THE DEEP ATLANTIC OCEAN
141
Porcupine Seabight (Rice et al., 1990), local densities
off Morocco may reach up to 6 individuals m
−2
in single photographs. Of particular interest was the
distribution of live and dead sponges, which suggested
a progressive upslope movement of the population,
possibly in search of a richer food supply.
Gal´ eron et al. (2000), observed that total metazoan density and biomass (megafauna, macrofauna,
and meiofauna) decreased with increasing depth and
decreasing food supply across the EUMELI stations.
However, each faunal component studied responded
differently to the variation in food input. Overall,
the megafauna dominated biomass at the most eutrophic site, macrofauna dominated at intermediate
food conditions, and meiofauna dominated at the
most oligotrophic site. However, within metazoan
size groups, some taxa (e.g., sponges, tunicates and
holothuroids) did not follow this pattern, implying that
food availability is not the sole control on community
structure.
A close relation between benthic foraminiferal
biomass and surface primary production exists along
the Northwest African margin (Altenbach, 1988; Altenbach and Sarnthein, 1989). The species composition
of foraminiferal assemblages is also controlled, at least
partly, by organic-matter fluxes (Lutze, 1980; Lutze and
Coulbourne, 1984). In particular, a Uvigerina peregrina
biofacies predominates in areas to the south of 22ºN
(near Cap Blanc) where the annual flux rate exceeds
2–3 g C m
−2 , whereas a Cibicidoides wuellerstorfi/C.
kullenbergi biofacies occupies lower-productivity areas
to the north (Lutze and Coulbourne, 1984; Altenbach,
1988). Other factors influencing foraminiferal faunas
along this margin include bathymetry, sediment granulometry and bottom-water oxygen concentrations.
Northeast Atlantic abyssal plains
The faunas of Northeast Atlantic abyssal plains are
known in varying degrees of detail as a result of
recent national and international sampling programs
(Table 5.1). The Porcupine Abyssal Plain has been
particularly well studied within the framework of
BENGAL and earlier projects funded by the European
Union. Many of the biological and geochemical results
of the BENGAL Project have appeared in a recent
special volume (Billett, 2002).
Megafauna: Thurston et al. (1994) have provided
a detailed account of the megafauna (>4 mm) of
the Porcupine Abyssal Plain, Madeira Abyssal Plain
(MAP) and Great Meteor East region (GME) and have
summarized comparable published data (derived from
net catches and in situ photographs) from other abyssal
plains (Table 5.3). One of the most striking conclusions
of this analysis is that megafaunal biomass is much
greater (16–39×) at 48ºN on the Porcupine Abyssal
Plain than it is in the Madeira Abyssal Plain and the
Great Meteor East region areas (both at 31ºN); there is
a corresponding but much smaller disparity in density
values. The biomass differences are mirrored in the
taxonomic composition of the megafauna in regions
to the north of 40ºN and south of 33ºN. Holothurians,
actiniarians, and to a lesser extent asteroids, constitute a
major proportion of the invertebrate megafauna, both in
terms of abundance and (particularly for holothurians)
biomass, on the Porcupine Abyssal Plain (Thurston
et al., 1994) and Iberian Abyssal Plains (Feldt et al.,
1989). On the Madeira Abyssal Plain and in the
Great Meteor East area (i.e. to the south of 33ºN)
the megafauna is dominated by asteroids and natant
decapods, with holothurians constituting a relatively
small proportion of the fauna. Similarly, the Cape Verde
Abyssal Plain (CVAP) harbors a sparse megafauna
(0.00052 individuals m
−2 ) (Bett et al., 1995). One
may note that values for megafaunal density from
the Cape Verde Abyssal Plain given by Sibuet et al.
(1993), which are an order of magnitude greater
than those of Bett et al. (1995), are based on the
>1mm fraction and therefore include animals normally
considered as macrofauna. Thurston et al. (1994)
have suggested that the large holothurian-dominated
biomass on the Porcupine Abyssal Plain is supported
by the phytodetritus flux which occurs in this area but
not to the south of 33ºN.
Sibuet (1985) has presented a survey of the echinoderm fauna of deep Atlantic basins, mainly abyssal
plains but including some continental-margin regions.
Echinoderms constitute a highly variable proportion
of the total megafauna in samples from >4000 m:
12% (Angola Basin, 5250 m), 33% (Cape Basin,
4650 m), 63% (Demerara Plain near the Amazon cone,
4420 m), 19% (Demerara Plain, 4850 m), 20% (Vema
fracture zone, 5100 m), 3% (Cape Verde Abyssal
Plain, 5190 m), 48% (southern Bay of Biscay, 4450 m),
20% (northern Bay of Biscay, 4750 m), 17% (northern
Bay of Biscay, 4200 m), 75% (Porcupine Abyssal
Plain, 4820 m). The dominant classes are always either
holothurians (Angola Basin, Demerara Abyssal Plain,
Vema fracture zone, Cape Verde Abyssal Plain, northern Bay of Biscay) or ophiuroids (Cape Basin, southern
Bay of Biscay, Porcupine Abyssal Plain). Maximum
141
Porcupine Seabight (Rice et al., 1990), local densities
off Morocco may reach up to 6 individuals m
−2
in single photographs. Of particular interest was the
distribution of live and dead sponges, which suggested
a progressive upslope movement of the population,
possibly in search of a richer food supply.
Gal´ eron et al. (2000), observed that total metazoan density and biomass (megafauna, macrofauna,
and meiofauna) decreased with increasing depth and
decreasing food supply across the EUMELI stations.
However, each faunal component studied responded
differently to the variation in food input. Overall,
the megafauna dominated biomass at the most eutrophic site, macrofauna dominated at intermediate
food conditions, and meiofauna dominated at the
most oligotrophic site. However, within metazoan
size groups, some taxa (e.g., sponges, tunicates and
holothuroids) did not follow this pattern, implying that
food availability is not the sole control on community
structure.
A close relation between benthic foraminiferal
biomass and surface primary production exists along
the Northwest African margin (Altenbach, 1988; Altenbach and Sarnthein, 1989). The species composition
of foraminiferal assemblages is also controlled, at least
partly, by organic-matter fluxes (Lutze, 1980; Lutze and
Coulbourne, 1984). In particular, a Uvigerina peregrina
biofacies predominates in areas to the south of 22ºN
(near Cap Blanc) where the annual flux rate exceeds
2–3 g C m
−2 , whereas a Cibicidoides wuellerstorfi/C.
kullenbergi biofacies occupies lower-productivity areas
to the north (Lutze and Coulbourne, 1984; Altenbach,
1988). Other factors influencing foraminiferal faunas
along this margin include bathymetry, sediment granulometry and bottom-water oxygen concentrations.
Northeast Atlantic abyssal plains
The faunas of Northeast Atlantic abyssal plains are
known in varying degrees of detail as a result of
recent national and international sampling programs
(Table 5.1). The Porcupine Abyssal Plain has been
particularly well studied within the framework of
BENGAL and earlier projects funded by the European
Union. Many of the biological and geochemical results
of the BENGAL Project have appeared in a recent
special volume (Billett, 2002).
Megafauna: Thurston et al. (1994) have provided
a detailed account of the megafauna (>4 mm) of
the Porcupine Abyssal Plain, Madeira Abyssal Plain
(MAP) and Great Meteor East region (GME) and have
summarized comparable published data (derived from
net catches and in situ photographs) from other abyssal
plains (Table 5.3). One of the most striking conclusions
of this analysis is that megafaunal biomass is much
greater (16–39×) at 48ºN on the Porcupine Abyssal
Plain than it is in the Madeira Abyssal Plain and the
Great Meteor East region areas (both at 31ºN); there is
a corresponding but much smaller disparity in density
values. The biomass differences are mirrored in the
taxonomic composition of the megafauna in regions
to the north of 40ºN and south of 33ºN. Holothurians,
actiniarians, and to a lesser extent asteroids, constitute a
major proportion of the invertebrate megafauna, both in
terms of abundance and (particularly for holothurians)
biomass, on the Porcupine Abyssal Plain (Thurston
et al., 1994) and Iberian Abyssal Plains (Feldt et al.,
1989). On the Madeira Abyssal Plain and in the
Great Meteor East area (i.e. to the south of 33ºN)
the megafauna is dominated by asteroids and natant
decapods, with holothurians constituting a relatively
small proportion of the fauna. Similarly, the Cape Verde
Abyssal Plain (CVAP) harbors a sparse megafauna
(0.00052 individuals m
−2 ) (Bett et al., 1995). One
may note that values for megafaunal density from
the Cape Verde Abyssal Plain given by Sibuet et al.
(1993), which are an order of magnitude greater
than those of Bett et al. (1995), are based on the
>1mm fraction and therefore include animals normally
considered as macrofauna. Thurston et al. (1994)
have suggested that the large holothurian-dominated
biomass on the Porcupine Abyssal Plain is supported
by the phytodetritus flux which occurs in this area but
not to the south of 33ºN.
Sibuet (1985) has presented a survey of the echinoderm fauna of deep Atlantic basins, mainly abyssal
plains but including some continental-margin regions.
Echinoderms constitute a highly variable proportion
of the total megafauna in samples from >4000 m:
12% (Angola Basin, 5250 m), 33% (Cape Basin,
4650 m), 63% (Demerara Plain near the Amazon cone,
4420 m), 19% (Demerara Plain, 4850 m), 20% (Vema
fracture zone, 5100 m), 3% (Cape Verde Abyssal
Plain, 5190 m), 48% (southern Bay of Biscay, 4450 m),
20% (northern Bay of Biscay, 4750 m), 17% (northern
Bay of Biscay, 4200 m), 75% (Porcupine Abyssal
Plain, 4820 m). The dominant classes are always either
holothurians (Angola Basin, Demerara Abyssal Plain,
Vema fracture zone, Cape Verde Abyssal Plain, northern Bay of Biscay) or ophiuroids (Cape Basin, southern
Bay of Biscay, Porcupine Abyssal Plain). Maximum