsion, ascent and
descent, and scientific purposes (manipulator arms,
cameras, specialized payload in a carrying basket)
(Heirtzler and Grassle, 1976). Research submarines
bring the ecologist into the deep sea and thereby
confer large benefits by correcting the tunnel vision
that deep-sea scientists acquire from the study of deepsea photographs. Further, research submarines permit
a wide range of ecological experiments. For example,
trays of defaunated sediment have been placed on
the seabed for study of colonization rates (Snelgrove
et al., 1992), and dyed sediment has been spread and
subsequently sampled for estimates of sediment mixing
rates (Levin et al., 1994).
Research submarines have limitations. For example,
positioning the vehicle and then removing the device
to be used (e.g., a corer) from its carrier, performing
the task, and returning the device to its carrier require
a substantial amount of time, so relatively few tasks
can be done during a dive. Also, because the vehicle is
large, maneuvering can be awkward, and experiments
are occasionally run over and ruined. Because of their
cost, few research submarines are in service, so dives
are rare. Much more research needs to be done than
can be accommodated.
Remotely operated vehicles (ROVs) are self-propelled
instrument packages. Some operate at the end of
a cable that provides power and hosts a two-way
communications link; others are untethered, carrying
their own power and recording images and data. The
instrument package consists of a propulsion unit,
sensors (particularly television), and, in some cases,
manipulator arms. Some ROVs are designed to “fly”
over the seabed. These ROVs tend to be used for
large-scale surveys, but some can be maneuvered with
precision and can inspect or sample centimeter-scale
targets (e.g., the MBARI ROV: Etchemendy and Davis,
1991). Other ROVs are bottom crawlers (e.g., the
Remote Underwater Manipulator: Thiel and Hessler,
1974) and are more suitable for seabed sampling and
experimentation.
The great advantage that ROVs have over research
submarines is endurance. Because the investigators are
on the support ship rather than in the vehicle, the ROV
does not have to be recovered each day to change crew
as does a research submarine. The time savings result
in far more ROV bottom time than research submarine
bottom time for each day at sea. Limitations of ROVs
include slow sampling and cumbersome maneuvering.
Also, there are substantial benefits to allowing deep-sea
scientists to come as close as possible to experiencing
the deep-sea environment. Scientists who have made
dives relate how their conception of the deep sea was
substantially changed by the experience, improving
their science.
Sensors
Knowledge of the chemical milieu in which deepsea-floor organisms live has increased markedly since
the introduction of microelectrode sensors. These
devices measure chemical parameters (oxygen, pH)
with a vertical resolution measured in millimeters.
Early measurements were made on recovered cores,
but free-vehicle technologies have been developed so
that measurements can be made in situ (see Reimers,
1987).
Other technologies
The devices discussed above are those that are in
common use. Many other devices have resulted in
important work but have not become common (see
Rowe and Sibuet, 1983). It is beyond the scope
of this chapter to present all these devices, but
two are conspicuous. The free-vehicle respirometer
(Smith et al., 1976), which measures oxygen utilization
by the benthic community, has been important in