THE DEEP ATLANTIC OCEAN
137
than during April before its arrival. In contrast, few
seasonal changes were observed among the metazoan
meiofauna at this site (Gooday et al., 1996).
Goban Spur: The Goban Spur is a gently sloping
stepped platform which, together with the Meriadzek
Terrace (a plateau-like feature on the continental
margin to the southeast of the Goban Spur; see
Fig. 5.1), forms the southeastern flank of the Porcupine
Seabight. This region was studied intensively as part
of the OMEX project funded by the European Union,
which addressed the role of the Northwest European
continental margin in the global carbon cycle (van
Weering et al., 1998).
Total benthic biomass on the Goban Spur was
dominated by small organisms: Bacteria, Fungi, flagellates, Foraminifera, and small metazoan meiofauna.
The percentage contribution of these groups to the
total benthic biomass increased with water depth
from 90% on the shelf to 97–98% at bathyal and
abyssal depths (Pfannkuche and Soltwedel, 1998).
Soltwedel et al. (1996) studied trends in the metazoan
meiofauna along a transect extending down the Goban
Spur and onto the Porcupine Abyssal Plain (182–
4470 m). Abundances (individuals cm
−2 ) varied as
follows: 33.5 (182 m), 38.1 (410 m), 19.1 (1013 m),
6.6 (2084 m), 4.3 (3552 m), 6.4 (3889 m), 12.4 (4470 m).
Nematodes made up between 66% (at 182 m) and
93% (at 3552 m) of the fauna and, below depths
of 2000 m, showed a clear decrease in size with
increasing bathymetric depth, as observed previously
by Pfannkuche (1985) in the Porcupine Seabight and
Soetaert and Heip (1989) in the Mediterranean. These
observations support the hypothesis of Thiel (1975)
that organisms tend to become smaller with increasing
bathymetric depth as a result of food limitation.
Flach and Heip (1996a) analysed macrofauna (>500
mm; no. ind. m
−2 ) in box cores taken along a similar
transect (208–4470 m) during October 1993, May 1994
and August 1995, and related the differences observed
to seasonal and interannual variations in organicmatter inputs. Flach and Heip (1996b) have reported
on the vertical distribution of macrofauna within the
upper 15 cm of sediment in the May 1994 samples.
One of the main findings of these studies is that
there are clear seasonal and interannual variations
in the macrofauna on the Goban Spur only above
about 1500 m depth. Macrofaunal densities decreased
exponentially with increasing bathymetric depth, but
they also showed substantial seasonal and interannual
differences. In particular, densities were significantly
higher on the upper part of the slope (down to
1500 m) during May than in August and October,
mainly as a result of the presence of large numbers of
juvenile echinoderms including the echinoid Echinus
affinis and the ophiuroid Ophiocten gracilis, both
seasonal breeders. These fluctuations probably reflect
interannular differences in the intensity of phytodetrital
pulses. Polychaetes were always the most important
macrofaunal taxon. Their numbers declined fairly regularly along the transect, and were significantly higher
at the two shallowest stations (208–231 m, 670–693 m)
during May. Crustaceans were most abundant at midslope depths (670–2256 m), significantly more so in
August. Biomass (mg m
−2 ) also tended to decline with
depth, but was consistently higher (1021) at 1034 m
(station B), owing to the predominance of relatively
large animals, and low (1425) at 1457 m (station II)
where the animals were relatively small. Sedimentary
organic carbon peaked at station B, suggesting that this
site received substantial inputs of labile phytodetritus.
Biomass values were somewhat higher in May at the
three shallowest stations (208–1034 m) and higher in
August at mid-slope stations (1425–2256 m), but these
seasonal differences were not significant. Macrofaunal
community respiration rates, estimated from individual
weights and biomass values, were high in May between
208 m and 1034 m, but much lower at the deeper
stations. At mid-slope depths (2200 m), however, rates
were higher in August than in May. Between 40% and
80% of the macrofauna occurred in the 0–1 cm layer of
sediment and the stations of intermediate depth (670 m,
1034 m and 1425 m) showed the highest proportions
within this upper layer.
The numerical density of the megafauna undergoes a steady decrease along the OMEX transect,
but biomass values are more irregular (Duineveld
et al., 1997). Low values are found around the shelf
break (200 m) and upper slope (700 m) (1913 and
1914 g wet weight 1000 m
−2 , respectively) and Pendragon Escarpment (2200 m; 1188 g 1000 m
−2 ), while
the highest values occur at 1450 m (4076 g 1000 m
−2 )
and 3650 m (3789 g 1000 m
−2 ). These irregularities
reflect the changing taxonomic composition of the
megafauna, which is dominated at different depths
by crinoids (200 m), echinoids (700 m), holothurians
(100 m, 3650 m, 4500 m) and poriferans (1450 m).
Among the megafauna, macrofauna and Foraminifera
(>150 mm fraction), the proportion of deposit feeders
generally increased with increasing water depth across
137
than during April before its arrival. In contrast, few
seasonal changes were observed among the metazoan
meiofauna at this site (Gooday et al., 1996).
Goban Spur: The Goban Spur is a gently sloping
stepped platform which, together with the Meriadzek
Terrace (a plateau-like feature on the continental
margin to the southeast of the Goban Spur; see
Fig. 5.1), forms the southeastern flank of the Porcupine
Seabight. This region was studied intensively as part
of the OMEX project funded by the European Union,
which addressed the role of the Northwest European
continental margin in the global carbon cycle (van
Weering et al., 1998).
Total benthic biomass on the Goban Spur was
dominated by small organisms: Bacteria, Fungi, flagellates, Foraminifera, and small metazoan meiofauna.
The percentage contribution of these groups to the
total benthic biomass increased with water depth
from 90% on the shelf to 97–98% at bathyal and
abyssal depths (Pfannkuche and Soltwedel, 1998).
Soltwedel et al. (1996) studied trends in the metazoan
meiofauna along a transect extending down the Goban
Spur and onto the Porcupine Abyssal Plain (182–
4470 m). Abundances (individuals cm
−2 ) varied as
follows: 33.5 (182 m), 38.1 (410 m), 19.1 (1013 m),
6.6 (2084 m), 4.3 (3552 m), 6.4 (3889 m), 12.4 (4470 m).
Nematodes made up between 66% (at 182 m) and
93% (at 3552 m) of the fauna and, below depths
of 2000 m, showed a clear decrease in size with
increasing bathymetric depth, as observed previously
by Pfannkuche (1985) in the Porcupine Seabight and
Soetaert and Heip (1989) in the Mediterranean. These
observations support the hypothesis of Thiel (1975)
that organisms tend to become smaller with increasing
bathymetric depth as a result of food limitation.
Flach and Heip (1996a) analysed macrofauna (>500
mm; no. ind. m
−2 ) in box cores taken along a similar
transect (208–4470 m) during October 1993, May 1994
and August 1995, and related the differences observed
to seasonal and interannual variations in organicmatter inputs. Flach and Heip (1996b) have reported
on the vertical distribution of macrofauna within the
upper 15 cm of sediment in the May 1994 samples.
One of the main findings of these studies is that
there are clear seasonal and interannual variations
in the macrofauna on the Goban Spur only above
about 1500 m depth. Macrofaunal densities decreased
exponentially with increasing bathymetric depth, but
they also showed substantial seasonal and interannual
differences. In particular, densities were significantly
higher on the upper part of the slope (down to
1500 m) during May than in August and October,
mainly as a result of the presence of large numbers of
juvenile echinoderms including the echinoid Echinus
affinis and the ophiuroid Ophiocten gracilis, both
seasonal breeders. These fluctuations probably reflect
interannular differences in the intensity of phytodetrital
pulses. Polychaetes were always the most important
macrofaunal taxon. Their numbers declined fairly regularly along the transect, and were significantly higher
at the two shallowest stations (208–231 m, 670–693 m)
during May. Crustaceans were most abundant at midslope depths (670–2256 m), significantly more so in
August. Biomass (mg m
−2 ) also tended to decline with
depth, but was consistently higher (1021) at 1034 m
(station B), owing to the predominance of relatively
large animals, and low (1425) at 1457 m (station II)
where the animals were relatively small. Sedimentary
organic carbon peaked at station B, suggesting that this
site received substantial inputs of labile phytodetritus.
Biomass values were somewhat higher in May at the
three shallowest stations (208–1034 m) and higher in
August at mid-slope stations (1425–2256 m), but these
seasonal differences were not significant. Macrofaunal
community respiration rates, estimated from individual
weights and biomass values, were high in May between
208 m and 1034 m, but much lower at the deeper
stations. At mid-slope depths (2200 m), however, rates
were higher in August than in May. Between 40% and
80% of the macrofauna occurred in the 0–1 cm layer of
sediment and the stations of intermediate depth (670 m,
1034 m and 1425 m) showed the highest proportions
within this upper layer.
The numerical density of the megafauna undergoes a steady decrease along the OMEX transect,
but biomass values are more irregular (Duineveld
et al., 1997). Low values are found around the shelf
break (200 m) and upper slope (700 m) (1913 and
1914 g wet weight 1000 m
−2 , respectively) and Pendragon Escarpment (2200 m; 1188 g 1000 m
−2 ), while
the highest values occur at 1450 m (4076 g 1000 m
−2 )
and 3650 m (3789 g 1000 m
−2 ). These irregularities
reflect the changing taxonomic composition of the
megafauna, which is dominated at different depths
by crinoids (200 m), echinoids (700 m), holothurians
(100 m, 3650 m, 4500 m) and poriferans (1450 m).
Among the megafauna, macrofauna and Foraminifera
(>150 mm fraction), the proportion of deposit feeders
generally increased with increasing water depth across