THE DEEP ATLANTIC OCEAN
123
et al. (1994) reported that sediment oxygen consumption at an oligotrophic site near Bermuda (4400 m water
depth) was nearly constant between March 1989 and
October 1992, despite strong seasonal variations in the
organic-matter flux to the seafloor.
There is evidence for changes in the abundance and
biomass of particular size classes and taxa following
organic-matter inputs. In a detailed study of the
BIOTRANS area (4550 m depth) of the Northeast
Atlantic, Pfannkuche (1992, 1993) and Lochte (1992)
found: (a) a doubling of bacterial biomass between
March and July, and (b) a switch from dominance
of the meiofaunal fraction by metazoans in March
and May to dominance by Foraminifera in July and
September. Small barophilic flagellates also thrive
within organic aggregates (Lochte and Turley, 1988).
Thus, the response to phytodetritus at the BIOTRANS
site is accounted for mainly by Bacteria and protozoans
(see also Pfannkuche and Soltwedel, 1998). Among
benthic Foraminifera, the immediate response seems
to be largely confined to certain opportunistic species
which live mainly in the phytodetrital layer (Gooday,
1988, 1993, 1996b) and undergo rapid population
increases during the summer (Gooday and Lambshead,
1989; Gooday and Turley, 1990). The opportunists
include Alabaminella weddellensis and Epistominella
exigua, both calcareous forms, and the allogromiid
Tinogullmia riemanni.
A link between food pulses and metazoan population
dynamics has proved more difficult to establish. Unlike
Foraminifera and Bacteria, the metazoan meiofauna
and macrofauna exhibited no significant increase in
either numbers or biomass following phytodetrital
deposition at the abyssal BIOTRANS site (Pfannkuche,
1992, 1993) and in the bathyal Porcupine Seabight
(Gooday et al., 1996). There is some evidence from the
Hebridean margin, however, that meiofaunal densities
increase during the summer (Mitchell et al., 1996).
Similar results have been obtained in the bathyal
Mediterranean (de Bov´ ee et al., 1990). However, direct
evidence that phytodetritus may influence growth rates
is provided by BATHYSNAP photographs showing a
specimen of the barnacle Poecilasma kaempferi growing more quickly during and following the deposition
of phytodetritus on the Goban Spur (1520 m depth)
than prior to the flux event (Lampitt, 1990). Some
echinoderms certainly feed on phytodetritus. Pigment
analysis of the gut contents of certain holothurian
species suggests that they consume phytodetritus almost exclusively when it is present on the seafloor
(Billett et al., 1988; Lauerman et al., 1997). There
is good evidence from gut contents and sea-floor
photographs that the echinoid Echinus affinis feeds
on fresh phytodetrital deposits (Campos-Creasey et al.,
1994), and that this triggers the seasonal growth
and reproduction reported in this species (Tyler and
Gage, 1984; Gage and Tyler, 1985). Seasonal growth
and reproduction reported in a range of other North
Atlantic deep-sea invertebrates (sponges, actiniarians,
brachiopods, protobranch bivalves, echinoids, asteroids, ophiuroids, spider crabs and hermit crabs) may
also be linked to seasonality in food supply, although
the evidence is largely circumstantial (Tyler, 1986,
1988, 1995; Gooday and Turley, 1990; Gage and Tyler,
1991; Van-Pra¨ et, 1990; Witte, 1996).
REGIONAL DESCRIPTIONS
The Northwest Atlantic continental margin
The Atlantic continental slope and rise (ASCAR
region; 28–42ºN, 200–4000 m water depth) off the
eastern United States has been studied extensively
(Milliman and Wright, 1987). Several large programs
(Table 5.1) have focused on aspects of carbon cycling and benthic biological patterns on the slope,
though much additional work has taken place on the
continental shelf. A dominant physical feature is the
warm Gulf Stream, which flows north from the Florida
Strait along the slope and then diverges eastwards off
Cape Hatteras. The western Boundary undercurrent,
associated with North Atlantic deep water, flows
southwest along the entire rise below about 2000 m.
Colder coastal and slope water, derived from various
sources, occurs generally inshore of the Gulf Stream
(Schmitz et al., 1987). The direct influence of the Gulf
Stream on the bottom can be detected to a depth of
over 600 m in some places. Both cold-core (cyclonic)
and warm-core (anticyclonic) rings, associated with the
Gulf Stream, introduce water with different properties
into the major ASCAR water masses. However, ring
effects are concentrated in the upper 1000 m (Schmitz
et al., 1987).
General discussions of the biological communities
of the ASCAR region can be found in Hessler and
Sanders (1967), Hecker et al. (1983), Blake et al.
(1985, 1987), Maciolek et al. (1987a,b), Wiebe et al.
(1987), and articles within Diaz et al. (1994). Many
of these reports are the result of extensive surveys
123
et al. (1994) reported that sediment oxygen consumption at an oligotrophic site near Bermuda (4400 m water
depth) was nearly constant between March 1989 and
October 1992, despite strong seasonal variations in the
organic-matter flux to the seafloor.
There is evidence for changes in the abundance and
biomass of particular size classes and taxa following
organic-matter inputs. In a detailed study of the
BIOTRANS area (4550 m depth) of the Northeast
Atlantic, Pfannkuche (1992, 1993) and Lochte (1992)
found: (a) a doubling of bacterial biomass between
March and July, and (b) a switch from dominance
of the meiofaunal fraction by metazoans in March
and May to dominance by Foraminifera in July and
September. Small barophilic flagellates also thrive
within organic aggregates (Lochte and Turley, 1988).
Thus, the response to phytodetritus at the BIOTRANS
site is accounted for mainly by Bacteria and protozoans
(see also Pfannkuche and Soltwedel, 1998). Among
benthic Foraminifera, the immediate response seems
to be largely confined to certain opportunistic species
which live mainly in the phytodetrital layer (Gooday,
1988, 1993, 1996b) and undergo rapid population
increases during the summer (Gooday and Lambshead,
1989; Gooday and Turley, 1990). The opportunists
include Alabaminella weddellensis and Epistominella
exigua, both calcareous forms, and the allogromiid
Tinogullmia riemanni.
A link between food pulses and metazoan population
dynamics has proved more difficult to establish. Unlike
Foraminifera and Bacteria, the metazoan meiofauna
and macrofauna exhibited no significant increase in
either numbers or biomass following phytodetrital
deposition at the abyssal BIOTRANS site (Pfannkuche,
1992, 1993) and in the bathyal Porcupine Seabight
(Gooday et al., 1996). There is some evidence from the
Hebridean margin, however, that meiofaunal densities
increase during the summer (Mitchell et al., 1996).
Similar results have been obtained in the bathyal
Mediterranean (de Bov´ ee et al., 1990). However, direct
evidence that phytodetritus may influence growth rates
is provided by BATHYSNAP photographs showing a
specimen of the barnacle Poecilasma kaempferi growing more quickly during and following the deposition
of phytodetritus on the Goban Spur (1520 m depth)
than prior to the flux event (Lampitt, 1990). Some
echinoderms certainly feed on phytodetritus. Pigment
analysis of the gut contents of certain holothurian
species suggests that they consume phytodetritus almost exclusively when it is present on the seafloor
(Billett et al., 1988; Lauerman et al., 1997). There
is good evidence from gut contents and sea-floor
photographs that the echinoid Echinus affinis feeds
on fresh phytodetrital deposits (Campos-Creasey et al.,
1994), and that this triggers the seasonal growth
and reproduction reported in this species (Tyler and
Gage, 1984; Gage and Tyler, 1985). Seasonal growth
and reproduction reported in a range of other North
Atlantic deep-sea invertebrates (sponges, actiniarians,
brachiopods, protobranch bivalves, echinoids, asteroids, ophiuroids, spider crabs and hermit crabs) may
also be linked to seasonality in food supply, although
the evidence is largely circumstantial (Tyler, 1986,
1988, 1995; Gooday and Turley, 1990; Gage and Tyler,
1991; Van-Pra¨ et, 1990; Witte, 1996).
REGIONAL DESCRIPTIONS
The Northwest Atlantic continental margin
The Atlantic continental slope and rise (ASCAR
region; 28–42ºN, 200–4000 m water depth) off the
eastern United States has been studied extensively
(Milliman and Wright, 1987). Several large programs
(Table 5.1) have focused on aspects of carbon cycling and benthic biological patterns on the slope,
though much additional work has taken place on the
continental shelf. A dominant physical feature is the
warm Gulf Stream, which flows north from the Florida
Strait along the slope and then diverges eastwards off
Cape Hatteras. The western Boundary undercurrent,
associated with North Atlantic deep water, flows
southwest along the entire rise below about 2000 m.
Colder coastal and slope water, derived from various
sources, occurs generally inshore of the Gulf Stream
(Schmitz et al., 1987). The direct influence of the Gulf
Stream on the bottom can be detected to a depth of
over 600 m in some places. Both cold-core (cyclonic)
and warm-core (anticyclonic) rings, associated with the
Gulf Stream, introduce water with different properties
into the major ASCAR water masses. However, ring
effects are concentrated in the upper 1000 m (Schmitz
et al., 1987).
General discussions of the biological communities
of the ASCAR region can be found in Hessler and
Sanders (1967), Hecker et al. (1983), Blake et al.
(1985, 1987), Maciolek et al. (1987a,b), Wiebe et al.
(1987), and articles within Diaz et al. (1994). Many
of these reports are the result of extensive surveys