Ecology, 89(4), 2008, pp. 991–1000
? 2008 by the Ecological Society of America
COMMUNITY CHANGE IN THE VARIABLE RESOURCE HABITAT
OF THE ABYSSAL NORTHEAST PACIFIC
HENRY A. RUHL1
Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039 USA
from random ecological drift in natural systems has been limited. Evidence for nonrandom,
resource-driven change is presented here for an epibenthic megafauna community in the
abyssal northeast Pacific Ocean from 1989 to 2004. The sinking particulate organic carbon
food supply is linked not only to species-specific abundances, but also to species composition
and equitability. Shifts in rank abundance distributions (RADs) and evenness, from more to
less equitable, correlated to increased food supply during La Nin ˜ a phases of the El Nin ˜ o
Southern Oscillation. The results suggest that each taxon exhibited a differential response to a
sufficiently low dimension resource, which led to changes in community composition and
equitability. Thus the shifts were not likely due to random ecological drift. Although the
community can undergo population-level variations of one or more orders of magnitude, and
the shape of the RADs was variable, the organization retained a significant consistency,
providing evidence of limits for such changes. The growing evidence for limited resource-
driven changes in RADs and evenness further emphasizes the potential importance of
temporally variable disequilibria in understanding why communities have certain basic
Research capable of differentiating resource-related community-level change
Term Ecological Research (LTER); megafauna; niche hierarchy; ophiuroid; pelagic–benthic coupling; rank
abundance; relative abundance.
California Current Ecosystem (CCE); climate; deep sea; echinoderm; holothuroid; Long-
The vast majority of research on the potential
influences of either resources or dispersal and recruit-
ment in community structuring explicitly examines or
assumes steady-state conditions (e.g., Motomura 1932,
Preston 1948, MacArthur 1957, Whittaker 1965, Mac-
Arthur and Wilson 1967, May 1975, Hubbell 1979, 2001,
Sugihara 1980, Tokeshi 1990, 1999, Chase and Liebold
2003, Olding-Smee et al. 2003, Sugihara et al. 2003).
Over interannual time scales, however, variations in
climate clearly impact marine and terrestrial populations
worldwide through pulsed and pressed forcing (e.g.,
Stenseth et al. 2002). Long-term studies in the California
Current Ecosystem (CCE) region and greater northeast
(NE) Pacific Ocean, for instance, have shown relation-
ships between climatic and environmental conditions
and shifts in productivity, zooplankton, and fish
abundances (McGowan et al. 1998, Hare and Mantua
2000). Further research has continued to examine how
environmental variation can lead to such changes and
how shifts might be distinguished from random ecolog-
ical drift (e.g., Mantua 2004, Hsieh et al. 2005).
Several mechanisms have been developed to explain
how the pervasive trends in the relative abundance of
species are shaped and maintained, including theories
based on niches, dispersal, and stochastic processes.
Rank abundance distributions (RADs) and equitability
are widely thought to be indicators of how a resource or
resources are divided up by a particular guild or
community (e.g., Motomura 1932, MacArthur 1957,
Whittaker 1965, Sugihara 1980, Tokeshi 1990, 1999,
Chase and Liebold 2003). Equitability has also been
linked to differences in hierarchical resource partitioning
(Sugihara et al. 2003). Neutral ecological theory (Hub-
bell 2001), a type of dispersal structuring, has provided a
comprehensive null model for such niche-based theories.
Many recent studies have evaluated hypotheses based
on niche and neutral theories of relative abundance in
both the context of evolution and contemporary ecology
(Gaston and Chown 2005, Pandolfi 2006). A number of
complications commonly limit unequivocal interpreta-
tion as to whether one or the other is dominant (Willis
and Whittaker 2002), including the covariation of
species distributions, geographic range, and environ-
mental gradients (Gilbert and Lechowicz 2004); the
pooling of spatial or temporal variability (Thibault et al.
2004); and the notion that many factors can potentially
affect individual-level to species-level success.
Interpreting temporal dynamics from natural systems,
where environment and resource variation can signifi-
cantly affect a species and vice versa, has also had
limitations (e.g., Brown et al. 2001, Chase and Liebold
2003), but temporal concepts have emerged that are
relevant here. Shifts in the abundance at the population
Manuscript received 6 December 2006; revised 10 July 2007;
accepted 3 August 2007. Corresponding Editor: C. W. Fox.
level of one taxon over time are often linked with either
influencing or response variables (e.g., Ernest and
Brown 2001), and variation can facilitate coexistence
of similar species maintaining diversity (Connell 1978,
Levins 1979). For example, local disturbance can reduce
local diversity but provide greater habitat diversity at
larger scales. Variation is also important in that a species
can be risk averse, risk neutral, or risk taking with
regard to environmental or resource variability (Chase
and Liebold 2003, Chesson et al. 2004).
Empirically tracking relative abundance over time has
included the documentation of community changes
during forest succession (Bazzaz 1975) and shifts in
desert rodent communities (Thibault et al. 2004).
Additionally, a study of a marine fish community noted
that commonly occurring taxa had different relative
abundance dynamics than rarer taxa, and those differ-
ences were founded in basic life history attributes
(Magurran and Henderson 2003, Magurran 2007). In
aquatic systems, increases in nutrients have been shown
to lead to the dominance of certain algal taxa during
blooms (e.g., Coale et al. 1996, Smayda 1997, Vitousek
et al. 1997). Evenness has even been suggested to be an
indicator of eutrophication (e.g., Cottingham and
Carpenter 1998, Tsirtsis and Karydis 1998, Kitsiou
and Karydis 2000). Coexistence in diatoms has been
shown to be facilitated by fluctuating environmental
factors (Descamps-Julien and Gonzalez 2005). Other
results have shown that the nature of shifts in
equitability in marine macrophytes can depend on
whether the system is open or isolated (Nielsen 2003).
As Magurran (2007) noted though, the empirical study
of temporal dynamics in relative abundance warrants
substantially greater attention.
The dynamics of an abyssal megafauna community
were examined here within the context of niche and
neutral theories of community structuring. Overall, the
abyssal environment at the study site in the NE Pacific
(Station M; 4100 m depth; 348500N, 1238000W) has
been relatively stable, with no sunlight, temperatures
around 1.58C, and relatively consistent prevailing
currents and dissolved O2when compared to shallower
marine habitats (Beaulieu and Baldwin 1998). The food
supply, however, is now known to vary over seasonal
and interannual scales (Baldwin et al. 1998, Smith et al.
2006), but there is no major feedback mechanism for
abyssal consumers to affect surface productivity within
the timescales examined here. The habitat at the scale of
the mobile megabenthos at the abyssal site can thus be
seen as less variable in environmental and resource
parameters when compared to more dynamic sea surface
Studies at Station M have found climatically influ-
enced seasonal and interannual variations in surface
water productivity and subsequent sinking of particulate
organic carbon (POC) food supply to the seafloor from
1989 to 2004 (Baldwin et al. 1998, Smith et al. 2006).
Links from surface climate to POC flux and POC flux to
mobile epibenthic megafaunal abundances of several
species have previously been made at the site (Ruhl and
Smith 2004). On a species-specific basis, several holo-
thuroids such as Elpidia minutissima had significant
negative correlations with POC flux, and others such as
Abyssocucumis abyssorum had positive correlations.
Importantly, some taxa appeared to increase in abun-
dance during higher food supply conditions, while
others increase during lower food fluxes, suggesting that
the utilization of the resource was not equal. Similar
processes involving climate, pelagic–benthic coupling of
food resources, and subsequent changes in abyssal
benthic communities have been observed in the north-
east Atlantic Ocean as well (Billett et al. 2001, Gooday
2002, Wigham et al. 2003a).
Greater than 99% of the mobile epibenthic megafauna
observed during the 16-year period were from 10
echinoderm taxa: the holothuroids E. minutissima,
Peniagone diaphana, P. vitrea, A. abyssorum, Synallactes
profundi, Scotoplanes globosa, Oneirophanta mutabilis,
and Psychropotes longicauda; the echinoid Echinocrepis
rostrata; and the ophiuroids dominated by Ophiura
bathybia. Deposit-feeding echinoderm megafauna like
those here have been shown to selectively feed on fresh
phytopigments (Billett et al. 1988, Lauerman et al. 1997,
Ginger et al. 2001, Iken et al. 2001, Demopoulos et al.
2003) and to partition and differentially utilize the food
source in terms of their organic contents (Hudson et al.
2003, Wigham et al. 2003a, b). Specific organic com-
pounds have also been related to reproductive processes
in deep-sea holothuroids (Hudson et al. 2003, Wigham
et al. 2003b).
This study examined variations in the species compo-
sition, RADs, Pielou’s evenness, and interspecific body
size vs. abundance relationships of the top 10 most
dominant mobile epibenthic megafauna at Station M
from 1989 to 2004, a period of significant community
change and food supply variability. Addressed here is
the extent to which the community descriptors varied
over the study period and whether the variations were
essentially random or linked to the dominant resource
variable, POC flux.
The in situ setting, Station M, lies beneath the
California Cooperative Oceanic Fisheries Investigations
(CalCOFI) and the California Current Ecosystem Long-
term Ecological Research (CCE LTER) principal study
areas, and is subject to seasonal and interannual scale
variations in POC flux (Baldwin et al. 1998, Smith et al.
2006). These changes in flux are influenced, in part, by
climatic shifts expressed in the Northern Oscillation
Index (NOI; Schwing et al. 2002) and Bakun upwelling
index (BUI; Bakun 1973).
Abundance and body size estimates for the study were
collected using a camera sled system to conduct line
transect photography (Lauerman et al. 1996, Ruhl and
Smith 2004, Ruhl 2007). An otter trawl system was towed
HENRY A. RUHL 992Ecology, Vol. 89, No. 4
behind the sled to collect photographed specimens for
identification. Over the 16-year study, 52 transects
averaging 1.2 km in length were conducted during 37
monthly time intervals on a roughly seasonal basis. A
transect length weighted-abundance estimate was created
if more than one transect was conducted during any
particular month. Uneven temporal sampling and signif-
icant gaps in the time series exist due to logistical
and Genin (1987), Wakefield and Smithey (1989), Buck-
land et al. (1993), Laake et al. (1994), Lauerman et al.
(1996), Ruhl and Smith (2004), and Ruhl (2007).
The monthly POC flux data used for this analysis were
a composite of particle flux trap data collected at 50 m
and 600 m above bottom (mab) at the site, as well as
model estimated flux where trap data were unavailable.
The POC flux data were collected using a sedimentation
trap with a 0.25-m2opening with a 10-day sampling
interval (Baldwin et al. 1998, Smith et al. 2006). The
primary data for the composite were the 50-mab trap
data. Where available, 600-mab trap data were used to
fill in any gaps in the 50-mab POC flux data. An
empirical model for estimating POC flux to 50 mab at
the site was recently proposed that incorporates lagged
influences from satellite-estimated sea surface tempera-
ture and net primary production (sensu Laws 2004), sea
level air pressure anomalies (NOI), and regional
upwelling (BUI) (Smith et al. 2006). The model-
estimated flux could account for .50% of the observed
variation in the monthly estimates (see Supplement).
The model thus effectively differentiated between high
and low flux periods. Any remaining gaps in the POC
flux record were filled in using the model estimates. The
resulting composite represents the best information
available on the monthly POC flux to the study site,
and use of the composite here avoided the complexities
of cross-correlating two data sets with multiple gaps.
Rank abundance distributions (RADs) were created
for each sampling time by ranking the abundances of the
10 most dominant taxa in descending order, with rank
one being most abundant. Species composition is
characterized here using species-specific densities. The
Bray-Curtis similarity index was used to create similarity
matrices for the RADs and species composition data
with a log(xþ1) transformation. These matrices then
served as input for the similarity vs. time lag scatter plots
(Fig. 1A, B), hierarchical similarity dendrograms using
group average clustering (Fig. 1C, D), and nonmetric
multidimensional scaling (MDS) x-ordinations (Fig.
An analysis of similarity (ANOSIM), with 999
permutations, was used to determine if deviations in
either POC food supply or climate were related to either
the RAD or species composition similarities. ANOSIM
is a randomization test for differences between groups
separated by specified factors and is similar to an analysis
of variance (ANOVA). These nonparametric, multivar-
iate analyses were conducted using the PRIMER-5
software package (PRIMER-E, Lutton, Devon, UK).
Additionally, a Mantel randomization test was used
to evaluate the significance of the RAD and species
composition similarity shifts over time (Fig. 1A, B),
since there are many more pairwise comparisons
between sampling times than actual sample times.
Cross-correlations between the RAD and species com-
position similarity MDS x-ordinates, evenness, and the
POC flux composite were conducted using the nonpara-
metric Spearman rank correlation. All correlations were
conducted using monthly data with POC flux changes
preceding megafauna sample shifts.
Directional changes in both the rank abundance
distribution (RAD) and species composition were
evident from 1989 to 2004, with samples taken at closer
time intervals being more similar than samples taken
with longer temporal lags between them (P , 0.001, Fig.
1A, B). A partial convergence, or a return direction to
starting similarity, might have even begun in the longer
lags of species composition similarity (Fig. 1B, Supple-
ment). The significantly lower slope of the RAD plot,
when compared to species composition, was at least
partially due to the fact that some variability is lost when
ranking the species abundance data. Further analysis
was able to illustrate the degree to which the RADs had
Similarity dendrograms for the RAD and species
composition illustrate that while similar RAD distribu-
tions were found at a variety of times, the species
composition dendrogram had temporally oriented sim-
ilarity clusters, including 1989–1998 and 2001–2004 (Fig.
1C, D). Other notable species composition clusters
included observations from 1989 to August 1994 and
September 1994 to 1998, but the two groups were not
temporally exclusive, since June 1992 clusters into the
otherwise September 1994–1998 group (Fig. 1D, Sup-
plement). Also of note is that the principal change in
species composition after the 1997–1999 El Nin ˜ o/La
Nin ˜ a discussed in Ruhl and Smith (2004) has persisted
Time series plots of the RAD and species composition
similarity, as well as evenness over time illustrate
changes that occurred over months to years, and each
community descriptor had time-lagged links to partic-
ulate organic carbon (POC) flux (Fig. 2A–D). Signifi-
cant correlations with the POC food supply existed, with
peaks at 10–12 months for the RAD (Spearman rank
correlation [rS]¼0.38, P , 0.05), 12 months for evenness
(rS¼ 0.33, P ¼ 0.05), and 10–13 months for species
composition (rS¼ 0.48, P , 0.01). A temporal lag of
many months is sensible considering that while the
community can respond with rapid changes in activity
(Kaufmann and Smith 1997, Bett et al. 2001), it appears
to take several months or more for a shift in resources to
lead to observable changes in abundance resulting from
April 2008 993ABYSSAL RESOURCES AND COMMUNITY CHANGE
from 1989 to 2004 and (B) all possible monthly species composition pairs vs. the time (in months) between the compared samples.
Also plotted on (A) and (B) (solid lines) are the best linear fits of the monthly data, with 95% confidence intervals in parentheses
and randomization test P values. Discrete 12-month averages of similarity are also presented using large black circles. The reduced
variation and slope in (A) relative to (B) are to some extent the result of ordering the compositional data by rank instead of taxon.
Also shown are Bray-Curtis similarity dendrograms of (C) monthly RADs and (D) monthly species composition. All are based on
monthly abundance estimates of the 10 most dominant epibenthic megafauna taxa observed from 1989 to 2004.
Scatter plots (small open circles) of Bray-Curtis similarity for (A) all possible rank abundance distribution (RAD) pairs
HENRY A. RUHL 994Ecology, Vol. 89, No. 4
processes such as reproduction, recruitment, biotic
interactions, and mortality (Ruhl and Smith 2004).
The RADs and evenness exhibited significant covaria-
tion (rS¼ 0.82, P , 0.001). Although both the RAD
similarity and evenness were correlated to species
composition during certain periods, the correlation
was insignificant for the whole time series, providing
evidence that equitability may have had some indepen-
dence from species composition. The ANOSIM test
results supported the cross-correlations and showed that
the RAD and species composition distributions were
significantly different (P , 0.05) during times when the
annual POC flux was above and below the long-term
average and when the Northern Oscillation Index (NOI)
condition was above and below zero.
The monthly RADs throughout the time series from
1989 to 2004 had an approximately geometric distribu-
tion (Fig. 3A), with each rank switching between one
and six times and the middle ranks experiencing the
most variability. When the monthly RADs were
grouped by the principal communities outlined in Fig.
1D, they all had similar slopes (Fig. 3B–E). Even with
observed directional changes that were linked with
evenness and resource availability, the relative abun-
dances in each lower-density rank were typically less
abundant by roughly one-half. The continuity in RAD
shape for the different species compositions suggests
that shifts in RADs were limited. It is tempting here to
try to discern what RAD model best fits the observa-
tions, be it geometric (Motomura 1932), sequential
breakage (Sugihara 1980), or another. The implications
here, however, do not rely on any particular distribu-
tion. There are often subtle differences between such
distributions and subsequent models, especially for a
small assemblage (Sugihara 1980, Tokeshi 1999).
Interspecific body size vs. abundance also had
significantly (P , 0.05) consistent negative correlation
slopes between the entire study period and the principal
measured by the multidimensional scaling (MDS) x-ordinate, as well as (B) Pielou’s evenness, (C) species composition relative
similarity MDS x-ordinate, and (D) particulate organic carbon (POC) flux (mg C?m?2?d?1) composite. The monthly data are
plotted as open circles for the community descriptors and a dashed line for POC flux. All have a 13-month running mean shown as
a solid black line. All correlations were conducted using monthly data. The 13-month centered running means are for display
Time series plots showing (A) the Bray-Curtis rank abundance distribution (RAD) relative similarity over time as
April 2008 995 ABYSSAL RESOURCES AND COMMUNITY CHANGE
temporal clusters (Fig. 4A–E). The abundances of
several taxa changed by one or more orders of
magnitude between the different temporal groupings,
but the slopes were similar for each of the periods with
different species compositions (Fig. 4A–E).
Niche theory envisions that the abundance of a
species is a result of the availability of a multidimen-
sional mix of resources, such as energy and space (e.g.,
Hutchinson 1957, Chase and Leibold 2003). Differential
responses to resource variability are thought to be one
way competitive exclusion can be prevented. The
broken-stick analogy (MacArthur 1957) and its modi-
fications have led to a niche hierarchy model in which
the total resource, or stick, is sequentially broken, with
the length of each piece representing the relative
abundance of each species utilizing the common
resource. Furthermore, the overall equitability in the
size of the pieces, and thus relative abundances, has been
linked to resource type, with more evenness being
representative of a more even utilization of a high-
(A) 1989–2004, (B) 1989–August 1994, (C) September 1994–1998, (D) 1989–1998, and (E) 2001–2004. Below each abundance rank
(1–10) is the taxon that dominated that rank during each principal species composition time. Above each panel are the 95%
confidence intervals for the slope and intercept of the linear descriptions, as well as the r2and P value. Each point represents a
species-specific monthly estimate for all size classes. It is important to note that the values are ranked, and thus significant
correlations are not remarkable in each separate panel. The most relevant aspect of the statistics is the similarity of the linear
descriptions among the panels. Species are Ophiura spp., Elpidia minutissima, Peniagone diaphana, Peniagone vitrea, Echinocrepis
rostrata, Abyssocucumis abyssorum, Synallactes profundi, Scotoplanes globosa, Oneirophanta mutabilis, and Psychropotes
The five panels show ranked monthly log-transformed abundances (originally measured as individuals/m2) for
HENRY A. RUHL996 Ecology, Vol. 89, No. 4
dimension resource and less equitable with a more basic,
low-dimension resource (Sugihara et al. 2003). Neutral
theory, conversely, can produce some pervasive patterns
in ecology, such as species–area and rank–abundance
distributions, with no requirements for the differential
utilization of resources (Hubbell 2001).
At Station M there is now compelling evidence for
seasonal and interannual variation in food supply
resulting in interannual resource disequilibria (Smith
and Kaufmann 1999, Smith et al. 2006). Predictions of
niche theory were reevaluated here within the context of
the fluctuating resource environment of the northeast
(NE) Pacific abyssal seafloor. If each taxon had an
equivalent per capita response to a variable resource,
then any measured shift in rank abundance distributions
(RADs), evenness, and species composition would be
due to random ecological drift, and links between food
supply and the relative community descriptors should be
insignificant, regardless of any overall change in
abundance or biomass. Alternatively, if each taxon
exhibited a unique response to a sufficiently low-
dimension resource, then nonrandom links between
community shifts and food supply could be detectable,
and potentially include rank switching and local
extinctions and recolonizations (Brown et al. 2001).
Shifts in the RADs, evenness, and species composition
were significantly linked to the particulate organic
carbon (POC) food supply at Station M, suggesting at
least a partially deterministic role for life history
processes in community dynamics at the site. Several
taxa appeared to have opposing responses to long-term
food supplies (Ruhl and Smith 2004), and resource
utilization trade-offs have been demonstrated for several
congeneric taxa (Hudson et al. 2003, Neto et al. 2006).
Links between the RADs and evenness also indicated
that more eutrophic conditions led to more asymmetric
RADs and lower evenness, which is expected under
niche hierarchy (Sugihara et al. 2003). Changes in
surface conditions above Station M (e.g., Kahru and
Mitchell 2002, Lavaniegos and Ohman 2003) inextrica-
bly lead to variation in the composition of POC flux
material. If hierarchical partitioning of resources is
occurring at Station M, such resource division would
expectedly include the species-level preferences for
specific pigments, and lipids observed in congeneric
taxa for (A) 1989–2004, (B) 1989–August 1994, (C) September 1994–1998, (D) 1989–1998, and (E) 2001–2004. Above each panel
are the 95% confidence intervals for the slope and intercept of the linear descriptions, as well as the r2and P value. Each point
represents a species-specific monthly estimate for all size classes. The most relevant aspect of the statistics is the similarity of the
linear descriptions among the panels.
The five panels show monthly log-transformed abundance (individuals/m2) vs. mean body size (length in mm) for all 10
April 2008 997 ABYSSAL RESOURCES AND COMMUNITY CHANGE
taxa in the NE Atlantic (Hudson et al. 2003, Wigham et
al. 2003a, b).
The degree to which a population can track a
dominant forcing variable has been suggested to depend
on whether the timescales of the dominant forcing and
organism generation time are similar (Hsieh and Ohman
2006). The apparent interannual scale of the variation in
the taxon-specific densities and community changes here
suggest that generation times are roughly interannual as
well. Increases in megafauna abundance at Station M
were significantly correlated with increases in smaller
size classes, indicating that reproduction and/or recruit-
ment influenced local increases in abundance (Ruhl
2007). Decreases in density, on the other hand, likely
resulted from inferior biotic interactions, decreased
fitness, and mortality. Even though Peniagone spp. are
known to exhibit swimming behavior, the mass migra-
tion of adult stages over thousands of meters is not
reasonable for most taxa in the study (Ruhl 2007).
A long-term study of desert rodents also found
directional shifts in RADs similar to that illustrated in
Fig. 1A without major changes in species richness
(Thibault et al. 2004). In both the rodent and abyssal
megafaunal analyses, the RADs have shifted within the
context of resource change. When the Station M RADs
are examined for the principal species composition
clusters, however, there is no persuasive evidence for
fundamental changes between the slopes of the ranked
abundances. This limit to variation is sensible within the
context of a hierarchical system that allows for shifts in
relative abundance and equitability related to changes in
The relationships between body size and abundance
were also relatively stable for the different community
compositions, providing additional context for the limits
of the community-level shifts at the site. Larger
holothuroids, such as P. longicauda and O. mutabilis,
varied in abundance by an order of magnitude but did
not become more abundant than the smaller Peniagone
spp. Smaller animals have been seen to be more
abundant, in part because they require less resource
per unit area (West et al. 1997), and body size has been
linked to energy use and community structure (Ernest
2005). Southwood et al. (2006) recently illustrated how
body size vs. abundance, body size vs. area, and species–
area relationships are all interrelated in vertebrates,
suggesting that a formal niche space exists. Further
research could also unite such relationships in inverte-
brate groups. The importance of internal resource
distribution and other mechanisms regulating body size
and abundance relationships continues to be debated
(Brown et al. 2005), but the results here are indicative of
some stability in such a relationship, even with
significant species composition and resource change.
The limits to the changes observed in this study were
probably a reflection of the limits of ecological plasticity
in processes such as resource utilization, dispersal, and
Results from megafauna at Station M indicate that
both individual populations and community descriptors
like the RADs and evenness were linked to resource
availability. The overall relative megafauna abundances
found at Station M were similar to distributions
expected when a single or few factors, such as POC flux
quantity and quality, control community structure (Figs.
3, 4). The asymmetric shape of the RADs and their link
to POC flux provide further evidence that food supply
from overlying surface waters is a key variable in the
deep sea. Fluctuations in abyssal abundances have now
been observed in smaller protist and metazoan taxa
(Drazen et al. 1998, Gooday 2002) and invertebrate
megafauna (Billett et al. 2001, Ruhl and Smith 2004), as
well as in higher trophic-level fishes (Bailey et al 2006).
Multiyear disparities between food supply and demand
for smaller sediment-based organisms (Smith and
Kaufmann 1999) suggest that imbalances are forcing
community processes at other guilds and trophic levels
at the site. Benthic fauna mediate carbon cycle dynamics
through the bioturbation of surface sediments (Reimers
et al. 1992, Kaufmann and Smith 1997, Bett et al. 2001,
Solan et al. 2004). Community changes like the one
described here could be influencing the proportion of
sinking POC that remains in the contemporary carbon
cycle or is geologically sequestered.
The results here support theories that include
disequilibria in modulating community diversity and
relative abundance (Connell 1978, Levins 1979, Grassle
1989, Chesson and Huntly 1997, Chesson 2000, Chesson
et al. 2004). Climate variations such as the El Nin ˜ o
Southern Oscillation and the North Atlantic Oscillation
have cycles that direct systems away from equilibrium
over interannual scales for much of the world biome.
Interannual scale variations occur within the context of
decadal and greater scale fluctuations, and treatment of
climate oscillations as discrete historical events belies
their pervasive and ever-present ecological effects.
Testing of community structuring theories within a
temporal as well as spatial context should continue to
highlight the salient aspects of current structuring
Special thanks to K. Smith and the current and past
members of the research team studying Station M, including
R. Baldwin, F. Uhlman, J. Ellena, R. Glatts, M. Kirk, M.
Vardaro, D. Bailey, S. Beaulieu, R. Kaufmann, L. Lovell, and
R. Wilson, with additional assistance from the Scripps
Institution of Oceanography Benthic Invertebrate Collection,
the shipboard technical support group and crew of the R/V
New Horizon, the California Cooperative Oceanic Fisheries
Investigations (CalCOFI), and the California Current Ecosys-
tem Long-term Ecological Research (CCE LTER) programs. I
also thank L. Levin, G. Sugihara, D. Phillips, D. Cayan, and
M. Ohman for their guidance and support throughout this
long-term research, and C. McClain and two anonymous
reviewers for helpful comments on the manuscript. Funding
was supported by National Science Foundation grant numbers
OCE 89-22620, OCE92-17334, OCE98-07103, OCE00-02385,
OCE02-42472, and the David and Lucille Packard Foundation.
HENRY A. RUHL998 Ecology, Vol. 89, No. 4
Bailey, D. M., H. A. Ruhl, and K. L. Smith, Jr. 2006. Long-
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