THE DEEP PACIFIC OCEAN FLOOR
193
are carrion falls. For example, Smith (1983) found
that 0.2 kg parcels of the giant kelp Macrocystis
pyrifera were consumed in the Santa Catalina Basin
by the gastropod Bathybembix bairdii, the ophiuroid
Ophiophthalmus normani, and the shrimp Pandalopsis
ampla over a period of roughly 24 days, with little
feeding occurring until the kelp had aged for 1–
2 weeks. The requirement for aging, and presumably
microbial colonization, of M. pyrifera likely reflects the
much lower content of labile protein in kelp relative
to carrion (Smith, 1983). The rates and patterns of
consumption of anthropogenic materials introduced to
slope habitats (e.g., trawl by-catch, sewage sludge,
and municipal garbage) also varies with the quality
of organic matter contained within these materials.
The rapid consumption of whale carcasses does not
necessarily indicate that tons of anthropogenic waste
deposited at a point on the seafloor will be dispersed
and assimilated by slope communities on time scales
of months.
While scavenging may be the most dramatic trophic
mode for metazoa on the sediment-covered California
slope, deposit feeding (i.e., the ingestion of sediment
grains and associated organic matter) may be the most
prevalent. For example, more than 90% of metazoan
macrofaunal individuals in Santa Catalina Basin (Kukert and Smith, 1992; C.R. Smith et al., 1998) and more
than 90% of the polychaetes (the dominant macrofaunal group) in the San Diego Trough can be classified
as deposit feeders (Jumars and Gallagher, 1982). In the
San Diego Trough, the polychaetes are split roughly
equally between species feeding within the sediment
column (subsurface deposit feeders) and those consuming particles at the sediment surface (surface deposit
feeders), while in the Santa Catalina Basin, subsurface
deposit feeders dominate the macrofauna. The predominance of subsurface deposit feeders in the Santa
Catalina Basin may be related to the high organiccarbon content of sediments in this basin [5 to 7% organic carbon by weight versus 1.2 to 4% in most other
California slope and basin muds (Emery, 1960; K.L.
Smith et al., 1983; Reimers et al., 1992)] which may
lead to relatively high concentrations of labile organic
matter and bacterial biomass within the sediments.
The most abundant California slope megafauna
also tend to be deposit feeders. Mobile epibenthic holothuroids such as Pannychia moseleyi and
Scotoplanes globosa in Santa Catalina Basin, and
Abyssocucumis abyssorum and Oneirophanta mutabilis at 4100 m off central California, wander over
the seafloor consuming a thin veneer of superficial
sediment particles. Studies with naturally occurring
radiotracers (
234 Th) and labile phytoplankton pigments
(chlorophyll a) indicate that these holothurians are extremely selective, ingesting small sedimenting particles
and/or phytodetrital aggregates that have reached the
seafloor in the previous 30 days (Lauerman et al., 1997;
Miller et al., 2000). Such freshly deposited particles are
likely to have a relatively high food value, because any
labile organic material they have carried from surface
waters will be little degraded by seafloor bacteria
(C.R. Smith et al., 1993). Other common megafaunal
surface-deposit feeders on the California slope include
large gastropods such as Bathybembix bairdii and
the burrowing chiridotid holothurian Chirodota sp.
(Miller et al., 2000). These species also consume
recently deposited particles on the seafloor, but are
substantially less selective than the four epifaunal
holothurians mentioned above, consuming sediments
that are on average 60–120 days old (Miller et al.,
2000). Differences in particle selectivity may result
from differences in mechanisms of particle pickup,
different mobility (relatively slow burrowers may lose
the race to particulate organic carbonkets of young
particles), or variations in digestive strategies (Penry
and Jumars, 1987; Miller et al., 2000). The megafaunal
populations can feed at surprisingly high rates, potentially ingesting ~30% of the daily flux of particulate
organic carbon to the seafloor in the Santa Catalina
Basin (Miller et al., 2000). Thus, the oft-overlooked
megabenthos may play an important role in modifying
and redistributing the limited flux of particulate organic
carbon reaching slope communities.
Based largely on inferences from studies in other
regions, detritivory (which includes scavenging, deposit
feeding, and uptake of dissolved organic matter) predominates within the meiofauna of the California slope.
For example, deep-sea Foraminifera, as a group, consume phytodetritus and the remains of small animals,
sediment grains with associated bacteria and particulate
organic carbon, and, possibly, dissolved organic matter
(Gooday et al., 1992). The nematodes and harpacticoids
similarly appear to feed predominantly on detrital
particles, sediment and/or bacteria (e.g., Gage and
Tyler, 1991; J. Lambshead, personal communication),
although some are certainly predatory. Thus, a very
slim data base suggests that the California slope
meiofauna predominantly occupy low trophic levels.
In general, specialized predators appear to constitute
193
are carrion falls. For example, Smith (1983) found
that 0.2 kg parcels of the giant kelp Macrocystis
pyrifera were consumed in the Santa Catalina Basin
by the gastropod Bathybembix bairdii, the ophiuroid
Ophiophthalmus normani, and the shrimp Pandalopsis
ampla over a period of roughly 24 days, with little
feeding occurring until the kelp had aged for 1–
2 weeks. The requirement for aging, and presumably
microbial colonization, of M. pyrifera likely reflects the
much lower content of labile protein in kelp relative
to carrion (Smith, 1983). The rates and patterns of
consumption of anthropogenic materials introduced to
slope habitats (e.g., trawl by-catch, sewage sludge,
and municipal garbage) also varies with the quality
of organic matter contained within these materials.
The rapid consumption of whale carcasses does not
necessarily indicate that tons of anthropogenic waste
deposited at a point on the seafloor will be dispersed
and assimilated by slope communities on time scales
of months.
While scavenging may be the most dramatic trophic
mode for metazoa on the sediment-covered California
slope, deposit feeding (i.e., the ingestion of sediment
grains and associated organic matter) may be the most
prevalent. For example, more than 90% of metazoan
macrofaunal individuals in Santa Catalina Basin (Kukert and Smith, 1992; C.R. Smith et al., 1998) and more
than 90% of the polychaetes (the dominant macrofaunal group) in the San Diego Trough can be classified
as deposit feeders (Jumars and Gallagher, 1982). In the
San Diego Trough, the polychaetes are split roughly
equally between species feeding within the sediment
column (subsurface deposit feeders) and those consuming particles at the sediment surface (surface deposit
feeders), while in the Santa Catalina Basin, subsurface
deposit feeders dominate the macrofauna. The predominance of subsurface deposit feeders in the Santa
Catalina Basin may be related to the high organiccarbon content of sediments in this basin [5 to 7% organic carbon by weight versus 1.2 to 4% in most other
California slope and basin muds (Emery, 1960; K.L.
Smith et al., 1983; Reimers et al., 1992)] which may
lead to relatively high concentrations of labile organic
matter and bacterial biomass within the sediments.
The most abundant California slope megafauna
also tend to be deposit feeders. Mobile epibenthic holothuroids such as Pannychia moseleyi and
Scotoplanes globosa in Santa Catalina Basin, and
Abyssocucumis abyssorum and Oneirophanta mutabilis at 4100 m off central California, wander over
the seafloor consuming a thin veneer of superficial
sediment particles. Studies with naturally occurring
radiotracers (
234 Th) and labile phytoplankton pigments
(chlorophyll a) indicate that these holothurians are extremely selective, ingesting small sedimenting particles
and/or phytodetrital aggregates that have reached the
seafloor in the previous 30 days (Lauerman et al., 1997;
Miller et al., 2000). Such freshly deposited particles are
likely to have a relatively high food value, because any
labile organic material they have carried from surface
waters will be little degraded by seafloor bacteria
(C.R. Smith et al., 1993). Other common megafaunal
surface-deposit feeders on the California slope include
large gastropods such as Bathybembix bairdii and
the burrowing chiridotid holothurian Chirodota sp.
(Miller et al., 2000). These species also consume
recently deposited particles on the seafloor, but are
substantially less selective than the four epifaunal
holothurians mentioned above, consuming sediments
that are on average 60–120 days old (Miller et al.,
2000). Differences in particle selectivity may result
from differences in mechanisms of particle pickup,
different mobility (relatively slow burrowers may lose
the race to particulate organic carbonkets of young
particles), or variations in digestive strategies (Penry
and Jumars, 1987; Miller et al., 2000). The megafaunal
populations can feed at surprisingly high rates, potentially ingesting ~30% of the daily flux of particulate
organic carbon to the seafloor in the Santa Catalina
Basin (Miller et al., 2000). Thus, the oft-overlooked
megabenthos may play an important role in modifying
and redistributing the limited flux of particulate organic
carbon reaching slope communities.
Based largely on inferences from studies in other
regions, detritivory (which includes scavenging, deposit
feeding, and uptake of dissolved organic matter) predominates within the meiofauna of the California slope.
For example, deep-sea Foraminifera, as a group, consume phytodetritus and the remains of small animals,
sediment grains with associated bacteria and particulate
organic carbon, and, possibly, dissolved organic matter
(Gooday et al., 1992). The nematodes and harpacticoids
similarly appear to feed predominantly on detrital
particles, sediment and/or bacteria (e.g., Gage and
Tyler, 1991; J. Lambshead, personal communication),
although some are certainly predatory. Thus, a very
slim data base suggests that the California slope
meiofauna predominantly occupy low trophic levels.
In general, specialized predators appear to constitute