210
Craig R. SMITH and Amanda W.J. DEMOPOULOS
and Baldwin, 1984; K.L. Smith, 1989). However,
because of insufficient temporal coverage from sediment traps and seafloor respirometers, the strength of
coupling between surface-ocean processes and seafloor
respiration in the oligotrophic abyss remains unclear.
Seamounts
There are tens of thousands of seamounts protruding
more than one thousand meters above the abyssal
seafloor of the Pacific; these create a complex mosaic
of deep-sea benthic habitats.
Habitat and community description
Many Pacific seamounts are steep-sided and currentswept because of intensification of topographic flow;
these contain large areas of rocky substratum. Many
seamounts also contain soft sediments (frequently
foraminiferal or basaltic sands) inside craters and on
level benches and shelves where slopes and currents
are moderate enough to allow sediment accumulation
[see Levin et al. (1991c) for a schematic diagram of
a typical seamount]. Seamounts interact with ocean
currents on a variety of scales, potentially yielding internal waves, eddy formation, local upwelling
and trapped circulation cells called Taylor columns
(Boehlert and Genin, 1987). Because of the complex
nature of seamount topography, current regimes and
sediment composition, benthic habitats on seamounts
typically are highly heterogeneous on scales of 1–10 km
(Boehlert and Genin, 1987; Levin et al., 1991c, 1994),
making broad ecological generalizations difficult.
The benthic ecology of Pacific seamounts has
received significant study because these features may
support productive (albeit small-scale) fisheries
(Boehlert and Genin, 1987; Rogers, 1994), they may
be of strategic significance for submarine warfare,
and they may provide sites for allopatric speciation
in populations with restricted bathymetric distributions
(Wilson and Kaufmann, 1987).
The hard, rocky substratum of deep seamounts is
characterized by suspension-feeding megabenthos such
as antipatharians, gorgonians and other cnidarians, as
well as occasional crinoids, ophiuroids, cirripeds and a
variety of other taxa (Genin et al., 1986; Wilson and
Kaufmann, 1987; Grigg et al., 1987; Rogers, 1994).
Suspension-feeding antipatharians and gorgonians typically are more abundant near seamount peaks, where
flow acceleration may enhance the flux of suspended
food particles (Genin et al., 1986); these same taxa
are much less abundant where currents are reduced,
or where manganese crusts may inhibit recruitment
(Grigg et al., 1987). A number of precious corals are
found on Pacific seamounts and some are commercially harvested. These include red and pink corals
(Corallium spp.) and black corals (Antipathes spp.)
(Rogers, 1994). A surprisingly large proportion of
the world’s catch of red coral historically has come
from Pacific seamounts; for example, in 1983, roughly
140 000 kg (70% of the world catch) of red coral
was harvested from the Emperor–Hawaiian seamounts
(Rogers, 1994). These deep corals are characterized by
very low rates of recruitment and growth, and may
easily be overexploited (Grigg, 1984).
Large xenophyophores dominate the megafauna on
soft substrata of many bathyal seamounts in the eastern
Pacific, reaching densities as high as 18 m
−2 (Levin
and Thomas, 1988). The decimeter-sized tests of
xenophyophores provide habitat for a broad range of
macrofaunal and meiofaunal taxa, including isopods,
tanaids, ophiuroids and nematodes, contributing to
small-scale spatial heterogeneity of seamount sediment communities. Xenophyophores are thus likely to
contribute to the maintenance of species diversity in
seamount sediments (Levin and Thomas, 1988).
The infauna of a variety of deep Pacific seamounts
has been studied to explore the effects of hydrodynamic
regime, sediment type and mobility, water depth and
latitude on macrobenthic community structure and
recolonization rates. In a study of 18 seamounts ranging
in depth from 788 to 3533 m, Levin et al. (1991c)
found little relationship between the abundance of
polychaetes and either water depth or sediment sand
content. In addition, the representation of polychaete
families on the seamounts was similar to that in
other deep-sea soft-substratum communities, and levels
of species diversity were comparable. However, filter
feeders, especially sabellids, were more abundant in
rippled foraminiferal sands that in other sediment types
(Levin et al., 1991c). At water depths of 1480 to
3150 m on Horizon Guyot and Magellan Rise in the
central Pacific, Levin and Thomas (1989) found substantial differences between macrobenthos in coarse,
rippled sands (subjected to strong bottom corrents)
and assemblages in unrippled, finer-grained sediments.
Macrobenthos were less abundant in the high energy
sites (255 m
−2 versus 388 to 829 m
−2 ), and were dominated by sessile, surface-feeding forms. In contrast,
the quieter, finer-grained sediments were dominated by
motile, subsurface-feeding forms living closer to the
Craig R. SMITH and Amanda W.J. DEMOPOULOS
and Baldwin, 1984; K.L. Smith, 1989). However,
because of insufficient temporal coverage from sediment traps and seafloor respirometers, the strength of
coupling between surface-ocean processes and seafloor
respiration in the oligotrophic abyss remains unclear.
Seamounts
There are tens of thousands of seamounts protruding
more than one thousand meters above the abyssal
seafloor of the Pacific; these create a complex mosaic
of deep-sea benthic habitats.
Habitat and community description
Many Pacific seamounts are steep-sided and currentswept because of intensification of topographic flow;
these contain large areas of rocky substratum. Many
seamounts also contain soft sediments (frequently
foraminiferal or basaltic sands) inside craters and on
level benches and shelves where slopes and currents
are moderate enough to allow sediment accumulation
[see Levin et al. (1991c) for a schematic diagram of
a typical seamount]. Seamounts interact with ocean
currents on a variety of scales, potentially yielding internal waves, eddy formation, local upwelling
and trapped circulation cells called Taylor columns
(Boehlert and Genin, 1987). Because of the complex
nature of seamount topography, current regimes and
sediment composition, benthic habitats on seamounts
typically are highly heterogeneous on scales of 1–10 km
(Boehlert and Genin, 1987; Levin et al., 1991c, 1994),
making broad ecological generalizations difficult.
The benthic ecology of Pacific seamounts has
received significant study because these features may
support productive (albeit small-scale) fisheries
(Boehlert and Genin, 1987; Rogers, 1994), they may
be of strategic significance for submarine warfare,
and they may provide sites for allopatric speciation
in populations with restricted bathymetric distributions
(Wilson and Kaufmann, 1987).
The hard, rocky substratum of deep seamounts is
characterized by suspension-feeding megabenthos such
as antipatharians, gorgonians and other cnidarians, as
well as occasional crinoids, ophiuroids, cirripeds and a
variety of other taxa (Genin et al., 1986; Wilson and
Kaufmann, 1987; Grigg et al., 1987; Rogers, 1994).
Suspension-feeding antipatharians and gorgonians typically are more abundant near seamount peaks, where
flow acceleration may enhance the flux of suspended
food particles (Genin et al., 1986); these same taxa
are much less abundant where currents are reduced,
or where manganese crusts may inhibit recruitment
(Grigg et al., 1987). A number of precious corals are
found on Pacific seamounts and some are commercially harvested. These include red and pink corals
(Corallium spp.) and black corals (Antipathes spp.)
(Rogers, 1994). A surprisingly large proportion of
the world’s catch of red coral historically has come
from Pacific seamounts; for example, in 1983, roughly
140 000 kg (70% of the world catch) of red coral
was harvested from the Emperor–Hawaiian seamounts
(Rogers, 1994). These deep corals are characterized by
very low rates of recruitment and growth, and may
easily be overexploited (Grigg, 1984).
Large xenophyophores dominate the megafauna on
soft substrata of many bathyal seamounts in the eastern
Pacific, reaching densities as high as 18 m
−2 (Levin
and Thomas, 1988). The decimeter-sized tests of
xenophyophores provide habitat for a broad range of
macrofaunal and meiofaunal taxa, including isopods,
tanaids, ophiuroids and nematodes, contributing to
small-scale spatial heterogeneity of seamount sediment communities. Xenophyophores are thus likely to
contribute to the maintenance of species diversity in
seamount sediments (Levin and Thomas, 1988).
The infauna of a variety of deep Pacific seamounts
has been studied to explore the effects of hydrodynamic
regime, sediment type and mobility, water depth and
latitude on macrobenthic community structure and
recolonization rates. In a study of 18 seamounts ranging
in depth from 788 to 3533 m, Levin et al. (1991c)
found little relationship between the abundance of
polychaetes and either water depth or sediment sand
content. In addition, the representation of polychaete
families on the seamounts was similar to that in
other deep-sea soft-substratum communities, and levels
of species diversity were comparable. However, filter
feeders, especially sabellids, were more abundant in
rippled foraminiferal sands that in other sediment types
(Levin et al., 1991c). At water depths of 1480 to
3150 m on Horizon Guyot and Magellan Rise in the
central Pacific, Levin and Thomas (1989) found substantial differences between macrobenthos in coarse,
rippled sands (subjected to strong bottom corrents)
and assemblages in unrippled, finer-grained sediments.
Macrobenthos were less abundant in the high energy
sites (255 m
−2 versus 388 to 829 m
−2 ), and were dominated by sessile, surface-feeding forms. In contrast,
the quieter, finer-grained sediments were dominated by
motile, subsurface-feeding forms living closer to the