Polar Biol (2007) 30:1323–1329

DOI 10.1007/s00300-007-0293-z

ORIGINAL PAPER

Mega-epibenthic diversity oV Terre Adélie (Antarctica) in relation to disturbance

Julian Gutt · Philippe Koubbi · Marc Eléaume

Received: 3 November 2006 / Revised: 2 April 2007 / Accepted: 9 April 2007 / Published online: 24 May 2007© Springer-Verlag 2007

Abstract Mega-benthic assemblages have been analyzedoV Terre Adélie (East Antarctica) between 20 and 110 mdepth by seabed videography. The study area is dominatedby high abundances of sessile suspension feeders, however,sponges are rare at this depth. There are hints and evidencethat diVerent levels of disturbance and biological dynamicsaVect these assemblages. Biodiversity results are inter-preted with the background of an applicability of the inter-mediate-disturbance hypothesis (IDH).

Keywords Intermediate-disturbance hypothesis · Sea-bed video · Assemblages · Iceberg scouring · Suspension feeders

Introduction

Antarctic epibenthic assemblages below the littoral zoneseem to exhibit highest between-site heterogeneity in

shallow water (Gutt 2007). Reason for this is a complextemporal and spatial variability in environmental condi-tions including diVerent kinds of disturbance (Clarke andArntz 2006; Thrush et al. 2006; Barnes and Conlan 2007).However, similar environmental conditions around thecontinent can also support similar assemblages at a localand even at a regional scale. The aim of the study was todescribe mega-benthic assemblages oV Terre Adéliebetween 20 and 110 m water depth based on abundanttaxa or life modes. As a consequence these could be clas-siWed at the level of data interpretation based on a recentreview of the Antarctic macrobenthic shelf communities(Gutt 2007) including results from previous studies in thearea (Arnaud 1965, 1974; Beaman and Harris 2005). Thefaunistic compositions were to be explained by local andregional environmental dynamics such as iceberg distur-bance or due to the proximity to the Astrolabe Glacier.This interpretation centres on the Intermediate-Distur-bance Hypothesis (IDH) primarily not in order to conWrmits generality or reject it for this part of the Antarctic ben-thos but because the IDH provides a useful tool for a bet-ter understanding of the relationship between the faunaand its environment. The ichthyofauna has been investi-gated in this area in the course of the ICOTA project (Ich-tyologie Côtière en Terre Adélie; Koubbi et al. 1997;Hureau et al. 2000) since 1996. In 2006, seabed video wasused to correlate the Wsh fauna and benthic assemblagesas an overall and Wnal objective of the project. Thismethod provides a quantitative overview of the dominantgroups of mega-benthic organisms even in areas with hardsubstrata, and relatively large areas can be covered with ahigh spatial resolution. Consequently the results cancontribute to a general concept of Antarctic marinebioregionalization.

J. Gutt (&)Alfred Wegener Institute for Polar and Marine Research, 27568 Bremerhaven, Columbusstr, Germanye-mail: julian.gutt@awi.de

P. KoubbiLaboratoire d’Ichtyoécologie Marine, Université du Littoral Côte d’Opale, Quai Masset, Bassin Napoléon, B.P. 120, 62327 Boulogne-sur-Mer cedex, Francee-mail: koubbi@univ-littoral.fr

M. EléaumeDépartement Milieux et Peuplements Aquatiques, UMR 5178 Biologie des Organismes Marins et Ecosystèmes, Muséum national d’Histoire naturelle, CP 51. 57, rue Cuvier, 75005 Paris, Francee-mail: eleaume@mnhn.fr

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Material and methods

Investigations have been carried out in January–February2006 in Baie Pierre Lejay covering an area of 18 £ 25 kmoV Terre Adélie at 66°40�S, 140°E (Fig. 1). Sea-Xoortopography is characterised by the upper slope of a north-east to southwest orientated inner-shelf depression(·550 m) in the west and a shallower plateau in front of thecontinental ice-cliVs in the south and the Astrolabe Glacierwhere a inner-shelf depression of >1,000 m depth exists.An oV-shore plateau of approx. 100 m depth is situated inthe north-west and north. Islands and islets of the Pointe-Géologie archipelago form the eastern and western bound-aries of the bay at depths of 10–70 m. Usually only smallicebergs are present in the bay due to shallow depths. Largeicebergs drift in front of the Astrolabe Glacier and at themargins of the investigation area where depths exceed100 m. Sea-ice begins to form in mid March but can breakout until July due to strong and frequent katabatic winds. Inspring it usually breaks out by late November (Loots et al.2007).

The epibenthic fauna was surveyed by ROV-transects(Achille M4, Comex), at 14 stations (Fig. 1) using a high-resolution camera (Sony HVRA1E). Calculated from GPSpositions at approx. 2 min intervals, a standardised transectlength of approx. 200 m, was selected for each station. Atstation 14, 15, and 17 two pseudoreplicates were analysed.Each transect was split into 10 m intervals (§4 m). Onlytaxa with >2 specimens of >2 cm in approx. one-third of acomplete transect (Table 1) were included in the faunisticanalysis. This ensured that only a low percentage of visu-ally hidden specimens falling into this category were

neglected with the exception of the macroalgal-dominatedassemblage mentioned below. Taxa were registered to beeither of high or low dominance (relative values: 3 and 1,respectively) within each 10 m interval. In addition, sea-Xoor cover of all these taxa was estimated for each intervalusing the following classes and their means: 0–1%: value0.005; 1–5%: value 0.03; 5–33%: value 0.14; 33–67%:value 0.5; 67–100%: value 0.84. Absolute abundance prox-ies for each taxon and each 10 m interval were calculatedby multiplying the relative abundance by the mean of thesea-Xoor cover and averaged for the entire transect. Themysids were registered only with relative value = 1 ifn ¸ 10 m-2 for ¸5 m transect length. Absolute abundanceproxies were standardized to relative abundance proxies forbetween-cluster comparison. Based on absolute abundanceproxies a community and diversity analysis was performedusing PRIMER software: Bray-Curtis similarities, Clusteranalysis (average linkage) for stations and taxa multi-dimensional scaling (MDS), Hill 2 (N2 = reciprocal Simp-son’s) diversity index, dominance-plots to assess betadiversity, and SIMPER to identify key taxa comparingabundances within one cluster with that of all other stations(average contribution to the overall dissimilarity/standarddeviation of the Bray-Curtis similarities between all pairsof samples for this species = Diss/SD) excluding the bulkgroups Porifera spp. and compound ascidians.

Results

The MDS-plot shows four station groups plus the isolatedstn 9 according to their taxa inventory if the result of a cluster

Fig. 1 Area of investigation with classiWcation of mega-bentic fauna according to cluster analysis. Black areas indicate rocks, spotted areas ice/snow-covered continent and islands

0060040030020010552

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Polar Biol (2007) 30:1323–1329 1325

analysis at 40% similarity is superimposed (Fig. 2,Table 2). For the faunistic composition at a coarse taxo-nomic level see Fig. 3.

In group M macroalgae were most abundant. Here, themega-zoobenthos might be underrepresented in the data setdue to the method used and, as a consequence, biodiversitywas lowest (Figs. 4, 5). However, even in areas withoutmacroalgae only a poor fauna was visible.

In cluster H diversity sharply increased with increasingdepth between 30 and 64 m not only in terms of equitabilitybut also in terms of species numbers and a combination ofboth (Figs. 4, 5). Throughout there were no really dominantspecies. Cnidarians and dendrochirote holothurians formedthe dominant ecological guild of Wlter feeders (Fig. 3).The only reasonable key taxon was the half-infaunal

Table 1 List of taxa

Most species identiWcation based on the species list of Arnaud (1974)

Macroalgae5 Himantothallus grandifolius

A2: Filamentous shape

Porifera Porifera spp: incl. few hexactinellid (glass-) sponges and demosponge e.g. Cinachyra barbata

P1: Cone-shaped, light beige, mainly on hard substratum

Isodictya antarctica

Homaxinella balfourensis

P5: Tubes with one osculum each on top, several tubes connected at their basis, surface like Mycale, yellow

Hydrozoa Oswaldella antarctica

Gorgonaria Primnoella spp., two “morpho-types” or species, one with more the other with less obvious side branches

Touarella/Dasystenella

Ascolepis cf spinosa; two types: not branching at the top 2/3 of the colony or branching everywhere, orange

Varia EL: Xat grey leave-like structure, approx. 1 cm thick, ·20 cm in diameter. Most likely a sponge

Bryozoa Cellarinella sp. 1, Fan-shaped beige/orange

B2: Bushy, moss-like; branches only visible in close-ups; white/beige/grey; probably several species

cf Cellarinella sp. 2, Yellow branches being clearly visible, probably several species

Polychaeta Perkinsiana antarctica

P9: Grey bent tubes more or less lying on the sediment; no tentacles visible, only at stn 9

Bivalvia Laternula elliptica

Mysidacea Antarctomysis maxima or Mysidetes posthon

Isopoda Antarcturus furcatus or Chaetarcturus franklini

Holothuroidea H1: Posterior 2/3 of body in, rest incl. tentacle crown above sediment, white; includes Ekmocucumis stein-eni, a life mode rather than a systematic taxon

H2: Epibiotic including completely white and small brown species (such as Ekmocucumis steineni)

H3: Living on the sediment or epibiotic, grey-brown including Psolus charcoti and Ekmocucumis steineni

Echinoidea, Regularia Sterechinus neumayeri

Echinoidea, Irregularia Abatus cavernosus and/or nimrodi; dark red to dark green

Ophiuroidea All ophiuroids

Ascidiacea Compound ascidians

Cf juveniles of Synoicum adareanum and/or georgianum. At stn 17 this taxon includes intermediate sized colonies

Adults of Synoicum adareanum and/or georgianum

Distaplia cylindrica

S4: Like Distaplia cylindrica but orange, never 1 m long

Fig. 2 MDS-Plot of stations with classiWcation from cluster analysissuperimposed

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1326 Polar Biol (2007) 30:1323–1329

holothurian H1 (1.33 Diss/SD). The sponge Homaxinellabalfourensis was most abundant only at stn 10. Small scalebottom topography and faunistic composition at stns 11 and14A showed discrete irregularities (Fig. 6).

Cluster D was formed by stations being 62–109 m deepat the edge of the innershelf depression and oV-shore withalpha- and gamma-diversities remaining on a high level(Figs. 4, 5). Nevertheless two most abundant taxa wereworthwile to be identiWed: adults of Synoicum adareanumand/or georgianum (1.32 Diss/SD) and Cellarinella sp. 1(1.03 Diss/SD).

Stn 9 was clearly dominated by only two taxa: juveniles ofSynoicum adareanum and/or georgianum and polychaeta P9; itwas situated in front of the ice-cliVs of the Astrolabe Glacier.

At intermediate water depths (41–90 m) cluster O com-bined two stations in the grounding area of icebergs calvingfrom the Astrolabe Glacier and the most oV-shore station atthe inner-shelf depression. Alpha diversity was low; themost dominant and characteristic species were the hydro-zoan Oswaldella antarctica (3.74 Diss/SD, followed by thebryozoan cf Cellarinella sp. 2 (1.28 Diss/SD) and the epibi-otic holothurians H2 (1.92 Diss/SD).

Table 2 Absolute abundance proxies, stations and taxa classiWed according to cluster analysis

Stations

Taxa 19 7 12 15B 8 17A 16 18 15A 6 17B 14A 10 11 9 14B 13

Hydrozoa Oswaldella antarctica 42.3 31.2 31.1 0 6.3 1.0 0 4.2 9.8 16.1 9.2 4.3 5.0 2.3 0 0.0 4.0

algae Himantothallus grandifolius 0 0 0 0 0 0 0 0 0 0 1.5 0.1 0.5 0.0 0 27.5 19.8

Ascidiacea Synoicum adareanum and/or georgianum (adult)

15.4 3.4 0.5 24.2 8.3 13.2 8.3 3.9 12.7 0.8 0.6 0 0 0.7 0 0 0

Polychaeta P9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 15.7 0 0

Bryozoa Cellarinella sp. 2 4.7 0 0 1.1 0 22.9 9.0 15.6 3.5 3.8 0 0 0 0 0 0 0

Bryozoa B2 8.6 30.7 1.0 3.6 1.9 7.7 11.3 2.5 1.6 12.2 1.8 0 0 0 2.1 0 0

Polychaeta Perkinsiana antarctica 21.2 9.4 11.2 8.0 3.1 11.3 8.3 9.0 12.5 10.5 3.8 4.5 4.5 0.9 2.9 1.4 5.2

Gorgonaria Primnoella spp. 18.1 5.2 2.0 8.7 6.3 6.2 6.3 8.2 10.3 11.1 5.8 8.5 2.7 1.7 0 0 0

Echinoidea Abatus cavernosus and/or nimrodi

3.5 1.3 0.5 9.2 6.5 8.2 6.8 5.1 8.8 5.6 2.8 2.9 3.5 1.6 0 0 0

Ascidiacea Compound ascicians 15.3 7.2 0.5 6.7 4.6 10.0 7.3 6.0 9.5 9.6 2.9 3.3 0 1.8 1.8 0 0

Holothuroidea H1 0 0.5 6.2 1.0 0 4.0 0.5 0.2 1.3 0.5 1.3 4.9 8.9 2.1 0 0 5.0

Ophiuroidea 3.5 1.3 3.2 9.2 1.1 1.6 0.5 0.2 7.0 0.6 1.1 4.5 2.4 2.0 2.8 0.5 1.1

Holothuroidea H2 16.5 14.4 5.7 5.2 1.1 3.7 1.8 3.2 3.8 5.1 0.6 6.4 0.1 2.3 0 0 0.5

Holothuroidea H3 3.9 6.4 5.5 0.5 0 6.9 5.3 7.7 2.3 0.1 0.5 3.5 0.6 2.1 0 0.2 1.3

Bryozoa Cellarinella sp. 2 16.1 26.2 3.5 3.6 3.2 4.0 3.0 4.9 8.3 0.5 1.0 0 0 0 0 0 0

Gorgonaria Ascolepis cf spinosa 5.5 0 0 2.3 4.6 4.2 4.1 12.3 7.5 7.3 1.4 0 0 0 0 0 0

Gorgonaria Touarella/Dasystenella 13.6 1.3 0 3.0 4.8 8.2 7.8 6.7 1.5 1.0 0 0.5 0 0.1 0 0 0

varia most likely a sponge (EL) 14.8 1.3 0 9.2 6.0 5.0 5.3 3.2 5.3 3.6 2.4 2.8 0 0 0 0 0

Ascidiacea S4 8.6 1.7 1.0 3.7 3.1 6.8 3.8 4.4 2.5 2.5 4.9 2.9 0 0.7 0 0 0

Ascidiacea cf Synoicum adareanum and/or georgianum (juvenile)

7.0 0 0.5 8.2 3.1 12.1 1.0 2.0 0 0.5 2.1 0 0 0.8 7.5 0 0

Crustacea:Isopoda Antarcturus furcatus or Chaetarcturus franklini

0 0 14.9 0 0.5 1.3 0.0 1.3 3.5 0.5 0.0 0 0 <0.1 0 0 0

Echinoidea Sterechinus neumayeri 0 0 4.7 0 0 0 0 0 0 0 0 0 0 0.1 0 0 3.0

Porifera P1 1.7 0 0 0 0 0.8 0.5 0.8 1.0 0 2.9 0 0 0 0 0 0

macroalgae A2 0 0 2.3 3.2 1.5 0 0 0 3.0 0.5 2.1 0.6 1.6 0.4 0 3.0 0.1

Bivalvia Laternula elliptica 0 0 0.5 0.5 0 0 0 0 0.5 0 2.7 0.1 2.8 0.9 1.6 0 <0.1

Porifera Isodictya antarctica 0 0 1.8 0 0 0 0 0 0 0 0 0 4.2 0 0 0 0

Porifera Homaxinella balfourensis 0 3.4 0.5 0 0.1 1.5 0 0 1.5 0 0 1.0 4.3 1.7 0 0 0

Porifera Porifera spp., incl. Cinachyra barbata and hexacinellida

6.4 2.5 10.4 2.2 3.3 6.5 3.0 1.8 2.0 0.5 1.3 0.8 3.1 0.1 0 0 0.5

Crustacea: Mysidacea

Antarctomysis maxima or Mysidetes posthon

1.3 0 0.5 5.6 4.1 3.1 5.8 1.7 3.0 0 0.1 0 0 1.4 0 0 0

Porifera P5, surface like Mycale 1.7 3.9 4.0 5.7 1.6 4.5 3.0 5.9 0.5 0.5 0 0 0 0 0 0 0

Ascidiacea Distaplia cylindrica 1.3 0 0 3.7 3.2 2.5 0 1.0 0.6 1.8 0 0.6 0 0.3 1.0 0 0

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Discussion

In general the species composition oV Terre Adélie is inaccordance with part of the circumpolar macrobenthic com-munities classiWed by Gutt (2007). Due to the low abun-dance of sponges it can be attributed to the “Filter feederassemblage dominated by others apart from sponges” alsofound, e.g. in the eastern Weddell Sea at comparabledepths. Considerable abundances of predators as describedfor McMurdo Sound by Dayton et al. (1994) and Thrushet al. (2006) have not been observed. A rich infauna repre-sented by bivalves and holothurians inhabiting soft sedi-ments occurred only in small patches. Also a vagrant faunaas described for the deeper parts of the easterly adjacent

George V Shelf by Beaman and Harris (2005), e.g. domi-nated by sea-urchins and the partly hyperbenthic mysids donot contribute to form a signiWcantly diVerent community.They become abundant in gaps surrounded by sessile sus-pension feeders, which serve locally as substratum for epi-bionts, mainly holothurians, compound ascidians andantarcturid crustaceans. For general similarity betweenclusters at a higher systematic level see Fig. 3. Local envi-ronmental variability might also be the reason for theabsence of the clam Adamussium colbecki, which wasfound by Arnaud (1965, reviewed by Schiaparelli and Linse2006) in high abundances. Environmental stability due toalmost permanent sea-ice cover might support the domi-nance of this and other species, whereas at the moredynamic sites investigated in this study diversity can behigher due to intermediate levels of disturbance. In generalour faunistic results are also partly in accordance with thestudy of Beaman and Harris (2005) covering a larger areaand depth range and using more environmental but biologi-cally coarser parameters. The observed distribution of mac-roalgae between 21 and 35 m depth follows the generalpattern according to light limitation in the Antarctic(Wiencke et al. 2006). Previous studies in this area showedtheir lower limit on hard and sandy bottoms to be at 45 m(Mawson 1940; Beaman and Harris 2005).

The main conceptual tool to explain regional biodiversitypatterns found in this study is the intermediate-disturbancehypothesis (IDH, Huston 1979). It predicts in a dynamicenvironment low diversity if species are eliminated byintense disturbance and, as a consequence, only few survi-vors or pioneers shape the assemblage. It also predicts lowdiversity in a stable environment if species get locally

Fig. 3 Relative composition of higher systematic units for each clus-ter based on absolute abundance proxies

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Fig. 4 Dominance-plots based on abundance proxies within clusters

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Fig. 5 Hill 2 (N2) diversity at the alpha level versus depth. For clusterssee Fig 2. Letters indicate concepts of diversity “behaviour” accordingto the IDH. A increasing diversity with depth reaches an optimum at»70 m due to assumed decline in disturbance; B increasing diversityreaches a maximum but declines with increasing depth, since at ap-prox. 50 m depth disturbance is supposed to represent an intermediatelevel; C diversity increases continuously with depth due to increasingenvironmental stability. For symbols see Fig. 3

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1328 Polar Biol (2007) 30:1323–1329

extinct due to competitive displacement (Gutt 2006). Atintermediate levels of disturbance and competition it isassumed that a broad variety of species coexist includingpioneers and species that are superior in competition, butnone of them dominates the assemblage. As a consequence,in such a situation diversity reaches an optimum.

In the shallow cluster M macroalgal growth can be con-sidered either as an intense disturbance impact to the rest ofthe benthic community or macroalgae can be considered asorganisms superior in competition in a non-disturbed situa-tion. Which interpretation ever is applied, both processeslead to a decrease in diversity according to the IDH.

The increase of diversity in cluster H with increasingwater depth at approx. 50 m agrees with Wndings of Barnes(1999) at Signy Island. Here, Wne-scale irregularities in thebottom topography and the high abundance of Homaxinellabeing characteristic for areas aVected by anchor ice(Dayton 1989), glaciers (Dawber and Powell 1997) andicebergs (Gutt and Piepenburg 2003) provide evidence foriceberg disturbance (Fig. 6). Obviously, however, a Wnetuned equilibrium between such physical disturbance and alow level of competition in an otherwise relatively stableenvironment leads almost to a diversity maximum at boththe within and between habitat levels (Figs. 4 , 5, scenarioA and B). This agrees with our own observations above

sea-level of the presence of grounded and Xoating smallicebergs in this area.

In the deeper cluster D alpha- and gamma-diversitiesremain on a high level (Figs. 4 , 5) despite the dominanceof two taxa. There is only one hint for spatially limitediceberg disturbance in this cluster at stn 18 being toosmall to aVect the entire diversity pattern considerably.The situation at an oV-shore slope in combination withgreater water depth compared to cluster H being locatedon a plateau seems to reduce risks of iceberg disturbance.Here a high complexity and dynamics of the total of allrelevant ecological conditions obviously allowed a rela-tively high number of species to reach intermediate abun-dances (Fig. 5, scenario A). This is similar to deeperassemblages of Wlter feeders in the Weddell Sea where, incontrast to the IDH, environmental stability does not leadto a reduced diversity (Gutt and Piepenburg 2003). AlsoArnaud (1965, 1974) registered in this depth zone highestspecies richness including a majority of sessile suspen-sion feeders.

At such depth, however, diversity can also be lowerespecially at station 9 where the sediment was the mostmuddy. It was only here that juveniles of Synoicum adar-eanum and/or georgianum did not co-occur with theiradults. The polychaete P9 was found exclusively at this

Fig. 6 Iceberg disturbance. Video transects with most clear hints for discrete gaps due to iceberg scouring (arrows) not only based on the fauna but also on Wne-scale irregularities in the bottom topography. Low abundances in other parts of the transects to be explained by other unknown ecological processes. Taxa according to the column of patterns (right of stn 11) from top to bottom: Synoicum adareanum and/or georgianum juvenile, Synoicum adareanum and/or georgianum adult, compound ascidians, ophiuroids, Abatus cavernosus and/or nimrodi, Psolus charcoti and/or Ekmocucumis steineni (H3), epibiotic holothurian (H2), half-infaunal holothurian (H1), Antarctomysis maxima or Mysidetes posthon, Laternula elliptica, Perkinsiana antarctica, Primnoella, Oswaldella antarctica, Homaxinella balfourensis

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Polar Biol (2007) 30:1323–1329 1329

station in densest patches. Arnaud also described poly-chaetes as a dominant faunistic element in generally poor“infra- and circalittoral” assemblages, however, this wasbased on species numbers rather than quantitative domi-nance patterns. All these are hints for a dynamic biologicalsystem with fast growth and/or successful recruitment dueto the immediate proximity to the glacier. There are alsolocal bottom topography peculiarities that support thisinterpretation. In general the shore line at station 9 is morestable than the eastern front of the glacier but small ice-bergs can be observed.

At the oV-shore stations of cluster O medium to largeicebergs were observed. The low alpha diversity can beexplained -as for the macroalgae assemblage- either by adisturbance level being higher than in the more diversecluster D (Fig. 5, scenario C) together with station 9 or bycompetitive displacement (Fig. 5, scenario B) in a stableenvironment. Evidence for the Wrst explanation is missingfor cluster O, which might be due to the low number of sta-tions but not for station 9. Competition might play animportant role since this benthic system must be consideredto have a fast development compared to those where slowgrowing demosponges or hexactinellid sponges are moreabundant as regionally in the Weddell and Ross Seas. Thedominant and characteristic taxa Oswaldella and Cellari-nella are generally known to be fast growing. It should beemphasized that the reduced diversity with depth in thiscluster was a matter of evenness rather than species rich-ness, which might be either due to the method or sinceevenness reacts more sensitively to biological interactionsbefore species are outcompeted. It can be speculated thatbelow this zone or area diversity will increase again asfound e.g. in the Weddell Sea (Starmans and Gutt 2002)and perform a bimodal diversity curve (Johst and Huth2005). With the exception of stn 9 hints for generally diVer-ent physical settings aVecting a high diversity in one andlow diversity in the other deeper cluster are missing.

We can Wnally conclude that physical parameters suchas proximity to glacier, iceberg scouring, light, andcurrent regime shape a suspension feeder dominatedmegabenthic community oV Terre Adélie between 20 and110 m depth with cnidarians, ascidians, and polychaetesbeing the most dominant animal groups. In addition,heterogeneity in biodiversity at smaller spatial scales(tens to hundreds of m) with eVects on larger scales isaVected by biological processes such as competition andrecolonization.

Acknowledgments ICOTA project funded by IPEV. Data analysisand publication funded by Université Littoral Côte d’Opale, by guestprofessorship of J. Gutt. Thanks to Département du Finistère for pro-viding the ROV and to Océanopolis for the camera, to ROV pilots A.Pottier and D. Fleury and the electronic staV of Dumont d’Urville sta-tion for their support.

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