THE DEEP ATLANTIC OCEAN
127
Canyon, studied with camera and trawl samples,
exhibited reduced abundances of some megafaunal
species relative to slope habitats, but that other taxa
were unique to the canyon. Haedrich et al. (1975,
1980) and Valentine et al. (1980), on the other hand,
found that megafaunal assemblages in Alvin, Hudson
and Oceanographer Canyons were similar to those on
nearby slopes. Houston and Haedrich (1984) studied
the macrofauna (>0.52 mm) within and outside Carson
submarine canyon (76–1129 m) on the Grand Banks.
They found no difference in abundance, biomass or
average body size (weight) inside or outside the canyon,
or with water depth. They noted unexpectedly low
abundance and biomass values, which they attributed
to low organic-carbon content of the sediment (0.3%).
Rowe et al. (1982), in studies of the Hudson Canyon
off New York, found that macrofaunal composition did
not differ inside the canyon from the adjacent slope.
Macrofaunal densities were higher within the canyon
head only at upper continental slope depths, most likely
a result of trapping of labile organic matter. Canyon
densities in deeper regions were comparable to those
on the outer slope.
Maciolek et al. (1987a) examined macrofauna within
and outside Lydonia Canyon (40º20
N, 67º40
W) at
550 and 2100 m during three cruises. At the shallower station, macrofauna were more abundant within
the canyon, owing in part to high densities of the
polychaetes Tharyx annulosus (32% of total fauna)
and Prionospio aluta (8.3% of total fauna). Over half
of the dominant species exhibited significant density
differences at the canyon stations. No macrofaunal differences between the canyon and slope were observed
at the deeper station, however.
A series of seven cruises examined the megafauna of
the canyons and slopes of the North Atlantic and MidAtlantic Bights, using bathymetric profiling, a towed
camera sled, and submersible observations (Hecker
et al., 1983). Lydonia Canyon in the North Atlantic
Bight was studied in detail. At most depths (300–
2100 m), densities of megafauna in the canyon were
greater than on the slope. Between 300 and 400 m this
difference resulted from dense assemblages of the sea
pen Pennatula aculeata and the brittle star Ophiura sp.
in the sediment-covered axis, to the coral Eunephthya
florida on cliffs and to the quill worm Hyalinoecia
artifex on the lower flanks. Between 500 and 1500 m
the canyon contained 38–614 individuals m
−2 , consisting largely of localized, dense populations of corals,
sponges and shrimps. The sponge Asbestopluma sp.
was especially abundant between 800 and 950 m.
Below 1500 m the brittle star Ophiomusium lymani
became very abundant in Lydonia Canyon and on the
slope. In the canyon, maximum O. lymani densities
occurred between 1750 and 1800 m, and the species
remained dominant to at least 2350 m. Other common
taxa within Lydonia Canyon and on the nearby slope
were the decapod crustaceans Cancer borealis, C. irroratus and Geryon quinquedens, and a several species of
hake (Urophycis spp.) and grenadier (Coryphaenoides
carpinus, C. rupestris and Nezumia aequalis/bairdii).
At least two species, the longfin hake (U. chesteri)
and the red crab (G. quinquedens), occurred at higher
abundances on the slope outside the canyon. Filter
feeders and scavengers dominated the canyon fauna at
depths less than 1000 m, while deposit feeders (mainly
Ophiomusium lymani) were dominant below 1500 m.
In general, Hecker et al. (1983) found faunal patterns
to be more complex and megafaunal assemblages less
cohesive within Lydonia Canyon than on the slope.
Baltimore Canyon (38º5
N, 73º40
W) in the MidAtlantic Bight was compared to two slope areas located
on the continental margin east of New Jersey (Hecker
et al., 1983). Consistent elevation of megafaunal
densities was not observed within Baltimore Canyon
relative to the comparison slope sites, as was the
case in Lydonia Canyon. However, densities from
Hendrickson Canyon were consistently higher than at
comparable depths on the slope (Hecker et al., 1983).
At depths greater than 500 m, dense aggregations of
anemones (Halcurias pilatus and Hormathia nodosa)
occurred on the canyon walls. Several dominants
on the slope, including a burrowing brittle star
(Amphilimna spp.), a sea pen (Stylatula elegans)
and a scleractinian (Desmosmilia lymani), were less
abundant in the canyon. In the Mid-Atlantic Bight,
as in the North Atlantic Bight, crabs and hake were
dominant within canyons and on the surrounding
slope, but they did not differentiate between these
habitats. The rattail Coryphaenoides rupestris was the
dominant grenadier within Baltimore and Hendrickson
Canyons, and appears to be a canyon ‘indicator’
species. The holothurian Peniagone sp. and the sea pen
Distichoptilum gracile were especially abundant within
Hendrickson Canyon. In Baltimore Canyon, scavengers
and carnivores dominated the megafauna above a depth
of 1400 m, filter feeders dominated between 1400 and
1600 m and deposit feeders dominated below 1600 m
(Hecker et al., 1983).
The extent to which canyon faunas appear distinct
127
Canyon, studied with camera and trawl samples,
exhibited reduced abundances of some megafaunal
species relative to slope habitats, but that other taxa
were unique to the canyon. Haedrich et al. (1975,
1980) and Valentine et al. (1980), on the other hand,
found that megafaunal assemblages in Alvin, Hudson
and Oceanographer Canyons were similar to those on
nearby slopes. Houston and Haedrich (1984) studied
the macrofauna (>0.52 mm) within and outside Carson
submarine canyon (76–1129 m) on the Grand Banks.
They found no difference in abundance, biomass or
average body size (weight) inside or outside the canyon,
or with water depth. They noted unexpectedly low
abundance and biomass values, which they attributed
to low organic-carbon content of the sediment (0.3%).
Rowe et al. (1982), in studies of the Hudson Canyon
off New York, found that macrofaunal composition did
not differ inside the canyon from the adjacent slope.
Macrofaunal densities were higher within the canyon
head only at upper continental slope depths, most likely
a result of trapping of labile organic matter. Canyon
densities in deeper regions were comparable to those
on the outer slope.
Maciolek et al. (1987a) examined macrofauna within
and outside Lydonia Canyon (40º20
N, 67º40
W) at
550 and 2100 m during three cruises. At the shallower station, macrofauna were more abundant within
the canyon, owing in part to high densities of the
polychaetes Tharyx annulosus (32% of total fauna)
and Prionospio aluta (8.3% of total fauna). Over half
of the dominant species exhibited significant density
differences at the canyon stations. No macrofaunal differences between the canyon and slope were observed
at the deeper station, however.
A series of seven cruises examined the megafauna of
the canyons and slopes of the North Atlantic and MidAtlantic Bights, using bathymetric profiling, a towed
camera sled, and submersible observations (Hecker
et al., 1983). Lydonia Canyon in the North Atlantic
Bight was studied in detail. At most depths (300–
2100 m), densities of megafauna in the canyon were
greater than on the slope. Between 300 and 400 m this
difference resulted from dense assemblages of the sea
pen Pennatula aculeata and the brittle star Ophiura sp.
in the sediment-covered axis, to the coral Eunephthya
florida on cliffs and to the quill worm Hyalinoecia
artifex on the lower flanks. Between 500 and 1500 m
the canyon contained 38–614 individuals m
−2 , consisting largely of localized, dense populations of corals,
sponges and shrimps. The sponge Asbestopluma sp.
was especially abundant between 800 and 950 m.
Below 1500 m the brittle star Ophiomusium lymani
became very abundant in Lydonia Canyon and on the
slope. In the canyon, maximum O. lymani densities
occurred between 1750 and 1800 m, and the species
remained dominant to at least 2350 m. Other common
taxa within Lydonia Canyon and on the nearby slope
were the decapod crustaceans Cancer borealis, C. irroratus and Geryon quinquedens, and a several species of
hake (Urophycis spp.) and grenadier (Coryphaenoides
carpinus, C. rupestris and Nezumia aequalis/bairdii).
At least two species, the longfin hake (U. chesteri)
and the red crab (G. quinquedens), occurred at higher
abundances on the slope outside the canyon. Filter
feeders and scavengers dominated the canyon fauna at
depths less than 1000 m, while deposit feeders (mainly
Ophiomusium lymani) were dominant below 1500 m.
In general, Hecker et al. (1983) found faunal patterns
to be more complex and megafaunal assemblages less
cohesive within Lydonia Canyon than on the slope.
Baltimore Canyon (38º5
N, 73º40
W) in the MidAtlantic Bight was compared to two slope areas located
on the continental margin east of New Jersey (Hecker
et al., 1983). Consistent elevation of megafaunal
densities was not observed within Baltimore Canyon
relative to the comparison slope sites, as was the
case in Lydonia Canyon. However, densities from
Hendrickson Canyon were consistently higher than at
comparable depths on the slope (Hecker et al., 1983).
At depths greater than 500 m, dense aggregations of
anemones (Halcurias pilatus and Hormathia nodosa)
occurred on the canyon walls. Several dominants
on the slope, including a burrowing brittle star
(Amphilimna spp.), a sea pen (Stylatula elegans)
and a scleractinian (Desmosmilia lymani), were less
abundant in the canyon. In the Mid-Atlantic Bight,
as in the North Atlantic Bight, crabs and hake were
dominant within canyons and on the surrounding
slope, but they did not differentiate between these
habitats. The rattail Coryphaenoides rupestris was the
dominant grenadier within Baltimore and Hendrickson
Canyons, and appears to be a canyon ‘indicator’
species. The holothurian Peniagone sp. and the sea pen
Distichoptilum gracile were especially abundant within
Hendrickson Canyon. In Baltimore Canyon, scavengers
and carnivores dominated the megafauna above a depth
of 1400 m, filter feeders dominated between 1400 and
1600 m and deposit feeders dominated below 1600 m
(Hecker et al., 1983).
The extent to which canyon faunas appear distinct