124
Lisa A. LEVIN and Andrew J. GOODAY
made under the auspices of the United States Minerals
Management Service, which is charged with evaluating
natural resources (e.g., hydrocarbons) and the impact
of exploiting these. These reports divide the ASCAR
region into the North, Mid and South Atlantic Bights
(NAB, MAB and SAB, respectively), covering the
United States margin from Georgia to Canada.
Gay Head–Bermuda transect
Historically, perhaps the most important study of
Atlantic deep-sea infaunal communities was carried
out by Sanders, Hessler and coworkers (Sanders et al.,
1965). They sampled sediments along a transect from
the Massachusetts shelf (20 m) to Bermuda (1000 m),
encompassing the intervening slope, rise and abyssal
environments; this is now referred to as the Gay Head–
Bermuda transect. Quantitative samples were taken
with an anchor dredge and washed through a 0.42 mm
mesh. They revealed much higher faunal densities
and diversity than expected (Hessler and Sanders,
1967), and initiated a persistent fascination with the
quantification and explanation of high diversity in the
deep sea (Rex, 1983; Grassle, 1989; Rex et al., 1997).
Macrofaunal densities decreased with both depth and
distance from land (Sanders et al., 1965; Hessler and
Sanders, 1967; Sanders and Hessler, 1969), and each
region along the transect was found to support characteristic faunal densities (individuals m
−2 ): the outer
continental shelf 6000–13 000; the upper slope 6000–
23 000; the lower slope 1500–3000, the continental rise
500–1200; the abyss beneath the Gulf Stream 150–
270; the abyss in the Sargasso Sea 30–130; the lower
Bermuda Slope 120–300 and the upper Bermuda slope
500–750 (Sanders et al., 1965). Polychaetes formed
34–84%, crustaceans 3.5–50% and bivalves 1–24% of
these faunal assemblages. The best-represented polychaete families were the Ampharetidae, Maldanidae,
Paraonidae, Phyllodocidae, Spionidae and Syllidae,
which together accounted for 88 of the 266 polychaete
species present (Sanders et al., 1965). Bivalves were
mainly Eulamellibranchiata and Protobranchiata (93%
of total). No consistent relationship was observed
between animal densities and the organic-carbon or
nitrogen content of the sediments, and it was noted
that some of the highest densities occurred on the
upper slope where organic-carbon values were low
(Sanders et al., 1965). Sanders et al. (1965) proposed
that the absence of correlation was related to the
refractory nature of sedimentary organic matter, an idea
substantiated by later studies on the northwest margin
(references in Diaz et al., 1994).
Epibenthic sled samples taken along the Gay Head–
Bermuda transect yielded a spectrum of species
different from that given by the anchor dredge, but
substantiated the finding of high faunal diversity
in individual samples (Hessler and Sanders, 1967;
Sanders and Hessler, 1969). Along the transect, sharp
faunal breaks were observed for polychaetes, bivalves
and crustaceans at the shelf–slope boundary (100 to
300 m), a region taken as the upper limit of the deepsea benthos in this part of the Atlantic. Despite an
absence of abrupt boundaries at bathyal or abyssal
depths, Sanders and Hessler (1969) considered depth
to be a primary determinant of species composition.
They pointed out that, while 48% of bivalve species
were shared between a 1400-m station on the Gay
Head–Bermuda transect and a 1700-m station off
West Africa, an 800-m change in depth on the
Northwest Atlantic margin (along the Gay Head–
Bermuda transect) produced much greater differences
in species composition. Sanders and Hessler (1969)
also argued that depth change has a greater impact
on densities than distance from land. For example,
densities at their 4500 m and 5000 m stations were less
than at 200 m by a factor of 50–390, despite surface
productivity being half as great at the deeper stations.
Studies of the respiration of the benthic community,
conducted along the Gay Head–Bermuda transect with
grab respirometers (Smith, 1978), indicated decreasing
oxygen consumption by the sediment community
with increasing water depth and distance from shore
(Smith and Hinga, 1983). Respiration varied by a
factor of 25 from the shallowest station (1850 m)
to the deepest (5200 m). Smith (1978) formulated a
predictive equation for sediment-community oxygen
consumption (SCOC) which explained 92.4% of the
variation in measurements. Depth alone accounted
for 83.1% of this, with sediment nitrogen content,
C:N ratio, faunal biomass and water temperature also
contributing.
Nova Scotia rise
The Nova Scotia rise is the best-studied high-energy
habitat in the deep Atlantic Ocean. An area centered
around 40º27
N, 62º20
W (4600 to 4800 m) experiences episodic, intense sediment-transport events. This
was the site of the High Energy Benthic Boundary
Layer Experiment (HEBBLE), which focused on the
physical aspects, sediment transport and biological dynamics of this energetic benthic environment. Currents
within 59 m of the seabed, measured over a 4.5 year
Lisa A. LEVIN and Andrew J. GOODAY
made under the auspices of the United States Minerals
Management Service, which is charged with evaluating
natural resources (e.g., hydrocarbons) and the impact
of exploiting these. These reports divide the ASCAR
region into the North, Mid and South Atlantic Bights
(NAB, MAB and SAB, respectively), covering the
United States margin from Georgia to Canada.
Gay Head–Bermuda transect
Historically, perhaps the most important study of
Atlantic deep-sea infaunal communities was carried
out by Sanders, Hessler and coworkers (Sanders et al.,
1965). They sampled sediments along a transect from
the Massachusetts shelf (20 m) to Bermuda (1000 m),
encompassing the intervening slope, rise and abyssal
environments; this is now referred to as the Gay Head–
Bermuda transect. Quantitative samples were taken
with an anchor dredge and washed through a 0.42 mm
mesh. They revealed much higher faunal densities
and diversity than expected (Hessler and Sanders,
1967), and initiated a persistent fascination with the
quantification and explanation of high diversity in the
deep sea (Rex, 1983; Grassle, 1989; Rex et al., 1997).
Macrofaunal densities decreased with both depth and
distance from land (Sanders et al., 1965; Hessler and
Sanders, 1967; Sanders and Hessler, 1969), and each
region along the transect was found to support characteristic faunal densities (individuals m
−2 ): the outer
continental shelf 6000–13 000; the upper slope 6000–
23 000; the lower slope 1500–3000, the continental rise
500–1200; the abyss beneath the Gulf Stream 150–
270; the abyss in the Sargasso Sea 30–130; the lower
Bermuda Slope 120–300 and the upper Bermuda slope
500–750 (Sanders et al., 1965). Polychaetes formed
34–84%, crustaceans 3.5–50% and bivalves 1–24% of
these faunal assemblages. The best-represented polychaete families were the Ampharetidae, Maldanidae,
Paraonidae, Phyllodocidae, Spionidae and Syllidae,
which together accounted for 88 of the 266 polychaete
species present (Sanders et al., 1965). Bivalves were
mainly Eulamellibranchiata and Protobranchiata (93%
of total). No consistent relationship was observed
between animal densities and the organic-carbon or
nitrogen content of the sediments, and it was noted
that some of the highest densities occurred on the
upper slope where organic-carbon values were low
(Sanders et al., 1965). Sanders et al. (1965) proposed
that the absence of correlation was related to the
refractory nature of sedimentary organic matter, an idea
substantiated by later studies on the northwest margin
(references in Diaz et al., 1994).
Epibenthic sled samples taken along the Gay Head–
Bermuda transect yielded a spectrum of species
different from that given by the anchor dredge, but
substantiated the finding of high faunal diversity
in individual samples (Hessler and Sanders, 1967;
Sanders and Hessler, 1969). Along the transect, sharp
faunal breaks were observed for polychaetes, bivalves
and crustaceans at the shelf–slope boundary (100 to
300 m), a region taken as the upper limit of the deepsea benthos in this part of the Atlantic. Despite an
absence of abrupt boundaries at bathyal or abyssal
depths, Sanders and Hessler (1969) considered depth
to be a primary determinant of species composition.
They pointed out that, while 48% of bivalve species
were shared between a 1400-m station on the Gay
Head–Bermuda transect and a 1700-m station off
West Africa, an 800-m change in depth on the
Northwest Atlantic margin (along the Gay Head–
Bermuda transect) produced much greater differences
in species composition. Sanders and Hessler (1969)
also argued that depth change has a greater impact
on densities than distance from land. For example,
densities at their 4500 m and 5000 m stations were less
than at 200 m by a factor of 50–390, despite surface
productivity being half as great at the deeper stations.
Studies of the respiration of the benthic community,
conducted along the Gay Head–Bermuda transect with
grab respirometers (Smith, 1978), indicated decreasing
oxygen consumption by the sediment community
with increasing water depth and distance from shore
(Smith and Hinga, 1983). Respiration varied by a
factor of 25 from the shallowest station (1850 m)
to the deepest (5200 m). Smith (1978) formulated a
predictive equation for sediment-community oxygen
consumption (SCOC) which explained 92.4% of the
variation in measurements. Depth alone accounted
for 83.1% of this, with sediment nitrogen content,
C:N ratio, faunal biomass and water temperature also
contributing.
Nova Scotia rise
The Nova Scotia rise is the best-studied high-energy
habitat in the deep Atlantic Ocean. An area centered
around 40º27
N, 62º20
W (4600 to 4800 m) experiences episodic, intense sediment-transport events. This
was the site of the High Energy Benthic Boundary
Layer Experiment (HEBBLE), which focused on the
physical aspects, sediment transport and biological dynamics of this energetic benthic environment. Currents
within 59 m of the seabed, measured over a 4.5 year