196
Craig R. SMITH and Amanda W.J. DEMOPOULOS
magnitude (i.e., 0.47 to 9.6 cm
2 y
−1 ). Similarly, within
the relatively homogeneous Santa Catalina Basin, C.R.
Smith et al. (1993) measured mixing coefficients for
234 Th ranging from 7.9 to 200 cm
2 y
−1 . This high
variability in mixing coefficients undoubtedly reflects
the high spatial variability in flux of particulate organic
carbon, faunal densities (especially the megafauna),
and individual activity rates known to occur in slope
habitats.
(3) Despite this high spatial heterogeneity, bioturbation coefficients on the northeast Pacific slope fit into a
broad environmental pattern, generally decreasing with
ocean depth (Smith and Rabouille, 2002). For example,
the maximum bioturbation coefficient measured for
210 Pb on the northeast Pacific slope (9.8 cm
2 y
−1 :
Carpenter et al., 1982) is an order of magnitude
less than the maximum measured in shallow-water
habitats (370 cm
2 y
−1 : Carpenter et al., 1985) and about
10-fold greater than the maximum in the abyssal Pacific
(0.9 cm
2 y
−1 : Table 6.1). Similarly, the minimum bioturbation coefficient measured on the Pacific slope falls
between the minima for the shallow-water and abyssal
habitats. Again, this is very likely a function of flux
rates of particulate organic carbon, the abundance and
biomass of macro- and megabenthos, and presumably
the activity rates of animals, which decrease roughly by
an order of magnitude from the shelf to the slope, and
again from the slope to the oceanic abyss (Table 6.1:
see also Smith and Rabouille, 2002).
One final feature of bioturbation is worth mentioning. In low-energy habitats (i.e., those without
erosive water currents), animal activities, especially the
crawling of epibenthic megafauna, erase the tracks and
trails of other animals (Wheatcroft et al., 1989). In
the Santa Catalina Basin on the California margin,
millimeter-scale animal traces persist for only days to
weeks before being erased by an abundant and active
megafauna (Wheatcroft et al., 1989). In the abyssal
equatorial Pacific, similar structures persist for more
than four months (Gardner et al., 1984). Once again,
this no doubt reflects the high flux rates for particulate
organic carbon, faunal standing crops, and mean rates
of animal activity on the Pacific slope relative to the
more energy-poor, open-ocean abyss.
Experimental studies of recolonization provide insights into natural processes structuring seafloor assemblages, and the response of such communities
to anthropogenic disturbance (e.g., bottom trawling,
seafloor mining, waste disposal). Three types of manipulations have been used in studies of recolonization
on the California slope: (1) trays of azoic sediment;
(2) creation of artificial mounds; and (3) implacement
of food falls (dead fish and whale carcasses). Sedimenttray experiments at a depth of 1300 m in the Santa
Catalina Basin yielded very low rates of recolonization,
with macrofaunal abundance attaining only ~3% of
that in the background community after 4.5 months
(Levin and Smith, 1984). Sediment-tray colonization
rates are likely to be biased downward, however, by
excluding burrowers and altering flow structure over
the seafloor (Kukert and Smith, 1992). Sites of burial
disturbance in the Santa Catalina Basin, resulting from
the creation of artificial mounds 5 cm high, were
colonized much more rapidly, with macrofaunal community abundance approaching background levels after
11 months (Kukert and Smith, 1992). Nonetheless,
even after 23 months, infaunal community structure
on artificial mounds differed from that in surrounding
sediments, in particular having higher species richness;
thus, community succession continued for at least
two years following small-scale burial disturbance at
this site. Recolonization following carrion enrichment
and scavenger disruption of sediments in the Santa
Catalina Basin, and at a depth of 1240 m in the
San Diego Trough, exhibited at least two phases.
Within weeks to months, there were high densities
of opportunistic species, including cumaceans immigrating as adults to fish falls (C.R. Smith, 1986) and
dorvilleid and chrysopetalid polychaetes recruiting to
sediments within 2 m of whale falls (Smith and Baco,
1998). Colonization rates by opportunists following
whale-fall enrichment are the most rapid measured
below 1000 m in the ocean, with dorvilleids and
chrysopetalids attaining densities of 20 000 individuals m
−2 within four months. The re-establishment
of background assemblages following intense local
enrichment of California margin sediments appears
to occur very slowly, however, with macrofaunal
community structure remaining anomalous around a
whale carcass in the 1900-m-deep San Clemente
Basin 2.6 years after emplacement (Smith and Baco,
unpublished data).
It is noteworthy that recolonization following meterscale sediment disturbance and enrichment on the
California slope often follows patterns similar to those
in shallow water, with, for instance, initial colonization
by opportunistic cumaceans and dorvilleids (Zmarzly
et al., 1994; Vetter, 1996). However, rates of colonization generally are markedly slower at these bathyal
depths, with complete community recovery requiring
Craig R. SMITH and Amanda W.J. DEMOPOULOS
magnitude (i.e., 0.47 to 9.6 cm
2 y
−1 ). Similarly, within
the relatively homogeneous Santa Catalina Basin, C.R.
Smith et al. (1993) measured mixing coefficients for
234 Th ranging from 7.9 to 200 cm
2 y
−1 . This high
variability in mixing coefficients undoubtedly reflects
the high spatial variability in flux of particulate organic
carbon, faunal densities (especially the megafauna),
and individual activity rates known to occur in slope
habitats.
(3) Despite this high spatial heterogeneity, bioturbation coefficients on the northeast Pacific slope fit into a
broad environmental pattern, generally decreasing with
ocean depth (Smith and Rabouille, 2002). For example,
the maximum bioturbation coefficient measured for
210 Pb on the northeast Pacific slope (9.8 cm
2 y
−1 :
Carpenter et al., 1982) is an order of magnitude
less than the maximum measured in shallow-water
habitats (370 cm
2 y
−1 : Carpenter et al., 1985) and about
10-fold greater than the maximum in the abyssal Pacific
(0.9 cm
2 y
−1 : Table 6.1). Similarly, the minimum bioturbation coefficient measured on the Pacific slope falls
between the minima for the shallow-water and abyssal
habitats. Again, this is very likely a function of flux
rates of particulate organic carbon, the abundance and
biomass of macro- and megabenthos, and presumably
the activity rates of animals, which decrease roughly by
an order of magnitude from the shelf to the slope, and
again from the slope to the oceanic abyss (Table 6.1:
see also Smith and Rabouille, 2002).
One final feature of bioturbation is worth mentioning. In low-energy habitats (i.e., those without
erosive water currents), animal activities, especially the
crawling of epibenthic megafauna, erase the tracks and
trails of other animals (Wheatcroft et al., 1989). In
the Santa Catalina Basin on the California margin,
millimeter-scale animal traces persist for only days to
weeks before being erased by an abundant and active
megafauna (Wheatcroft et al., 1989). In the abyssal
equatorial Pacific, similar structures persist for more
than four months (Gardner et al., 1984). Once again,
this no doubt reflects the high flux rates for particulate
organic carbon, faunal standing crops, and mean rates
of animal activity on the Pacific slope relative to the
more energy-poor, open-ocean abyss.
Experimental studies of recolonization provide insights into natural processes structuring seafloor assemblages, and the response of such communities
to anthropogenic disturbance (e.g., bottom trawling,
seafloor mining, waste disposal). Three types of manipulations have been used in studies of recolonization
on the California slope: (1) trays of azoic sediment;
(2) creation of artificial mounds; and (3) implacement
of food falls (dead fish and whale carcasses). Sedimenttray experiments at a depth of 1300 m in the Santa
Catalina Basin yielded very low rates of recolonization,
with macrofaunal abundance attaining only ~3% of
that in the background community after 4.5 months
(Levin and Smith, 1984). Sediment-tray colonization
rates are likely to be biased downward, however, by
excluding burrowers and altering flow structure over
the seafloor (Kukert and Smith, 1992). Sites of burial
disturbance in the Santa Catalina Basin, resulting from
the creation of artificial mounds 5 cm high, were
colonized much more rapidly, with macrofaunal community abundance approaching background levels after
11 months (Kukert and Smith, 1992). Nonetheless,
even after 23 months, infaunal community structure
on artificial mounds differed from that in surrounding
sediments, in particular having higher species richness;
thus, community succession continued for at least
two years following small-scale burial disturbance at
this site. Recolonization following carrion enrichment
and scavenger disruption of sediments in the Santa
Catalina Basin, and at a depth of 1240 m in the
San Diego Trough, exhibited at least two phases.
Within weeks to months, there were high densities
of opportunistic species, including cumaceans immigrating as adults to fish falls (C.R. Smith, 1986) and
dorvilleid and chrysopetalid polychaetes recruiting to
sediments within 2 m of whale falls (Smith and Baco,
1998). Colonization rates by opportunists following
whale-fall enrichment are the most rapid measured
below 1000 m in the ocean, with dorvilleids and
chrysopetalids attaining densities of 20 000 individuals m
−2 within four months. The re-establishment
of background assemblages following intense local
enrichment of California margin sediments appears
to occur very slowly, however, with macrofaunal
community structure remaining anomalous around a
whale carcass in the 1900-m-deep San Clemente
Basin 2.6 years after emplacement (Smith and Baco,
unpublished data).
It is noteworthy that recolonization following meterscale sediment disturbance and enrichment on the
California slope often follows patterns similar to those
in shallow water, with, for instance, initial colonization
by opportunistic cumaceans and dorvilleids (Zmarzly
et al., 1994; Vetter, 1996). However, rates of colonization generally are markedly slower at these bathyal
depths, with complete community recovery requiring