THE DEEP ATLANTIC OCEAN
155
freshness of the sedimenting organic matter, which
depends in turn on the rapidity of transport from the
euphotic zone. Seasonal variation in bacterial numbers
and biomass have been recorded at the BIOTRANS
area, presumably in response to seasonal phytodetritus
deposition (Lochte, 1992), although such increases do
not always accompany microbial degradation of phytodetritus (Boetius and Lochte, 1994). Insights derived
from naturally or experimentally enriched samples,
however, are not applicable to bacterial populations in
oligotrophic deep-sea regions where activity is likely to
be much slower.
ANIMAL TRACES
The Atlantic seabed is covered with surficial sediment
features such as pits, burrows, mounds, tracks, fecal
casts and resting traces. Many of these result from
movement, burrowing, feeding, defecation or dwellingconstruction by benthic invertebrates and fishes (Hollister et al., 1975). Detailed surveys of these features have
been carried out in the Bay of Biscay (Mauviel and
Sibuet, 1985), on the Northwest Atlantic continental
margin (Hecker, 1994; Diaz et al., 1994), in the
Porcupine Seabight (de Vaugelas, 1989), the Porcupine
Abyssal Plain (Bett and Rice, 1993), the Cape Verde
Abyssal Plain (Bett et al., 1995) and the Bahama Outer
Ridge (Hollister et al., 1974).
Lebensspuren (traces of animal activity) often provide the main evidence for large organisms on abyssal
plains and elsewhere in the deep sea, and may be
particularly useful for quantifying buried megainfauna
(large animals living within the sediments). These
organisms, which are very difficult to sample using
conventional methods, potentially play a major role
in deep-sea community ecology and in the structuring
of the deep-sea sedimentary environment (RomeroWetzel and Gerlach, 1991; Bett et al., 1995). Bett
et al. (1995) have provided a survey of Lebensspuren
photographed on the Cape Verde Abyssal Plain using a
wide-angle survey photographic system (WASP) and a
camera attached to the epibenthic sledge. They found
that the density of traces on this oligotrophic abyssal
plain were two orders of magnitude greater than animal
densities estimated from the same photographic records
(8.72×10
−2 traces vs 5.2×10
−4 individuals m
−2 ). The
traces were dominated by various kinds of spoke
burrows, similar in form to those generally attributed
to echiurans. Bett et al. (1995) estimated that the abundance of the spoke-burrow producers is of the order
of 0.001 individuals m
−2 , considerably greater than
the density of surface-dwelling megabenthos. Similar
traces occur on the Madeira Abyssal Plain (Huggett,
1987). Young et al. (1985) found no strong correlation
of megafaunal diversity and trace diversity in the deep
Caribbean. However, because the persistence of these
features varies with both the physical environment
and biological activity (Gage and Tyler, 1991), it is
difficult to interpret animal densities directly from
quantification of Lebensspuren.
Sediment properties can influence the composition
of Lebensspuren. Huggett (1987) observed striking
differences in categories of feeding traces present
between areas of the Madeira Abyssal Plain underlain
by turbidite deposits and those underlain by pelagic
deposits. In particular, meandering traces, and small
spokes, were virtually confined to the turbidites, while
irregular traces were more common on the pelagic
deposits. Huggett (1987) attributed these differences to
the greater amounts of organic matter contained within
turbidite deposits. Thus, Lebensspuren may have the
potential to provide geologists with a simple visual
method for mapping the distribution of turbidites and
pelagic deposits.
DEMERSAL FISH
Merrett and Haedrich (1997) have provided an excellent overview of the biology of deep-sea demersal
fish; Haedrich (1997) described their distribution and
population ecology. Because some species are familiar
and commercially important, the biology of demersal
fish (e.g., their diets, reproduction and growth rates) is
better understood than that of megafaunal invertebrates,
particularly in the continental-slope settings that are
now accessible to fisheries. The abundance of fish and
invertebrates is not often compared. In the Porcupine
Seabight they have roughly comparable biomass values
and show a similar decrease with bathymetric depth
(Merrett and Haedrich, 1997, figs. 4.3, 4.4 therein).
On the Cape Verde Abyssal Plain, the density of the
invertebrate megafauna is about three times the density
of the fish (Bett et al., 1995).
The taxonomy and biogeography of bottom-dwelling
fish are probably better known in the North Atlantic
than in any other ocean. Regions like the Rockall
Trough are particularly well studied (e.g., Gordon
155
freshness of the sedimenting organic matter, which
depends in turn on the rapidity of transport from the
euphotic zone. Seasonal variation in bacterial numbers
and biomass have been recorded at the BIOTRANS
area, presumably in response to seasonal phytodetritus
deposition (Lochte, 1992), although such increases do
not always accompany microbial degradation of phytodetritus (Boetius and Lochte, 1994). Insights derived
from naturally or experimentally enriched samples,
however, are not applicable to bacterial populations in
oligotrophic deep-sea regions where activity is likely to
be much slower.
ANIMAL TRACES
The Atlantic seabed is covered with surficial sediment
features such as pits, burrows, mounds, tracks, fecal
casts and resting traces. Many of these result from
movement, burrowing, feeding, defecation or dwellingconstruction by benthic invertebrates and fishes (Hollister et al., 1975). Detailed surveys of these features have
been carried out in the Bay of Biscay (Mauviel and
Sibuet, 1985), on the Northwest Atlantic continental
margin (Hecker, 1994; Diaz et al., 1994), in the
Porcupine Seabight (de Vaugelas, 1989), the Porcupine
Abyssal Plain (Bett and Rice, 1993), the Cape Verde
Abyssal Plain (Bett et al., 1995) and the Bahama Outer
Ridge (Hollister et al., 1974).
Lebensspuren (traces of animal activity) often provide the main evidence for large organisms on abyssal
plains and elsewhere in the deep sea, and may be
particularly useful for quantifying buried megainfauna
(large animals living within the sediments). These
organisms, which are very difficult to sample using
conventional methods, potentially play a major role
in deep-sea community ecology and in the structuring
of the deep-sea sedimentary environment (RomeroWetzel and Gerlach, 1991; Bett et al., 1995). Bett
et al. (1995) have provided a survey of Lebensspuren
photographed on the Cape Verde Abyssal Plain using a
wide-angle survey photographic system (WASP) and a
camera attached to the epibenthic sledge. They found
that the density of traces on this oligotrophic abyssal
plain were two orders of magnitude greater than animal
densities estimated from the same photographic records
(8.72×10
−2 traces vs 5.2×10
−4 individuals m
−2 ). The
traces were dominated by various kinds of spoke
burrows, similar in form to those generally attributed
to echiurans. Bett et al. (1995) estimated that the abundance of the spoke-burrow producers is of the order
of 0.001 individuals m
−2 , considerably greater than
the density of surface-dwelling megabenthos. Similar
traces occur on the Madeira Abyssal Plain (Huggett,
1987). Young et al. (1985) found no strong correlation
of megafaunal diversity and trace diversity in the deep
Caribbean. However, because the persistence of these
features varies with both the physical environment
and biological activity (Gage and Tyler, 1991), it is
difficult to interpret animal densities directly from
quantification of Lebensspuren.
Sediment properties can influence the composition
of Lebensspuren. Huggett (1987) observed striking
differences in categories of feeding traces present
between areas of the Madeira Abyssal Plain underlain
by turbidite deposits and those underlain by pelagic
deposits. In particular, meandering traces, and small
spokes, were virtually confined to the turbidites, while
irregular traces were more common on the pelagic
deposits. Huggett (1987) attributed these differences to
the greater amounts of organic matter contained within
turbidite deposits. Thus, Lebensspuren may have the
potential to provide geologists with a simple visual
method for mapping the distribution of turbidites and
pelagic deposits.
DEMERSAL FISH
Merrett and Haedrich (1997) have provided an excellent overview of the biology of deep-sea demersal
fish; Haedrich (1997) described their distribution and
population ecology. Because some species are familiar
and commercially important, the biology of demersal
fish (e.g., their diets, reproduction and growth rates) is
better understood than that of megafaunal invertebrates,
particularly in the continental-slope settings that are
now accessible to fisheries. The abundance of fish and
invertebrates is not often compared. In the Porcupine
Seabight they have roughly comparable biomass values
and show a similar decrease with bathymetric depth
(Merrett and Haedrich, 1997, figs. 4.3, 4.4 therein).
On the Cape Verde Abyssal Plain, the density of the
invertebrate megafauna is about three times the density
of the fish (Bett et al., 1995).
The taxonomy and biogeography of bottom-dwelling
fish are probably better known in the North Atlantic
than in any other ocean. Regions like the Rockall
Trough are particularly well studied (e.g., Gordon