150
Lisa A. LEVIN and Andrew J. GOODAY
densities for individual classes do not exceed 64 individuals m
−2 , except at the Porcupine Abyssal Plain site
where holothurian and ophiuroid densities reach 363
and 965 m
−2 , respectively. Holothurian abundance was
found to correlate well with organic-carbon flux.
Variations in megafaunal composition may have a
temporal as well as a spatial aspect. Results from
the BENGAL Project suggest that a striking and
persistent shift in the composition of the megafauna
occurred on the Porcupine Abyssal Plain during the
1990s (Billett et al., 2002). The holothurian Amperima
rosea exhibited a massive increase in abundance,
and Ellipinion cf molle (holothurian) and Ophiocten
hastatum (ophiuroid) also showed substantial increases
between 1989–1994 and 1996–1999. Billett et al.
(2002) have argued that long-term changes in the
quantity and/or quality of the organic-matter supply to
the seafloor may underlie these fluctuations.
Megafaunal behavior can be addressed by means of
seafloor photography. Examples of this approach being
used in the Atlantic include determination of rates of
movement in echinoderms in the Porcupine Seabight
and Porcupine Abyssal Plain areas (Lampitt and Billett,
1985; Smith et al., 1997b), and feeding activities in
an echiuran on the Cape Verde Abyssal Plain (Bett
and Rice, 1993). In addition, a BATHYSNAP sequence
obtained on the Madeira Abyssal Plain has provided
remarkable documentation of test development in giant
testate protists. The sequence shows three specimens
of the xenophyophore Reticulammina labyrinthica
undergoing a 3–10-fold increase in volume over an
8-month period. Growth occurred episodically and in
distinct phases, each lasting about two days, during
which sediment was collected and incorporated into the
test. The growth phases were separated by periods of
about two months during which the external appearance
of the tests changed little. Gooday et al. (1993) suggested that the xenophyophores used the accumulated
sediment as a source of both food and particles for test
construction, thereby combining growth with deposit
feeding.
Macrofauna: Macrobenthic density and biomass are
also substantially higher on the Porcupine Abyssal
Plain than on the Madeira Abyssal Plain, by factors
of approximately 5 and 35, respectively (Rice, 1993).
Macrofaunal densities on the Cape Verde Abyssal
Plain are very low, only 88 individuals m
−2 of which
59% are polychaetes (Sibuet et al., 1993). Apart
from protobranch bivalves (Allen and Sanders, 1996),
polychaetes are the only macrofaunal group to have
been studied in any detail. Paterson et al. (1994a,b)
compared polychaete populations at sites on three
Northeast Atlantic abyssal plains (Porcupine, Madeira,
Tagus) with those from other regions in the Atlantic
and Pacific Oceans. Polychaetes were more abundant
on the Porcupine Abyssal Plain (302 individuals m
−2 )
than on the Tagus Abyssal Plain (169 individuals
m
−2 ) and Madeira Abyssal Plain (178 individuals
m
−2 ); these densities represented 17%, 27% and 25%,
respectively, of all metazoans >300 mm and 35%,
58% and 49% of the macrofaunal taxa >300 mm.
The Porcupine Abyssal Plain yielded 32 species
and the Tagus Abyssal Plain only 11 species. Several undescribed species of Aphelochaeta, Prionospio
and Sigambra were represented at all three sites.
The five most abundant families on the Porcupine
Abyssal Plain were the Spionidae (25%), Cirratulidae (22%), Sabellidae (10%), Ophelliidae (8%) and
Paraonidae (8%); on the Tagus Abyssal Plain the Cirratulidae (24%), Spionidae (17%), Pilargidae (11%),
Ophelliidae (11%) and Paraonidae (9%); on the
Madeira Abyssal Plain the Sabellidae (24%), Flabelligeridae (20%), Paraonidae (16%), Spionidae (8%)
and Pisionidae (6%). Rarefaction curves indicated that
family richness was higher on the Porcupine Abyssal
Plain and the Tagus Abyssal Plain than on the Madeira
Abyssal Plain.
Meiofauna: Vincx et al. (1994) provides an overview
of meiofauna from the Northeast Atlantic, including the
Porcupine Abyssal Plain, the Madeira Abyssal Plain,
the Cape Verde Abyssal Plain, the Iberian Abyssal Plain
and the BIOTRANS area (Figs. 5.1, 5.2); additional
data on the nematode component are provided by
Vanreusel et al. (1995a) and Lambshead et al. (1995).
Total meiofaunal and nematode densities are higher
at northern abyssal sites (e.g., BIOTRANS, Porcupine
Abyssal Plain; 45–48ºN) than on the Madeira Abyssal
Plain (30ºN) and Cape Verde Abyssal Plain (21ºN); for
example, total densities are almost five times higher
on the Porcupine Abyssal Plain than on the Cape
Verde Abyssal Plain (Vanreusel et al., 1995a). Other
differences are apparent among the nematode fauna.
In particular, there is a substantially higher proportion
of nematodes inhabiting the upper centimeter of
sediment on the Madeira Abyssal Plain compared to the
Porcupine Abyssal Plain (Lambshead et al., 1995), and
mean individual nematode body weight is significantly
lower on the Cape Verde Abyssal Plain compared to
Lisa A. LEVIN and Andrew J. GOODAY
densities for individual classes do not exceed 64 individuals m
−2 , except at the Porcupine Abyssal Plain site
where holothurian and ophiuroid densities reach 363
and 965 m
−2 , respectively. Holothurian abundance was
found to correlate well with organic-carbon flux.
Variations in megafaunal composition may have a
temporal as well as a spatial aspect. Results from
the BENGAL Project suggest that a striking and
persistent shift in the composition of the megafauna
occurred on the Porcupine Abyssal Plain during the
1990s (Billett et al., 2002). The holothurian Amperima
rosea exhibited a massive increase in abundance,
and Ellipinion cf molle (holothurian) and Ophiocten
hastatum (ophiuroid) also showed substantial increases
between 1989–1994 and 1996–1999. Billett et al.
(2002) have argued that long-term changes in the
quantity and/or quality of the organic-matter supply to
the seafloor may underlie these fluctuations.
Megafaunal behavior can be addressed by means of
seafloor photography. Examples of this approach being
used in the Atlantic include determination of rates of
movement in echinoderms in the Porcupine Seabight
and Porcupine Abyssal Plain areas (Lampitt and Billett,
1985; Smith et al., 1997b), and feeding activities in
an echiuran on the Cape Verde Abyssal Plain (Bett
and Rice, 1993). In addition, a BATHYSNAP sequence
obtained on the Madeira Abyssal Plain has provided
remarkable documentation of test development in giant
testate protists. The sequence shows three specimens
of the xenophyophore Reticulammina labyrinthica
undergoing a 3–10-fold increase in volume over an
8-month period. Growth occurred episodically and in
distinct phases, each lasting about two days, during
which sediment was collected and incorporated into the
test. The growth phases were separated by periods of
about two months during which the external appearance
of the tests changed little. Gooday et al. (1993) suggested that the xenophyophores used the accumulated
sediment as a source of both food and particles for test
construction, thereby combining growth with deposit
feeding.
Macrofauna: Macrobenthic density and biomass are
also substantially higher on the Porcupine Abyssal
Plain than on the Madeira Abyssal Plain, by factors
of approximately 5 and 35, respectively (Rice, 1993).
Macrofaunal densities on the Cape Verde Abyssal
Plain are very low, only 88 individuals m
−2 of which
59% are polychaetes (Sibuet et al., 1993). Apart
from protobranch bivalves (Allen and Sanders, 1996),
polychaetes are the only macrofaunal group to have
been studied in any detail. Paterson et al. (1994a,b)
compared polychaete populations at sites on three
Northeast Atlantic abyssal plains (Porcupine, Madeira,
Tagus) with those from other regions in the Atlantic
and Pacific Oceans. Polychaetes were more abundant
on the Porcupine Abyssal Plain (302 individuals m
−2 )
than on the Tagus Abyssal Plain (169 individuals
m
−2 ) and Madeira Abyssal Plain (178 individuals
m
−2 ); these densities represented 17%, 27% and 25%,
respectively, of all metazoans >300 mm and 35%,
58% and 49% of the macrofaunal taxa >300 mm.
The Porcupine Abyssal Plain yielded 32 species
and the Tagus Abyssal Plain only 11 species. Several undescribed species of Aphelochaeta, Prionospio
and Sigambra were represented at all three sites.
The five most abundant families on the Porcupine
Abyssal Plain were the Spionidae (25%), Cirratulidae (22%), Sabellidae (10%), Ophelliidae (8%) and
Paraonidae (8%); on the Tagus Abyssal Plain the Cirratulidae (24%), Spionidae (17%), Pilargidae (11%),
Ophelliidae (11%) and Paraonidae (9%); on the
Madeira Abyssal Plain the Sabellidae (24%), Flabelligeridae (20%), Paraonidae (16%), Spionidae (8%)
and Pisionidae (6%). Rarefaction curves indicated that
family richness was higher on the Porcupine Abyssal
Plain and the Tagus Abyssal Plain than on the Madeira
Abyssal Plain.
Meiofauna: Vincx et al. (1994) provides an overview
of meiofauna from the Northeast Atlantic, including the
Porcupine Abyssal Plain, the Madeira Abyssal Plain,
the Cape Verde Abyssal Plain, the Iberian Abyssal Plain
and the BIOTRANS area (Figs. 5.1, 5.2); additional
data on the nematode component are provided by
Vanreusel et al. (1995a) and Lambshead et al. (1995).
Total meiofaunal and nematode densities are higher
at northern abyssal sites (e.g., BIOTRANS, Porcupine
Abyssal Plain; 45–48ºN) than on the Madeira Abyssal
Plain (30ºN) and Cape Verde Abyssal Plain (21ºN); for
example, total densities are almost five times higher
on the Porcupine Abyssal Plain than on the Cape
Verde Abyssal Plain (Vanreusel et al., 1995a). Other
differences are apparent among the nematode fauna.
In particular, there is a substantially higher proportion
of nematodes inhabiting the upper centimeter of
sediment on the Madeira Abyssal Plain compared to the
Porcupine Abyssal Plain (Lambshead et al., 1995), and
mean individual nematode body weight is significantly
lower on the Cape Verde Abyssal Plain compared to