154
Lisa A. LEVIN and Andrew J. GOODAY
fairly well correlated with upwelling intensity, as
indicated by concentrations of chloroplastic pigments
in the sediments. In some regions away from the main
upwelling centers, densities are relatively low, despite
fairly high pigment concentrations. This discrepancy
may be due to the degradation of phytodetrital fluxes
during lateral advection by subsurface currents.
MICROBIAL PROCESSES
The earliest direct observations of bacterial populations
in the deep sea were made in the nineteenth century on
samples taken at 5100 m in the Mediterranean by the
French vessel Talisman (Certes, 1884), while the first
quantitative data on the rates of microbial activity were
obtained in the Pacific Ocean during the 1950s (Morita
and Zobell, 1955; Zobell and Morita, 1957a,b). During
the last three decades, however, work carried out in the
North Atlantic has contributed enormously to the rapid
development of ideas about deep-sea bacterial ecology
(Deming and Baross, 1993). In this section we highlight
some of these advances.
A landmark event in the history of modern deepsea microbiology was the sinking of the DSV
7 Alvin
off New England at a depth of 1540 m in 1968, and
the subsequent recovery of its relatively undegraded
lunch nearly a year later. Microbiologists interpreted
the lack of decomposition in the lunch to indicate
that metabolic rates of deep-sea microbes were much
slower than those in shallow water (Jannasch et al.,
1971). To a great extent, the results of this ‘experiment’
were misleading. The lack of substantial decomposition
can be largely explained by the way in which the
lunches were sealed, and therefore insulated from
the deep-sea scavengers and bacteria, rather than to
slow rates of deep-sea microbial activity (Sieburth
and Dietz, 1972). Nevertheless, the Alvin lunch incident strongly influenced the direction of deep-sea
biology, and initiated a generation of microbiological
experiments based on work with in situ free vehicles
or submersibles (Jannasch and Wirsen, 1973, 1983;
Wirsen and Jannasch, 1986).
An important theme in deep-sea microbiological
studies has been quantification of the abundance and
ecological role of bacteria. Much of this work has
been conducted in the North Atlantic (e.g., Deming,
1985; Lochte and Turley, 1988; Turley and Lochte,
1990; Meyer-Reil and K¨ oster, 1992; Lochte, 1992;
Deming and Yager, 1992; Deming and Baross, 1993;
Boetius and Lochte, 1994, 1996; Turley et al., 1995;
Turley, 2000; Turley and Dixon, 2002). Bacterial
densities and production tend to decrease with water
depth, but the correlation is weak. Flux of particulate
organic matter (POC) to the seafloor seems to exert
a stronger influence on bacterial populations. Both
biomass and the rate of utilization of dissolved
organic carbon (DOC) are particularly high at high
latitudes, where organic-matter inputs are substantial
and seasonally variable. The highest bacterial densities
ever recorded in deep-sea sediments were near the
HEBBLE site in the Northwest Atlantic, an area which
receives an abundant food supply from the activity
of currents (Thistle et al., 1985, 1991). The relation
observed between bacterial abundance and POC flux
is consistent with evidence which emerged during the
1980s that microbial processes can operate at much
faster rates than suggested by earlier studies, such as
the Alvin lunch ‘experiment’ (Deming, 1985; Lochte
and Turley, 1988; Gooday and Turley, 1990; Turley and
Lochte, 1990).
Microbial decomposition rates are often substantially
enhanced in food-rich microhabitats such as those
provided by vertebrate and invertebrate carcasses,
phytodetrital aggregates, benthic feces, animal burrows
and particularly within animal guts which are hot-spots
of barophilic activity. For example, experiments and
observations conducted within the past decade in the
North Atlantic (notably the BIOTRANS area), indicate
that freshly deposited phytodetritus is subjected to
intense microbial activity, and that remineralization
of the labile component occurs rapidly within a
period of about 5 days (e.g., Gooday and Turley,
1990; Poremba, 1994). Degradation is carried out by
extracellular hydrolytic enzymes (Boetius and Lochte,
1994), which originate from a mixture of barotolerant
bacteria conveyed from the upper water column on
sinking aggregates and from indigenous barophilic
bacteria (Lochte and Turley, 1988; Turley and Lochte,
1990; Turley et al., 1995). Small (3.5–6.0 mm long)
barophilic bodonid flagellates are also associated with
decomposing phytodetritus both in natural systems
(Lochte and Turley, 1988) and in experimental systems
(Turley et al., 1988), and may help to regulate the size
of associated bacterial populations.
Remineralization rates depend on the quality or
7 DSV : Deep Submergence Vehicle.
Lisa A. LEVIN and Andrew J. GOODAY
fairly well correlated with upwelling intensity, as
indicated by concentrations of chloroplastic pigments
in the sediments. In some regions away from the main
upwelling centers, densities are relatively low, despite
fairly high pigment concentrations. This discrepancy
may be due to the degradation of phytodetrital fluxes
during lateral advection by subsurface currents.
MICROBIAL PROCESSES
The earliest direct observations of bacterial populations
in the deep sea were made in the nineteenth century on
samples taken at 5100 m in the Mediterranean by the
French vessel Talisman (Certes, 1884), while the first
quantitative data on the rates of microbial activity were
obtained in the Pacific Ocean during the 1950s (Morita
and Zobell, 1955; Zobell and Morita, 1957a,b). During
the last three decades, however, work carried out in the
North Atlantic has contributed enormously to the rapid
development of ideas about deep-sea bacterial ecology
(Deming and Baross, 1993). In this section we highlight
some of these advances.
A landmark event in the history of modern deepsea microbiology was the sinking of the DSV
7 Alvin
off New England at a depth of 1540 m in 1968, and
the subsequent recovery of its relatively undegraded
lunch nearly a year later. Microbiologists interpreted
the lack of decomposition in the lunch to indicate
that metabolic rates of deep-sea microbes were much
slower than those in shallow water (Jannasch et al.,
1971). To a great extent, the results of this ‘experiment’
were misleading. The lack of substantial decomposition
can be largely explained by the way in which the
lunches were sealed, and therefore insulated from
the deep-sea scavengers and bacteria, rather than to
slow rates of deep-sea microbial activity (Sieburth
and Dietz, 1972). Nevertheless, the Alvin lunch incident strongly influenced the direction of deep-sea
biology, and initiated a generation of microbiological
experiments based on work with in situ free vehicles
or submersibles (Jannasch and Wirsen, 1973, 1983;
Wirsen and Jannasch, 1986).
An important theme in deep-sea microbiological
studies has been quantification of the abundance and
ecological role of bacteria. Much of this work has
been conducted in the North Atlantic (e.g., Deming,
1985; Lochte and Turley, 1988; Turley and Lochte,
1990; Meyer-Reil and K¨ oster, 1992; Lochte, 1992;
Deming and Yager, 1992; Deming and Baross, 1993;
Boetius and Lochte, 1994, 1996; Turley et al., 1995;
Turley, 2000; Turley and Dixon, 2002). Bacterial
densities and production tend to decrease with water
depth, but the correlation is weak. Flux of particulate
organic matter (POC) to the seafloor seems to exert
a stronger influence on bacterial populations. Both
biomass and the rate of utilization of dissolved
organic carbon (DOC) are particularly high at high
latitudes, where organic-matter inputs are substantial
and seasonally variable. The highest bacterial densities
ever recorded in deep-sea sediments were near the
HEBBLE site in the Northwest Atlantic, an area which
receives an abundant food supply from the activity
of currents (Thistle et al., 1985, 1991). The relation
observed between bacterial abundance and POC flux
is consistent with evidence which emerged during the
1980s that microbial processes can operate at much
faster rates than suggested by earlier studies, such as
the Alvin lunch ‘experiment’ (Deming, 1985; Lochte
and Turley, 1988; Gooday and Turley, 1990; Turley and
Lochte, 1990).
Microbial decomposition rates are often substantially
enhanced in food-rich microhabitats such as those
provided by vertebrate and invertebrate carcasses,
phytodetrital aggregates, benthic feces, animal burrows
and particularly within animal guts which are hot-spots
of barophilic activity. For example, experiments and
observations conducted within the past decade in the
North Atlantic (notably the BIOTRANS area), indicate
that freshly deposited phytodetritus is subjected to
intense microbial activity, and that remineralization
of the labile component occurs rapidly within a
period of about 5 days (e.g., Gooday and Turley,
1990; Poremba, 1994). Degradation is carried out by
extracellular hydrolytic enzymes (Boetius and Lochte,
1994), which originate from a mixture of barotolerant
bacteria conveyed from the upper water column on
sinking aggregates and from indigenous barophilic
bacteria (Lochte and Turley, 1988; Turley and Lochte,
1990; Turley et al., 1995). Small (3.5–6.0 mm long)
barophilic bodonid flagellates are also associated with
decomposing phytodetritus both in natural systems
(Lochte and Turley, 1988) and in experimental systems
(Turley et al., 1988), and may help to regulate the size
of associated bacterial populations.
Remineralization rates depend on the quality or
7 DSV : Deep Submergence Vehicle.