THE DEEP ATLANTIC OCEAN
151
the Porcupine Abyssal Plain, mainly due to the greater
abundance of large nematodes at the more northerly site
(Vanreusel et al., 1995a). These contrasts are believed
to reflect differences in the supply of organic matter
to the seafloor, in particular the fact that the deposition
of aggregated phytodetritus is restricted to the northern
part of the Northeast Atlantic (Porcupine Abyssal Plain
and BIOTRANS area).
Gooday (1996b) has given a detailed analysis at the
species level of foraminiferal assemblages in multiplecorer samples (top 1 cm of sediment) collected from
the Porcupine Abyssal Plain, Madeira Abyssal Plain
and Cape Verde Abyssal Plain during August, 1989.
Foraminifera accounted for 61–76% of the total meiofauna in these samples. Densities were higher on the
Porcupine Abyssal Plain than at the two southern sites,
and part of the difference is accounted for by specimens
inhabiting the phytodetrital layer, present only at
on the Porcupine Abyssal Plain. The phytodetrital
foraminiferal populations were of low diversity and
dominated by a few apparently opportunistic species
(e.g., Epistominella exigua). These species are typically
much less common in the underlying sediment, so
that the phytodetrital assemblages can be regarded
as being to some extent ‘decoupled’ from those in
the underlying sediment. Total populations, from the
phytodetritus plus the 0–1 cm sediment layer, are
highly diverse (123–167 species) and broadly similar
in their species composition. However, in addition to
the phytodetritus-exploiting species, some sedimentdwelling species of ‘Hyperammina’, Lagenammina,
Leptohalysis and Reophax were more abundant at the
Porcupine Abyssal Plain site whereas a few, such as
Lagenammina tubulata and Subreophax aduncus, were
more abundant at the southern sites.
Northeast Atlantic Seamounts
Seamounts are abundant in the deep Atlantic (Epp
and Smoot, 1989), but there have been few ecological descriptions of their benthic communities
(Rogers, 1994). The best studied are the Meteor
and Vema Seamounts, but even here the papers are
few, and mostly are taxonomic in nature (citations
within Rogers, 1994). Thiel (1970, 1975) studied
the meiofaunal communities of the Great Meteor
Seamount, 1600 km from the coast of Africa, and
the Josephine Seamount, 300 miles west of southern
Portugal in a region of higher primary productivity.
Samples taken from the summit plateaus at depths
of 206–355 m and 292–350 m yielded mean densities
of 40.3±14.0 individuals cm
−2 and 22.7±7.4 individuals cm
−2 on Josephine and Meteor, respectively.
Samples taken by Rachor (1975) just southwest of the
Josephine Seamount were much lower. The Meteor
data suggest little difference in meiofauna between
the shallow seamount and the Iberian Abyssal Plain
5000 m deeper, although primary productivity may be
twice as much above the Iberian deep sea. Heavy
predation pressure by fishes and strong currents above
the Great Meteor Seamount may have reduced meiofaunal densities (Thiel, 1975). In the South Atlantic,
Russian investigations have contributed to knowledge
of the seamount faunas, for example, on the Valdivia
Seamount (Kamenskaya, 1988).
North Atlantic necrophages
Necrophages (animals which scavenge dead carcasses)
play an important role in the cycling of organic
matter on the deep-sea floor (Haedrich and Rowe,
1977; Smith, 1985a). Megafaunal necrophages usually
congregate around large carcasses within hours of
the carcass reaching the seabed, and are capable of
consuming all but the bones within days (Hargrave,
1985). Among the commonest necrophages in the deep
Atlantic are fish (particularly macrourids, ophidioids
and synaphobranchiid eels), natantian decapods, and
amphipods (almost entirely lysianassids). These highly
mobile benthopelagic animals appear to be concentrated within, at most, a few meters of the deep-sea
floor, but can swim up hundreds or even thousands
of meters into the overlying water column (Smith
et al., 1979; Thurston, 1990; Sainte-Marie, 1992). In
particular, the amphipod Eurythenes gryllus undergoes
an ontogenetic migration hundreds of meters up into
the water column (Charmasson and Calmet, 1987;
Christiansen et al., 1990; Christiansen, 1996). It is
notable that dominant scavengers in the Pacific, such
as hagfish, sablefish and ophiuroids (Smith, 1985a), are
not observed at bait in the deep Atlantic.
The existence of necrophages in the deep sea was
first revealed in the Northeast Atlantic when amphipods
were caught in baited traps deployed from the Prince
of Monaco’s yacht L’Hirondelle during its campaign
of 1888 (Chevreux, 1900; Richard, 1934). Baited traps
are the most effective means of sampling scavenging
amphipods (Thurston, 1979; Hargrave, 1985; Hargrave
et al., 1995), whereas larger animals such as fish and
decapods are best documented by means of baited
cameras (Isaacs, 1969). Both fish and amphipods
151
the Porcupine Abyssal Plain, mainly due to the greater
abundance of large nematodes at the more northerly site
(Vanreusel et al., 1995a). These contrasts are believed
to reflect differences in the supply of organic matter
to the seafloor, in particular the fact that the deposition
of aggregated phytodetritus is restricted to the northern
part of the Northeast Atlantic (Porcupine Abyssal Plain
and BIOTRANS area).
Gooday (1996b) has given a detailed analysis at the
species level of foraminiferal assemblages in multiplecorer samples (top 1 cm of sediment) collected from
the Porcupine Abyssal Plain, Madeira Abyssal Plain
and Cape Verde Abyssal Plain during August, 1989.
Foraminifera accounted for 61–76% of the total meiofauna in these samples. Densities were higher on the
Porcupine Abyssal Plain than at the two southern sites,
and part of the difference is accounted for by specimens
inhabiting the phytodetrital layer, present only at
on the Porcupine Abyssal Plain. The phytodetrital
foraminiferal populations were of low diversity and
dominated by a few apparently opportunistic species
(e.g., Epistominella exigua). These species are typically
much less common in the underlying sediment, so
that the phytodetrital assemblages can be regarded
as being to some extent ‘decoupled’ from those in
the underlying sediment. Total populations, from the
phytodetritus plus the 0–1 cm sediment layer, are
highly diverse (123–167 species) and broadly similar
in their species composition. However, in addition to
the phytodetritus-exploiting species, some sedimentdwelling species of ‘Hyperammina’, Lagenammina,
Leptohalysis and Reophax were more abundant at the
Porcupine Abyssal Plain site whereas a few, such as
Lagenammina tubulata and Subreophax aduncus, were
more abundant at the southern sites.
Northeast Atlantic Seamounts
Seamounts are abundant in the deep Atlantic (Epp
and Smoot, 1989), but there have been few ecological descriptions of their benthic communities
(Rogers, 1994). The best studied are the Meteor
and Vema Seamounts, but even here the papers are
few, and mostly are taxonomic in nature (citations
within Rogers, 1994). Thiel (1970, 1975) studied
the meiofaunal communities of the Great Meteor
Seamount, 1600 km from the coast of Africa, and
the Josephine Seamount, 300 miles west of southern
Portugal in a region of higher primary productivity.
Samples taken from the summit plateaus at depths
of 206–355 m and 292–350 m yielded mean densities
of 40.3±14.0 individuals cm
−2 and 22.7±7.4 individuals cm
−2 on Josephine and Meteor, respectively.
Samples taken by Rachor (1975) just southwest of the
Josephine Seamount were much lower. The Meteor
data suggest little difference in meiofauna between
the shallow seamount and the Iberian Abyssal Plain
5000 m deeper, although primary productivity may be
twice as much above the Iberian deep sea. Heavy
predation pressure by fishes and strong currents above
the Great Meteor Seamount may have reduced meiofaunal densities (Thiel, 1975). In the South Atlantic,
Russian investigations have contributed to knowledge
of the seamount faunas, for example, on the Valdivia
Seamount (Kamenskaya, 1988).
North Atlantic necrophages
Necrophages (animals which scavenge dead carcasses)
play an important role in the cycling of organic
matter on the deep-sea floor (Haedrich and Rowe,
1977; Smith, 1985a). Megafaunal necrophages usually
congregate around large carcasses within hours of
the carcass reaching the seabed, and are capable of
consuming all but the bones within days (Hargrave,
1985). Among the commonest necrophages in the deep
Atlantic are fish (particularly macrourids, ophidioids
and synaphobranchiid eels), natantian decapods, and
amphipods (almost entirely lysianassids). These highly
mobile benthopelagic animals appear to be concentrated within, at most, a few meters of the deep-sea
floor, but can swim up hundreds or even thousands
of meters into the overlying water column (Smith
et al., 1979; Thurston, 1990; Sainte-Marie, 1992). In
particular, the amphipod Eurythenes gryllus undergoes
an ontogenetic migration hundreds of meters up into
the water column (Charmasson and Calmet, 1987;
Christiansen et al., 1990; Christiansen, 1996). It is
notable that dominant scavengers in the Pacific, such
as hagfish, sablefish and ophiuroids (Smith, 1985a), are
not observed at bait in the deep Atlantic.
The existence of necrophages in the deep sea was
first revealed in the Northeast Atlantic when amphipods
were caught in baited traps deployed from the Prince
of Monaco’s yacht L’Hirondelle during its campaign
of 1888 (Chevreux, 1900; Richard, 1934). Baited traps
are the most effective means of sampling scavenging
amphipods (Thurston, 1979; Hargrave, 1985; Hargrave
et al., 1995), whereas larger animals such as fish and
decapods are best documented by means of baited
cameras (Isaacs, 1969). Both fish and amphipods