a synthesis of bentho-pelagic coupling on the antarctic ...€¦ · bentho-pelagic coupling clearly...

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Deep-Sea Research II 53 (2006) 875–894

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A synthesis of bentho-pelagic coupling on the Antarctic shelf:Food banks, ecosystem inertia and global climate change

Craig R. Smitha,�, Sarah Mincksa, David J. DeMasterb

aDepartment of Oceanography, University of Hawaii at Manoa, Honolulu, 1000 Pope Road, HI 96822, USAbDepartment of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA

Received 9 December 2004; accepted 27 February 2006

Available online 30 June 2006

Abstract

The Antarctic continental shelf is large, deep (500–1000m), and characterized by extreme seasonality in sea-ice cover

and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-

pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such

coupling to be weak. Here, we address six questions regarding the nature and strength of coupling between benthic and

water-column processes on the continental shelf surrounding Antarctica. We find that water-column production is

transmitted to the shelf floor in intense pulses of particulate organic matter, although these pulses are often difficult to

correlate with local phytoplankton blooms or sea-ice conditions. On regional scales, benthic habitat variability resulting

from substrate type, current regime, and iceberg scour often may obscure the imprint of water-column productivity on the

seafloor. However, within a single habitat type, i.e. the muddy sediments that characterize much of the deep Antarctic shelf,

macrobenthic biomass appears to be correlated with regional primary production and sea-ice duration. Over annual time-

scales, many benthic ecological processes were initially expected to vary in phase with the extraordinary boom/bust cycle of

production in the water column. However, numerous processes, including sediment respiration, deposit feeding, larval

development, and recruitment, often are poorly coupled to the summer bloom season. Several integrative, time-series

studies on the Antarctic shelf suggest that this lack of phasing may result in part from the accumulation of a persistent

sediment food bank that buffers the benthic ecosystem from the seasonal variability of the water column. As a

consequence, a variety of benthic parameters (e.g., sediment respiration, inventories of labile organic matter, macrobenthic

biomass) may act as ‘‘low-pass’’ filters, responding to longer-term (e.g., inter-annual) trends in water-column production.

Bentho-pelagic coupling clearly will be altered by Antarctic climate change as patterns of sea-ice cover and water-column

recycling vary. However, the nature of such climate-driven changes will be very difficult to predict without further studies

of Antarctic benthic ecosystem response to (1) inter-annual variability in export flux, and (2) latitudinal gradients in

duration of sea-ice cover and benthic ecosystem function.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Antarctic shelf; Bentho-pelagic coupling; Organic carbon flux; Climate change; Food banks; Benthos

front matter r 2006 Elsevier Ltd. All rights reserved

r2.2006.02.001

ng author. Tel.: +1808 956 7776;

9516.

ss: [email protected] (C.R. Smith).

1. Introduction

Connections between ecological processes in thewater column and seafloor are widely recognized in

.

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ARTICLE IN PRESSC.R. Smith et al. / Deep-Sea Research II 53 (2006) 875–894876

continental-shelf ecosystems (e.g., Graf, 1992) andare called ‘‘bentho-pelagic coupling.’’ In this synth-esis, we use the term bentho-pelagic coupling to meana causal relationship (rather than simply a correla-tion) between water-column and benthic processes.When water-column processes exert control on thebenthos, the coupling is said to be ‘‘downward.’’Common examples of downward coupling includecontrol of seafloor respiration and biomass by thesinking flux of particulate organic matter (Graf,1992; Smith et al., 1997). ‘‘Upward’’ couplingoccurs when benthic processes causally influenceecosystem dynamics in the water column, forexample, when organic-matter mineralization ortrace-metal entrainment at the seafloor supplieslimiting nutrients to the euphotic zone (Sedwicket al., 2000). Here, we will focus on downwardcoupling although we will briefly consider upwardprocesses.

Many lines of evidence suggest that bentho-pelagic coupling can substantially influence materialcycles, community dynamics, and fisheries yields inshelf ecosystems. For example, particle-flux studiesin a variety of shelf habitats indicate that 6–60% ofnet annual primary production can reach theseafloor (Valiela, 1984), providing food for keycomponents of benthic food webs such as suspen-sion feeders, deposit feeders, and sediment mi-crobes. Much of global fisheries yield (roughly33%, Pauly and Christensen, 1995) and a significantpercentage of coastal ecosystem biomass, arecomposed of demersal or benthic species that utilizeenergy from this pelagic rain. The deposition ofpelagic production (combined with riverine inputsof terrestrial production) cause continental shelfsediments to be major sites of organic mattermineralization and nutrient regeneration in theocean (Jahnke and Jackson, 1992). The sinking ofmaterials produced in the water column (e.g.,downward bentho-pelagic coupling) also allowsthe shelf floor to accumulate phytoplankton bio-markers and to develop benthic communities thatreflect production processes in the waters above.Thus, as a direct consequence of downwardcoupling, shelf sediments and their biotic commu-nities can provide integrated views in space and timeof ecosystem dynamics in the pelagic realm. Con-sequently, benthic studies may yield importantinsights into climate-driven changes in coastalpelagic ecosystems.

The vast Antarctic continental shelf, whichencompasses roughly 11% of global shelf area

(Clarke and Johnston, 2003), has several character-istics that might cause bentho-pelagic coupling to beweak compared to other regions (including theArctic). The Antarctic shelf is unusually deep(500–1000m) due to ice loading on the continent(Clarke and Johnston, 2003), and it is characterizedby complex topography and ocean circulation(Hofmann and Klinck, 1998; Smith et al., 1999).These properties are expected to reduce the strengthof bentho-pelagic coupling by increasing the sinkingtime and recycling of pelagic production in thewater column, and by allowing local benthic habitatvariability to obscure pelagic signals. However,other properties of Antarctic shelf ecosystems mayenhance the relative importance of bentho-pelagiccoupling. For example, summer–winter variationsin sunlight, sea-ice cover, and water-column strati-fication produce extraordinary seasonality in pela-gic primary production in Antarctica, yieldingintense summer phytoplankton blooms that mayyield mass settling of phytoplankton and highexport ratios. The accumulation of high algalbiomass within sea ice also may favor efficienttransport of primary production to the seafloorbecause algae released from melting sea ice tend toaggregate and sink (Riebesell, 1991). In addition,pelagic food webs in Antarctic shelf waters can berelatively short, with diatom blooms being con-sumed by krill, which in turn produce fecal pelletsthat sink rapidly to the seafloor (Wefer et al., 1988;Bathmann et al., 1991). In fact, benthic biomass inAntarctic shelf waters can be very high (Gerdes etal., 1992; Arntz et al., 1994), suggesting efficienttransfer of water-column production to the benthos.Because of these opposing factors, it is difficult tosay a priori whether bentho-pelagic coupling on theAntarctic shelf should be stronger or weaker than inother regions.

To elucidate the nature of bentho-pelagic cou-pling on the Antarctic shelf, we will use the existingliterature and a new meta-analysis to address sixmajor questions.

(1)
Are water-column production signals rapidlytransmitted to the seafloor?
(2)
Do benthic parameters (e.g., biomass andrespiration) track regional variations in sea-icecover and water-column production?
(3)
Do benthic processes vary in phase withseasonal primary production and flux?
(4)
How do benthic ecosystems respond to parti-cular flux events or seasons?

ARTICLE IN PRESSC.R. Smith et al. / Deep-Sea Research II 53 (2006) 875–894 877

(5)

Fig.

seas

Feb

Are there examples of upward coupling (i.e., ofseafloor processes influencing the ecology of thewater column)?

(6)
Will the patterns of bentho-pelagic coupling inthe Antarctic be altered by climate change?
2. Question (1): Are water-column production signals

rapidly transmitted to the shelf floor?

Clearly, downward bentho-pelagic coupling couldbe especially strong on the Antarctic shelf if themelting of sea ice and the intense, but often short-lived, summer phytoplankton blooms cause rapidexport of particulate organic carbon (POC) to theshelf floor. Time-series sediment traps provide onemeans to assess the timing and intensity of POC fluxfrom the water column; Sediment traps have beendeployed extensively at depths X150m, i.e. belowthe euphotic zone, on the open continental shelf ofAntarctica. Major studies have focused on thewestern Antarctic Peninsula region (von Bodungenet al., 1986; Wefer et al., 1988; Karl and Tien, 1991;Karl et al., 1996, unpublished data; Palanques et al.,2002; Ducklow et al., 2006; Smith et al., in review),the Ross Sea (Dunbar et al., 1989, 1998; Nelsonet al., 1996; Collier et al., 2000) and the Weddell Sea(Bathmann et al., 1991). All these studies documentdramatic summer pulses of particulate-organic-

1. Particulate carbon flux at 150m depth in the Palmer LTER stud

onal and interannual variability (D. Karl, unpublished data). Note

ruary and March, i.e. 1–2 months after the disappearance of sea ic

matter flux to deep shelf waters and, by inference,to the shelf floor. Peak summer fluxes, whenintegrated over time-scales of weeks, frequentlyexceed winter lows by 1–3 orders of magnitude, withsummer flux patterns punctuated by brief eventslasting a few weeks and varying in timing andintensity from year to year (Fig. 1). Thus, there isstrong evidence that the Antarctic shelf benthosexperiences a seasonal boom/bust cycle of POC fluxresembling the boom/bust patterns of primaryproduction and phytoplankton biomass in the watercolumn (Smith and Sakshaug, 1990; Karl et al.,1996; Smith et al., 1996; Smith et al., 1998).

It is important to note, however, that while POCflux and primary production on the Antarctic shelfshare similar scales of temporal variability, fluxpulses to the shelf floor frequently are not obviouslycoupled to local sea-ice disappearance or overlyingphytoplankton blooms. For example, in 1990–1992,Dunbar et al. (1998) found maximum particle fluxesin the Ross Sea occurring from two to as many as 10weeks after local surface waters became ice free, andCollier et al. (2000) found peak flux in 1997occurring in late fall even after sea ice had returned(Fig. 2). This poor coupling between sea-icedisappearance, phytoplankton blooms, and fluxevents to the shelf floor should not be surprisingbecause the factors controlling phytoplankton

y area on the western Antarctic Peninsula shelf showing extreme

that many of the flux pulses occur late in the summer season in

e in waters overlying the trap.

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Fig. 2. Percent sea-ice cover in the area (lines) and organic-carbon fluxes to �200m depths (histograms) at two stations (MS-6 and MS-

7b) on the Ross Sea shelf (modified from Collier et al., 2000). Note that maximum fluxes into sediment traps occur 3–4 months after the

summer sea-ice disappearance and are nearly coincident with the reappearance of sea ice.

C.R. Smith et al. / Deep-Sea Research II 53 (2006) 875–894878

blooms and export flux in the Antarctic areremarkably varied. Some of the processes thatmay decouple flux events from ice disappearanceor from phytoplankton blooms include the follow-ing: (1) Wind-driven dispersal of sea ice prior to itsmelting (this prevents local release of ice algae,which tend to aggregate and sink (Riebesell et al.,1991)). (2) Spatial and temporal complexity inphytoplankton bloom dynamics and advectiveprocesses on local scales (1–100 km) (Smith andSakshaug, 1990; Smith et al., 1996, 1998; Ditullioet al., 2000). (3) Variability in the occurrence,development, and die-off of nekton and zooplank-ton grazer assemblages (including krill, salps, andcopepods) that can ‘‘pelletize’’ and cause sedimenta-tion of phytoplankton blooms, or, alternatively,intensify water-column recycling (Leventer andDunbar, 1987; Bathmann et al., 1991; Loeb et al.,1997; Dunbar et al., 1998; Atkinson, 1998; Collier

et al., 2000; Zhou et al., 2004). (4) Wind-driven deepmixing, which can inhibit primary production earlyin the summer season (Dunbar et al., 1998;Ducklow et al., 2006) and cause abrupt bloomtermination with mass phytoplankton depositionlater in the summer (Gleitz et al., 1994). Thus, whilewe can conclude that intense pulses of POC flux aretransmitted to the Antarctic shelf floor, these pulsesare not always tied tightly (in space and time) tolocal sea-ice conditions or phytoplankton bloomsoverhead.

3. Question (2): Do benthic parameters (e.g., biomass

and respiration) track regional variations in water-

column processes, such as sea-ice cover and primary

production?

Most of the Antarctic shelf floor is substantiallydeeper than the bottom of the euphotic zone


(�100m), and thus sustains no in situ photosynth-esis. As a consequence, benthic food webs on theshelf must depend largely on the flux of detritalorganic matter from the pelagic zone. It thus seemsreasonable to postulate that benthic parameters onthe Antarctic shelf, such as community abundance,biomass, and oxygen consumption, will vary re-gionally (i.e. over scales of X100 km) with annualprimary production in the water column, as well aswith those factors that control annual production,such as the duration of sea-ice cover (Smith andSakshaug, 1990). Indeed, regional co-variancebetween phytoplankton production and benthiccommunity parameters has been documented forother deep seafloor habitats that depend on detritalflux from the water column, such as the abyssalequatorial Pacific (Smith et al., 1997).

At the extremes of water-column productivity,benthic parameters on the Antarctic shelf dostrongly reflect regional patterns of phytoplanktonproduction. For example, under the center of the�400m thick Ross Ice Shelf (475 km from itsseaward edge), where phytoplankton production isprevented by the absence of sunlight, Bruchhausenet al. (1979) found the abundance of macrofaunaand epibenthic megafauna to be extremely lowrelative to similar depths in the open Ross Seawhere summer phytoplankton blooms occur. Inaddition, Bruchhausen et al. (1979) saw no biotur-bation features in the muddy sediments beneath theice shelf, indicating that the abundance and activityof infaunal megabenthos were also extremely low.Similarly, macrobenthic abundance on the oligo-trophic west side of McMurdo Sound in the RossSea is an order of magnitude lower than on theeutrophic east side (Dayton and Oliver, 1977).Waters on the west side of the Sound flow north-ward from beneath the Ross Ice Shelf and havelevels of plankton biomass and productivity only10–50% of those in the eastern Sound, where watersflow southward from the relatively productive RossSea Polynya (Barry and Dayton, 1988).

With less extreme contrasts of ice duration andwater-column productivity, regional correlationsbetween water-column and shelf-floor processesbecome more difficult to detect, especially if thecomparisons are made across divergent benthichabitat types. For example, as part of the Researchon Ocean–Atmosphere Variability and EcosystemResponse in the Ross Sea (ROAVERRS) Project,Barry et al. (2003) studied the abundance andcommunity structure of epibenthic megafauna at 55

stations at depths of 270–1173m in the southwestRoss Sea and explored the strength of bentho-pelagic coupling. Their stations included a broadrange of habitat types (crest, bank, slope and basin),current regimes, and sediment organic-carbon con-tent. Barry et al. (2003) found that megabenthicabundance, diversity and faunal groupings were farmore strongly associated with benthic habitatparameters than with water-column factors suchas sea-ice duration or summer primary productivity(evaluated by CO2 drawdown in the water column),although they did find a weak association betweenprimary productivity and the numbers of trophicgroups and echinoderm classes. The habitat para-meter ‘‘depth’’ and co-varying factors such as waterflow explained the greatest amount of variance inthe abundance of a variety of taxa and trophicgroups, with a shift from suspension-feeding assem-blages at shallower depths (e.g., crests and bankswith higher flow) to deposit feeders at deeperstations (e.g., basins with lower flow). Barry et al.(2003) conclude that in their Ross Sea study region,the complex spatial distribution of banks and basinsinteracts with bottom currents to yield local zonesof erosion and deposition, obscuring the footprintof regional primary productivity. These authorsspeculate that on temporal scales of years or greater,megafaunal secondary production in the Ross Seamay be coupled to primary production in the watercolumn.

Similar control of megafaunal distributions bylocal habitat characteristics (e.g., current intensity,bottom relief, sediment type, depth, and icebergscour), rather than by regional primary productionpatterns, has been inferred from photographicstudies on the continental shelves of the Weddelland Bellingshausen-Amundsen Seas (Starmans etal., 1999; Gutt, 2000). Once again, a very broadrange of habitat types was considered (includingbanks and troughs, zones of high and low flow, andsoft and hard substrates), potentially maskingwater-column signals.

If the analysis of bentho-pelagic coupling isrestricted to a single, depositional seafloor habitattype, in particular muddy sediments, do we seestronger correlations between pelagic processes(e.g., sea-ice duration or primary productivity) andbenthic parameters? Consideration of bentho-pela-gic coupling in muddy habitats is highly relevantbecause much (perhaps most) of the Antarctic shelfbelow a depth of �200m consists of silt-claysediments (personal observations).

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1000

4000

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500

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Weddell Sea

000

100

200

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ps158

ps203

278ps196

266

275

287293

311312

313319

320

60°S

62°

64°

66°

68°

70°80°W 72° 64° 56°

Fig. 3. Stations along the western Antarctic Peninsula shelf at

depths of 100–500m where Muhlenhardt-Siegel (1988) sampled

macrofaunal biomass (see Table 1 for station depths). Data from

these stations were used in the meta-analysis of macrofaunal

biomass versus regional primary productivity. Also shown are the

Palmer LTER grid lines along the X-axis (Smith et al., 1998) for

which average primary production was evaluated for the period

1978–1986 (see text for explanation). Depth contours are in

meters.


At least two sets of data allow us to addressbentho-pelagic coupling in muddy habitats on theAntarctic shelf. Grebmeier et al. (2003) tested thehypothesis that sediment oxygen consumption,pigment concentrations, and d13C values can beused as long-term indicators of overlying primaryproduction and sea-ice dynamics. As part of theROAVERRS Project, their general study area wassimilar to that of Barry et al. (2003), encompassing a400� 600 km region of the southwest Ross Sea;however, because Grebmeier et al. (2003) workedonly at sites where plexiglass cores could be insertedinto sediments for oxygen consumption measure-ments, all their stations were dominated by silt-clay(or muddy) sediments. Over broad scales(50–100 km), Grebmeier et al. (2003) found sedi-ment oxygen consumption and chlorophyll-a (chl-a)concentrations to be highest in regions whereannual polynyas opened earliest (i.e. where sea-iceduration was shortest) and primary productionwas greatest. d13C values in surface sedimentswere also highest beneath productive polynyawaters; this pattern is expected with downwardcoupling because phytoplankton from areas ofhigh productivity in the Ross Sea are typicallyenriched in 13C relative to 12C (Villinski et al.,2000). Furthermore, concentrations of characteristicpigments (fucoxanthin and hexanoyloxyfucox-anthin, respectively) in surface sediments matchedthe general pattern of diatom-dominated produc-tion in the western part of the study area andPhaeocystis dominance in the east. Thus, Grebmeieret al. (2003) demonstrate that benthic processesand sediment parameters on the muddy Ross Seashelf reflect large-scale, multi-annual patterns ofsea-ice cover and phytoplankton production in thewater column.

A second data set allowing examination ofbentho-pelagic coupling on regional scales on themuddy Antarctic shelf comes from Muhlenhardt-Siegel’s (1988) study of macrobenthic biomass insoft sediments from 621 to 67.51S along the westernAntarctic Peninsula. Because Antarctic macro-benthos, especially larger species that dominatebiomass, appear to have generation times of yearsto decades (Arntz et al., 1994), we expect macro-benthic biomass to integrate patterns of sea-icecover, primary production and export flux overtime-scales of roughly 5–10 years. Muhlenhardt-Siegel (1988) evaluated macrofaunal biomass in1985 and 1986, using box cores or Van Veen grabs,at 13 stations on the open WAP shelf between

depths of 100–500m (i.e. from just below theeuphotic zone to the average shelf depth; Fig. 3,Table 1). To explore correlations between benthicbiomass and primary productivity, we used Smithet al.’s (1998, Fig. 3) satellite-based estimates ofnet primary production in the WAP region for theperiod 1978–1986, i.e. for the 7–8 years preced-ing Muhlenhardt–Seigel’s sampling. Specifically, wecompiled annual averages of the Smith et al. (1998)estimates of primary production along each of thePalmer Long-Term Ecological Research (LTER)grid lines (Fig. 3), and then used linear regressionto derive a general equation predicting primaryproduction as a function of distance along theWAP shelf (Fig. 4). We then used the regressionequation to estimate regional annual primaryproduction at the position of each of the stationssampled by Muhlenhardt-Siegel (1988) (Table 1).

When we compare the regional estimates ofprimary production to the log of macrobenthicbiomass from Muhlenhardt-Siegel (1988), we find ahighly significant regression relationship (Fig. 4).

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Table 1

Macrobenthic biomass for the Western Antarctic Peninsula shelf at depths of 100–500m from Muhlenhardt-Siegel (1988)

Station no. Latitude (deg. S) Depth (m) Biomass (gm�2) LTER grid X

coordinate

Annual net PP

(gCm�2 yr�1)

ps158 62.7 133 520 1000 120

ps196 62.2 485 60 1015 122

ps203 62 265 310 1025 123

266 63.2 100 280 905 111

275 63.7 180 40 800 101

278 62.7 140 200 900 111

287 63.2 230 25 800 101

293 63.2 340 20 750 97

311 65.3 420 8 305 76

312 65.9 175 12 450 68

313 66.2 270 15 390 63

319 66.6 500 40 340 58

320 67.5 420 25 320 49

‘‘LTER grid X coordinates’’ correspond to position along the Antarctic Peninsula in the X direction in the LTER grid (see Fig. 3).

‘‘Annual net primary production’’ is averaged across the continental shelf at each station position (see text for explanation).

C.R. Smith et al. / Deep-Sea Research II 53 (2006) 875–894 881

Stepwise multiple regression analysis using produc-tivity and depth as independent variables demon-strates that productivity explains the greatestpercentage of variance in biomass (52%, Fig. 4),and that the addition of depth does not significantlyimprove the regression relationship (p40:40). Weinterpret the significant relationship between pri-mary productivity and biomass to mean thatmacrobenthic biomass on the muddy westernAntarctic Peninsula shelf is controlled to a sub-stantial degree by regional primary productivity inthe water column. It is noteworthy that theregression relationship implies that a �3-foldincrease in regional primary production leads to a�10-fold increase in macrobenthic biomass. Wespeculate that this greater rate of increase in benthicbiomass may be driven by a strong positiverelationship between regional primary productionand export ratio (i.e. the proportion of primaryproduction exported to the shelf floor) over therange of production levels studied here(49–123 gCm�2 yr�1), as suggested by empirical(Lampitt and Antia, 1997) and modeling studies(e.g., Laws, 2004). Overall, we suspect that theregional imprint of water-column production onmacrobenthic biomass on the muddy WAP shelf isactually stronger than indicated in our meta-analysis because the Muhlenhardt-Siegel (1988)and Smith et al. (1998) studies were not designedto resolve the effects of bentho-pelagic coupling.

Based on the results of Grebmeier et al. (2003) andour meta-analysis of the Muhlenhardt-Siegel (1988)

data, we conclude that a number of benthicbiological parameters in muddy Antarctic shelfhabitats are likely to reflect regional patterns ofwater-column primary production. These benthicparameters are also very likely to be correlated withprocesses that control mean levels of regionalprimary production, such as annual sea-ice duration.

4. Question (3): Do major benthic processes vary in

phase with seasonal primary production and POC

flux?

As discussed earlier, Antarctic shelf ecosystemsexperience extraordinary seasonal variability, withphytoplankton production and export flux poten-tially changing by orders of magnitude betweensummer and winter (Figs. 1 and 2). Because of theintense seasonal variability in POC flux andphytoplankton availability in the water column, itwas initially expected that many benthic processeswould vary in phase with the pelagic productioncycle. Data now exist to explore seasonal variabilityin a number benthic processes on the Antarcticshelf, including sediment-community oxygen con-sumption, suspension feeding, deposit feeding, lifehistories, reproduction, and benthic recruitmentfrom the water column.

4.1. Sediment oxygen consumption

Three studies have examined seasonal patterns ofsediment-community oxygen consumption on the

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(A)

y = 0.0948x + 25.618

R2 = 0.7677

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Annual Primary Production (g C m-2 y-1)

Log

(Bio

mas

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Fig. 4. (A) Average net annual primary production for the period

1978–1986 along LTER grid lines, spaced at 100-km intervals

along the grid X-axis, running across the Western Antarctic

Peninsula shelf (see Fig. 3). Primary production values are from

(Smith et al., 1998, Fig. 2). The regression is significant at

p ¼ 0.001. (B) Log10 of macrofaunal biomass as a function of

regional primary productivity (regional productivity estimated

from the regression at top). Adding depth as an independent

variable in a stepwise mulitiple regression did not significantly

improve the fit (p40.40). Regression analyses were conducted

with SPSS Graduate Pack Version 11.5.


Antarctic shelf and all three exhibit weak season-ality compared to the pelagic production regime. At8–9m depths at Signy Island, Nedwell et al. (1993)found that while particulate-organic-matter fluxvaried �80-fold from summer to winter, sedimentcommunity oxygen consumption varied 5-fold orless. In addition, sediment-oxygen consumption wasonly weakly coupled to organic-matter flux, andexhibited much stronger inter-annual than seasonalvariability (Fig. 5). At 160m in Port Foster(Deception Island), Baldwin and Smith (2003)found similarly modest seasonal variability (2.7-fold) in sediment-community oxygen consumption(sediment trap failures prevented a direct compar-ison with POC flux in this study). Finally, in our

FOODBANCS (FOOD for Benthos on the ANt-arctic Continental Shelf) study at 500–600m on thewestern Antarctic Peninsula shelf near AnversIsland (discussed in more detail below), we foundno significant seasonal difference in sediment oxy-gen consumption for 1999–2000, even thoughimmediately overlying sediment traps recorded a�4-fold seasonal difference in POC flux whenaveraged over 3-month intervals (Smith et al., inreview). Thus, it appears that sediment-communityoxygen consumption on the Antarctic shelf showssubstantially less seasonal variability than primaryproduction in the water column, and sedimentoxygen consumption does not necessarily vary inphase with seasonal POC flux. In particular, thedampened response of sediment oxygen consump-tion to seasonal POC flux suggests that sedimentcommunity respiration on the Antarctic shelf hassubstantial ‘‘inertia’’.

4.2. Suspension feeding

Because of the extreme summer/winter contrastsin primary production and chlorophyll concentra-tions in the water column, the traditional view hasbeen that benthic suspension feeders on theAntarctic shelf should be extremely resource limitedduring the winter (Clarke, 1988; Barnes and Clarke,1995). In particular, it was expected that suspensionfeeders would experience long periods of starvation,and cease feeding (e.g., ‘‘hibernate’’) beneath wintersea ice (Clarke, 1988; Barnes and Clarke, 1995).Barnes and Clarke (1995) conducted the firstintensive seasonal study of a broad range ofsuspension feeders in the Antarctic and found thatwinter conditions (i.e. sea-ice cover and low water-column chlorophyll concentrations) persisted forabout 6 months at their Signy Island sites (2–45mwater depths). Nonetheless, many species continuedto suspension feed for all but 2–3 months inmidwinter, and at least one species (a bryozoan)fed throughout the year (Fig. 6). Barnes and Clarke(1995) suggest that many of these suspension feedersmay consume low concentrations of nanoplanktonduring much of the winter, freeing them fromcomplete reliance on the summer bloom. Theysuggest that the Antarctic winter may not be asharsh for many Antarctic benthos as once believed.

Orejas et al. (2000, 2003) built on the work ofBarnes and Clarke (1995) and suggested that theremay be two end-member suspension feeding adap-tive patterns in the Antarctic. A ‘‘fast’’ (or seasonal)

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(A)

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Fig. 5. (A) Flux of particulate organic matter into sediment traps (open circles), and sediment-community oxygen consumption (closed

circles), over time at 8–9m depth near Signy Island. (B) Sediment organic-matter content at the same station. Open circles indicate the

0–0.5 cm depth layer, and closed symbols indicate the 1–2 cm depth layer. Panels (A) and (B) modified from Nedwell et al., (1993).


feeding pattern may focus on the large phytoplank-ton of the summer bloom, with feeding andmetabolic adaptations to ingest at high rates, andto rapidly accumulate biomass and energy reservesduring summer months. Species with this ‘‘fast’’pattern, which appear to include some gorgonians(e.g., Tubularia ralphii), encrusting bryozoans, andsuspension-feeding holothurians, would then ceasefeeding for extended periods during the Antarcticwinter (Orejas et al., 2000). An alternative ‘‘slow’’(or continuous) suspension-feeding adaptive patternmay focus on smaller microplankton and resus-pended sediment particles, with adaptations to feed

and meet low metabolic costs at very low foodconcentrations throughout most (or all) of theAntarctic winter (Orejas et al., 2000). Species withthe ‘‘slow’’ pattern may not have the metabolicpotential to exploit the very high concentrationsof macrophytoplankton during summer blooms.Orejas et al. (2003) demonstrate that two species ofAntarctic octocorals can indeed feed on lowconcentrations of microplankton (e.g., ciliates,dinoflagellates, and other small phytoplankton)and on fine particles resuspended from the seafloorin a manner consistent with the ‘‘slow’’ pattern.They also postulate that the resuspension of

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Beania

Celleporella

Escharoides

Inversiula

Corbasea

Arachnopusia

Legeneschara

Himantozoum

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Hy

1991 1992 1993

droids

Fig. 6. Feeding activity (blocks) and inactivity for a range of benthic suspension feeders during 1991–1993 at 2–45m depths near Signy

Island. Dotted lines indicate periods of likely feeding, with occasional cessation due to high current velocities. Modified from Barnes and

Clarke (1995).


phytodetritus deposited during summer monthsmay contribute substantially to food availabilityfor suspension feeders over the winter (Orejas et al.,2003). In summary, it appears that the feeding ofbenthic suspension feeders may be strongly orweakly coupled to summer phytoplankton bloomson the Antarctic shelf, depending on divergentsuspension-feeding and metabolic adaptations.

4.3. Deposit feeding

Relatively few studies are available from theAntarctic shelf to evaluate seasonality in depositfeeding. The most extensive data come from studiesof the sea urchin Sterechinus neumayeri at AdelaideIsland at 67.51S along the Western AntarcticPeninsula (Brockington et al., 2001; Brockingtonand Peck, 2001). At study sites ranging in depthfrom 6 to 30m, Brockington et al. (2001) found thatS. neumayeri ceased egesting sediments, and hadempty guts, for 4–5 winter months when water-column chlorophyll concentrations were extremelylow. Chlorophyll concentrations in surface sedi-ments (0–5mm) also declined substantially duringwinter months (although total sediment organiccontent in this layer showed little seasonal varia-

tion). Metabolic rates and body-tissue (especiallygut-tissue) mass in S. neumayeri declined during thenon-feeding period, indicating that the winter was atime of starvation.

Brockington et al.’s (2001) results contrast sub-stantially with our seasonal studies of depositfeeding on the western Antarctic Peninsula shelfduring the FOODBANCS (FOOD for Benthos onthe ANtarctic Continental Shelf) project. At500–600m depths near Anvers Island (641S), Galley(2003 and Galley et al., 2005) found no evidence ofwinter cessation of feeding, or decline in energyreserves in gut and other tissues, for the depositfeeding echinoids Sterechinus antarcticus and Am-

phipneustes lorioli, or for the holothurian Protelpidia

murrayi. The holothurian Peniagone cf. Vignioni

also appeared to feed throughout the winter,although the gut tissue did exhibit a slight butsignificant seasonal variation in protein and lipidcomposition (Galley, 2003). DeMaster et al. (sub-mitted) found similar evidence of winter depositfeeding during the FOODBANCS study on thewestern Antarctic Peninsula shelf, with four speciesof surface deposit feeders and two subsurfacedeposit feeders containing recently deposited sedi-ment in their guts during all seasons sampled


(Fig. 7). Excess 234Th activity, which has a 24-dayhalf-life and is used as a tracer for sediments withhigh food value (Lauerman et al., 1997; Miller et al.,2000; Demopoulos et al., 2003), remained relativelyhigh in the guts of many of the deposit feeders evenin winter (i.e. June and October, see Fig. 7). Inaddition, 14C measurements of gut sedimentsindicated the consumption of relatively young,labile organic carbon throughout the year Purintonet al., accepted. Finally, d13C and d15N measure-ments suggested incorporation of fresh phytodetri-tus, as well as microbially reworked sedimentaryorganic matter, into deposit-feeder tissues yearround (Mincks et al., accepted). Thus, a broadsuite of deposit feeders on the western AntarcticPeninsula shelf at 500–600m depths exhibit strongevidence of (1) feeding throughout the year, and(2) ingesting high-quality material even in winter.One potentially important difference between theFOODBANCS and Brockington et al. (2001) studysites may be related to hydrodynamic regime; basedon 15 months of time-lapse photography, themuddy FOODBANCS sites have low flow velocitieswith little evidence of sediment resuspension Smithet al., in review, whereas Brockington et al.’s (2001)sites appear to be characterized by hard bottoms orcoarser sediments and more energetic flow regimes.Thus, summer-bloom phytodetritus may accumu-late and provide a sediment ‘‘food bank’’ duringmuch of the year at our FOODBANCS sites, whilesummer bloom material may be advected into

0

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h A

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114+/-6

Most Selective

Fig. 7. Excess 234Th in the gut sediments of megafaunal deposit feed

Peninsula shelf at depths of 500–600m (DeMaster et al., submitted). P

feeding holothurians; the echiuran is a burrow-dwelling surface-deposit f

feeders; and Molpadia is a head-down subsurface deposit feeder (or con

in gut sediments are the most selective feeders.

deeper waters from Brockington et al’s (2001)relatively shallow (6–30m) sites.

4.4. Life histories and reproduction

Patterns of reproduction and life history havebeen moderately studied, and widely discussed, forAntarctic macro- and megabenthos, especially forechinoderms and gastropods (Bosch and Pearse,1990; Pearse, 1994; Clarke, 1996; Poulin and Feral,1996; Galley, 2003; Galley et al., 2005). Two generalpatterns have emerged. (1) Direct and lecithotrophicdevelopment modes are overwhelmingly dominant,with planktotrophy relatively rare compared tolower latitudes (Clarke, 1996; Poulin and Feral,1996; Galley, 2003). For example, the combineddata of Poulin and Feral (1996) and Galley (2003)suggest that 43/61 (or 70%) of echinoids withknown developmental modes are brooders inAntarctica versus only 28% in Monterey Bay,California (Clarke, 1996). Benthos with directdevelopment feed at the seafloor throughout theirlife cycle, and the larvae of lecithotrophs aregenerally assumed to obtain all or most of theirnutrition from energy reserves provided with the eggby a benthic mother (but see Jaeckle and Manahan,1989, and Manahan, 1990 for exceptions). (2) Whilemany Antarctic benthos may spawn during thesummer season, many others (including species withplanktotrophic larvae) do not, leading to larvalpresence in the water column throughout the year

6

Nov. 1999 Mar. 2000Jun. 2000 Oct. 2000Feb. 2001

es Protelpidia sp.

Urchins Molpadiamusculus

0;n=8

101+/-44;n=11

40+/-28;n=8

36+/-62;n=9

Least Selective

ers collected at five different times from the western Antarctic

eniagone, Bathyplotes and Protelpidia are mobile, surface-deposit

eeder; the urchins (spatangoids) are burrowing subsurface deposit

veyor-belt feeder). Animals with the highest excess 234Th activities


(Gutt et al., 1992; Shreeve and Peck, 1995; Clarke1996; Stanwell-Smith and Clarke, 1998; Stanwell-Smith et al., 1999; Galley, 2003). Thus, mostAntarctic macro- and megabenthos studied havedevelopmental types (direct and lecithotrophic) thatrely directly on benthic energy resources and mightbe considered, at best, to be only indirectly coupledto the water column and its summer bloom. Inaddition, many species that do exploit water-column resources (i.e. those with planktotrophiclarvae) produce larvae that remain in the watercolumn at times removed from the summer bloom.This pattern suggests that the reproduction and lifehistories of many Antarctic benthos are notnecessarily tightly coupled to, or in phase with, thesummer phytoplankton bloom.

4.5. Benthic recruitment

Although the data are very sparse, recruitment ofbenthos with pelagic larvae also may be only weaklycoupled to the summer phytoplankton blooms onthe Antarctic shelf. For example, Stanwell-Smithand Barnes (1997) conducted settling-plate studiesfor 21 months at 5-25m depths at Signy Island andconcluded that the dominant settling taxa (bryozo-ans and spirorbid polychaetes) recruited essentiallycontinuously at low rates throughout the year.Similarly, McClintock et al. (1988) concluded thatthe common asteroid Odontaster validus recruitsyear round. Most recently, Bowden (2005) con-ducted the first detailed study of recruitment ofbenthos within the Antarctic Circle (67.51S, Ade-laide Island). He found a total of 39 taxa from ninephyla settling onto his plates, with dominance bybryozoans and spirorbid polychaetes. Most speciessettled throughout the year, but with a clearseasonal pattern. Perhaps unexpectedly, the peakin the number of recruiting taxa occurred in latewinter, indicating decoupling of recruitment fromthe summer phytoplankton bloom. Furthermore,recruitment of Antarctic benthos in Bowden’s studyexhibited less seasonality than for similar commu-nities in temperate latitudes, where the generalpattern is one of summer recruitment.

In summary, most benthic ecological processes onthe Antarctic shelf were initially expected to vary inphase (or in ‘‘lock-step’’) with the extraordinarilyseasonal boom/bust cycle of production in the watercolumn. In fact, many processes, including sedi-ment-community oxygen consumption, suspensionand deposit feeding, reproduction, larval develop-

ment, and recruitment, often appear to be poorlycoupled to the summer phytoplankton bloom. Whymight this be the case? The best insights are likely tobe obtained from integrative, time-series studies ofbenthic ecosystem response to seasonal and inter-annual variations in water-column production andexport flux. In the next section we discuss resultsfrom the few integrative time-series studies availablefor the Antarctic shelf.

5. Question (4): How do benthic ecosystems respond

to particular flux events or seasons?

Several benthic case studies provide time-seriesmeasurements of multiple ecosystem parametersacross seasons and years on the Antarctic shelf.We will focus on our FOODBANCS (FOOD forBenthos on the ANtarctic Continental Shelf)program, in which a broad range of parameterswere studied over a 15-month period at threestations along a transect across the western Antarc-tic Peninsula shelf south of Anvers Island (Fig. 8).These stations were chosen to be representative ofbroad areas of the mud-covered Antarctic shelf atits typical depth of 500–600m.

Sediment traps deployed �150m above theseafloor at FOODBANCS Station B indicatedstrong seasonal, and even stronger inter-annual,variability in chl-a and POC flux to the westernAntarctic Peninsula shelf floor (Fig. 9). In particu-lar, chl-a and POC flux (averaged over the 3–4month intervals of trap deployments) varied 3–4fold from summer to winter in 2000, and 4–11 foldbetween the summers of 2000 and 2001 (Fig. 9;Smith et al., in review). Time-series photographs ofthe seafloor at Station B indicated that the very highflux period during summer of 2001 was character-ized by pulsed accumulation of greenish phytode-tritus on the seafloor (Fig. 9). Nonetheless, benthicresponse to this seasonal and inter-annual varia-bility in flux was relatively muted. For example,sediment inventories of chl-a varied only 3-foldbetween summers (Fig. 10), versus an 11-fold inter-annual difference in trap chl-a flux. Other labileorganic components of the sediment, in particularenzymatically hydrolysable amino acids (EHAA),also remained high and relatively constant at all oursampling times (Mincks et al., 2005), and surfacedeposit feeders were able to ingest young, appar-ently labile organic matter throughout the year(Purinton et al., accepted; DeMaster et al., sub-mitted). In addition, sediment-community oxygen

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Fig. 8. Map of the Antarctic Peninsula region showing the locations of the primary FOODBANCS Project stations A, B and C. The

sediment trap and time-lapse camera moorings were located near station B.


consumption at Stations A through C variedroughly 2 to 3-fold between any of our five samplingtimes while POC flux varied up to 12-fold. (Hartnettet al., in revision; Thomas et al., submitted). Finally,sediment microbial biomass and macrofaunal abun-dance remained high and relatively constant acrossall our sampling times (Mincks et al., 2005; Smithet al., in review). We conclude that despite highlypulsed POC flux in summer months, labile organicmatter accumulates in western Antarctic Peninsulasediments to yield a predictable ‘‘food bank’’ fordetritivores during low-productivity winter periods.Stable isotopic analyses suggest that some of thisfood-bank material may be passing through asediment microbial loop, with microbial processingenhancing the food quality (e.g., organic-nitrogencontent) for detritivores (cf. Lovvorn et al., 2005;Mincks et al., accepted). As a consequence of thissediment food bank, many benthic processes,including sediment-community oxygen consump-tion, deposit feeding, and even bioturbation inten-sity (McClintic, 2002), exhibit substantial ‘‘inertia’’on the western Antarctic Peninsula shelf, varyingmodestly across seasons.

Given a large, metabolically active microbialcommunity in sediments at our FOODBANCSstudy sites (as indicated by high microbial biomassand sediment respiration), why do pools of labileorganic matter, such as chl-a and EHAA, persist athigh concentrations? We have hypothesized thathigh organic-matter concentrations persist becauseat very low temperatures typical of the Antarctic

shelf, microbial communities require higher sub-strate concentrations to sustain a particular level ofheterotrophic activity (see Mincks et al., 2005, fordevelopment of the hypothesis). This may result, inpart, from low temperatures causing reduced sub-strate affinities in extracellular enzymes (Nedwell,1999; Yager and Deming, 1999; Arnosti andJorgensen, 2003). Such temperature induced sub-strate limitation may then cause labile organicmatter to build up in sediments to relatively highlevels before microbial community respiration ratescan balance the sinking flux of labile POC to theseafloor (Mincks et al., 2005).

Similar muted response by benthic ecosystems topulsed POC flux has been seen in other Antarcticshelf locations. As mentioned previously, at 9mdepth at Signy Island, Nedwell et al. (1993) foundthat monthly POC flux to the seafloor variedroughly 80-fold between summer and winter, whilesediment community oxygen varied less than 6-foldover the same period (Fig. 5). Particulate organicmatter concentrations in the top 5mm of sedimentvaried even less, changing by a factor of 2 betweenseasons and years (Nedwell et al., 1993). In anotherexample, Baldwin and Smith (2003) found that, at160m depths inside the Deception Island caldera,seafloor POC flux could vary seasonally on theorder of 10-fold, while sediment-community oxygenconsumption varied seasonally less than 2-foldduring the year studied. Finally, Isla et al. (2006)document the presence of a large, persistent pool oflabile organic matter in sediments at 200–400m on

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Fig. 9. (A) Particulate organic carbon flux into sediment traps moored 150–170m above the seafloor at FOODBANCS Station B.

Means+1 s.e. are given. (B) Chl-a flux into the FOODBANCS sediment traps (left Y-axis) and phytodetritus ‘‘score’’ (right Y-axis) from

time-lapse seafloor photographs versus time after initial camera deployment on 8 December 1999. Phytodetritus scores are as follows:

1 ¼ no visible greenish phytodetritus on seafloor, 2 ¼ light dusting of phytodetritus visible, 2 ¼ moderate to heavy cover of phytodetritus

over 50–80% of the seafloor, 3 ¼ heavy phytodetritus cover over480% of the seafloor. Data fromMincks et al. (2005) and Smith et al. (in

review).


the Weddell shelf, and postulate that this providesfood of high nutritional value to detritivores duringwinter months.

We conclude that benthic ecosystem response tosummer flux pulses on the Antarctic shelf hassubstantial inertia, in part due to the presence of asediment food bank. As a consequence, manybenthic ecosystem parameters influenced by theavailability of labile organic matter, e.g., respiration

rates, levels of biomass, and rates of deposit feedingand bioturbation, may be buffered from the intenseseasonal variability in production occurring in thewater column. These parameters are likely to act as‘‘low-pass filters,’’ primarily recording longer-term(i.e. inter-annual) trends in water-column produc-tion processes as influenced, for example, byclimate-driven changes in sea-ice cover (Jacobsand Comiso, 1997; Smith et al., 2001).

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0.0

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Fig. 10. Inventory of chlorphyll-a (mg cm�2) in the top 10 cm of sediment at FOODBANCS Station B. The stippled portion of the Mar-01

bar represents the mg chl-a cm�2 in the phytodetritus layer. Means of five samples71 s.e. Modified from Mincks et al. (2005).


6. Question (5): Are there examples of upward

coupling (i.e. of seafloor processes influencing the

water column)?

Because of the great depth of the Antarcticcontinental shelf (typicallyX500m), one mightexpect upward bentho-pelagic coupling to berelatively weak. Nonetheless, there are some im-portant examples of upward coupling.

As a consequence of energetic bottom currents,complex topography, and weak density gradients, itseems quite feasible that micronutrients regeneratedat the shelf floor could be mixed up into theeuphotic zone. For example, sediments in the RossSea may be routinely resuspended to 4100m intothe water column (Collier et al., 2000). Further,Sedwick et al. (2000) argue that phytoplanktonproduction in the Ross Sea is iron-limited, and thatthe upwelling of iron-enriched waters from theseafloor enhances phytoplankton production, espe-cially that of Phaeocystis. Regeneration of micro-nutrients from the seafloor is likely to be facilitatedby the frequent occurrence of a poorly stratifiedwater column, allowing enhanced vertical mixing(Barry, 1988; Sedwick et al., 2000). Thus, phyto-plankton production in the Ross Sea and otherAntarctic regions may be substantially influenced bymicronutrient regeneration (especially of iron) inshelf sediments.

Other examples of upward coupling includepelagic or bentho-pelagic predators exploitingbenthic prey. For example, Arntz et al. (1994)reviewed data suggesting that gentoo penguins andcormorants obtain 26% and 19%, respectively, oftheir food resources from benthic amphipods. In

addition, Weddell and elephant seals feed onbenthic octopus, and nototheniid and bathydraco-nid fish consume benthic amphipods, polychaetes,ophiuroids and isopods (Arntz et al., 1994).Furthermore, Gutt (2000) describes a upwardtrophic link mediated by krill that feed at theseafloor and then are consumed by pelagic fish ormammals.

We conclude that, despite an unusually deepshelf, there is significant evidence of upward bentho-pelagic coupling in Antarctica. We suspect thatexploitation of benthic prey by pelagic predatorsmay be especially important on the Antarctic shelfduring ice-covered winter months, when water-column production is very low. The importance ofupward bentho-pelagic coupling, and its variationas a function of season and sea-ice cover, clearlymerits substantial further study on the Antarcticshelf.

7. Question (6): Will patterns of bentho-pelagic

coupling on the shelf be affected by climate change

(e.g., by warming of the Antarctic Peninsula)?

There is strong evidence on the Antarctic shelfthat the amount of annual primary production, aswell as the nature of water-column grazing andparticle export, is heavily influenced by the annualextent and duration of sea-ice cover (Smith andSakshaug, 1990; Loeb et al., 1997; Smith et al.,1998, 2001; Clarke and Harris, 2003). Climatewarming, in turn, has yielded significant reductionsin sea-ice cover along the Antarctic Peninsula(Jacobs and Comiso, 1997; Smith et al., 2001), andthere is reason to believe that this warming and


sea-ice reduction will continue (IPCC, 2001).Because benthic biomass on regional scales iscorrelated with water-column production, it is hardto imagine that climate-induced changes in sea-iceduration and primary production would not alterbentho-pelagic coupling, and in turn the structureand dynamics of benthic communities. Conceivablewarming-induced changes in bentho-pelagic cou-pling driven by shorter sea-ice duration include thefollowing: (1) a community shift among suspension-feeder to favor species with the ‘‘fast’’ (or seasonal)feeding pattern (Orejas et al., 2003) as the summerbloom season becomes longer; (2) a shift in benthicrecruitment patterns to more closely resemble thoseof the temperature zone, specifically with strongersummer peaks in recruitment (cf. Bowden, 2005);and (3) a decrease in the importance of benthic preyto pelagic predators as the water column remainshighly productive for a greater portion of the year.Nonetheless, the specific effects of climate changeon coupling are extremely difficult to predictbecause they will be influenced not only by changesin primary production, but also by poorly con-strained changes in the structure of the pelagic foodweb and the intensity of water-column recycling(Loeb et al, 1997; Ducklow et al., 2006). Suffice it tosay that changes in pelagic ecosystem structure, inparticular those modulated by long-term trends insea-ice cover (for example, a shift from krill- to salp-dominated grazer assemblages; Loeb et al., 1997),will undoubtedly influence the benthos. In fact, wesuggest that because many benthic processes act as‘‘low-pass filters’’ in the face of high-frequency (i.e.seasonal) oscillations in export flux, benthic para-meters such as biomass in various size classes ofbenthos, and labile organic-matter inventories insediments, may be especially useful indicators oflong-term trends in ecosystem dynamics in the watercolumn over the Antarctic shelf (cf. Grebmeier andBarry, 1991; Hannides and Smith, 2003).

8. Conclusions

As expected in the highly seasonal Antarcticpelagic ecosystem, large summer pulses dominatePOC flux to the Antarctic shelf floor. However, onlocal scales, these seafloor pulses often are offset intime and space from overlying plankton blooms as aconsequence of the complex suite of processescontrolling export flux.

Over regional scales (�100 km) and across allbenthic habitat types (from rocky crests to sedi-

mented basins), patterns of water-column primaryproduction are only weakly imprinted on the shelffloor. However, in the muddy habitats that aboundon the deep shelf, a variety of benthic parameters,including sediment oxygen consumption, sedimentpigment concentrations, and macrofaunal biomass,can be correlated with large-scale spatial patterns ofwater-column production and sea-ice cover. Atpresent, these regional correlations are based onlyon two studies in which benthic parameters andwater-column production were measured over thesame time interval. Clearly, if we wish to understandthe processes driving regional patterns of produc-tion, biomass and biogeochemical cycling on theAntarctic shelf floor, additional regional studies ofbentho-pelagic coupling are needed.

In contrast to initial expectations, many benthicprocesses and parameters, including sediment re-spiration, deposit feeding, reproduction, recruit-ment to hard substrata, and biomass levels, oftendo not vary in phase with seasonal patterns ofwater-column production. In fact, much of the soft-bottom benthic ecosystem is characterized bysubstantial ‘‘inertia,’’ in part due to the accumula-tion of a sediment food bank that extends theavailability of labile organic material beyond thesummer months (Mincks et al., 2005; Isla et al.,2006). Because of this inertia, many benthicprocesses may act as low-pass filters, removingseasonal ‘‘noise’’ and responding to longer-period,inter-annual trends in the flux of organic matter tothe seafloor. Thus, a number of benthic ecosystemparameters, in particular biomass levels and inven-tories of labile organic matter, potentially couldprovide useful indicators of long-term trends inexport production and pelagic ecosystem functionon the Antarctic shelf.

Major regions of the Antarctic shelf appear to beundergoing rapid climate change; in particular, theAntarctic Peninsula has sustained substantial warm-ing in the past few decades (Smith et al., 2003;Clarke and Harris, 2003). Such climate change willclearly alter pelagic ecosystems (e.g., by reducing theprevalence of sea ice) and in turn change benthicecosystems through bentho-pelagic coupling. How-ever, these climate-induced changes are extraordi-narily difficult to predict because we have limitedunderstanding of benthic ecosystem response to thenormal, often intense, inter-annual variability inprimary production and carbon flux typical of theAntarctic shelf; i.e. we know little of shelf commu-nity resistance and resilience in the face of natural


perturbations. The presence of a substantial foodbank in Antarctic shelf sediments (Mincks et al.,2005) is likely to confer relatively high resistance inbenthic foodwebs to short-term variations inprimary production and export flux. However, theresilience of Antarctic shelf ecosystems in the face ofclimate warming (i.e. their speed of recovery oncesubstantially perturbed by climate change) could bevery low, especially if warming reduces the size ofthe benthic food bank by raising bottom watertemperatures (Mincks et al., 2005) or by increasingthe efficiency of water-column recycling.

Climate varies substantially with latitude alongthe Antarctic shelf, offering exciting opportunitiesto explore the effects of climate change on bentho-pelagic coupling and benthic ecosystem function.For example, annual sea-ice duration ranges fromroughly 2–3 months at 641S to �10 months at 691Salong the western Antarctic Peninsula (Jacobs andComiso, 1997). Well-designed studies of benthicecosystem responses to both (1) inter-annual varia-bility in export flux, and (2) latitudinal gradients inpelagic ecosystem function are urgently needed toelucidate the impending effects of climate change onbentho-pelagic coupling in the Antarctic.

Acknowledgments

We sincerely appreciate the efforts of numerousFOODBANCS participants who made our work inAntarctic possible, especially A. Glover, P. Sumida,C. Thomas, M. McClintic, T. Ferrero, N. Deben-ham, S. Suhr, E. Galley, and R. Jeffreys. We thankD. Karl for access to unpublished sediment-trapdata from the Palmer LTER Program. We alsothank A. Clarke for inviting this paper, and formaking the EASIZ Final Symposium in Korcula,Croatia, an outstanding success. The careful effortsof four anonymous reviewers substantially im-proved this paper. The FOODBANCS Project andtravel to the EASIZ Symposium was supported byGrants from the National Science Foundation,Office of Polar Programs to C.R.S. and D.J.D.This is contribution number 6798 from SOEST,University of Hawaii at Manoa.

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