Macro-and megabenthic assemblages in the bathyal and abyssal Weddell Sea (Southern Ocean)

Deep-Sea Research II 54 (2007) 1848–1863

Macro- and megabenthic assemblages in the bathyal and abyssalWeddell Sea (Southern Ocean)

Katrin Linsea,!, Angelika Brandtb, Jens M. Bohnc, Bruno Danisd,Claude De Broyerd, Brigitte Ebbee, Vincent Heterierf,

Dorte Janusseng, Pablo J. Lopez Gonzalezh, Myriam Schullerf,Enrico Schwabec, Michael R.A. Thomsoni

aBritish Antarctic Survey, Natural Environmental Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UKbZoologisches Institut und Museum, Universitat Hamburg, Martin-Luther-King Platz 3, D-20147 Hamburg, Germany

cZoologische Staatssammlung Munchen, Munchhausenstr. 21, D-81247 Munchen, GermanydRoyal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000 Bruxelles, Belgium

eForschungsinstitut Senckenberg, DZMB-CeDAMar, c/o Forschungsmuseum Konig, Adenauerallee 160, D-53113 Bonn, GermanyfUniversite Libre de Bruxelles, Laboratoire de Biologie Marine, CP 160/15, 50 av. F.D. Roosevelt, B-1050 Bruxelles, Belgium

gForschungsinstitut und Naturmuseum Senckenberg, Sektion Marine Evertebraten I, Senckenberganlage 25,D-60325 Frankfurt am Main, Germany

hDepartamento de Fisiologıa y Zoologıa, Facultad de Biologıa, Universidad de Sevilla, Avda. Reina Mercedes 6, E-41012 Sevilla, SpainiSchool of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK

Accepted 6 July 2007Available online 3 August 2007

Abstract

The assemblages inhabiting the continental shelf around Antarctica are known to be very patchy, in large part due todeep iceberg impacts. The present study shows that richness and abundance of much deeper benthos, at slope and abyssaldepths, also vary greatly in the Southern and South Atlantic oceans. On the ANDEEP III expedition, we deployed 16Agassiz trawls to sample the zoobenthos at depths from 1055 to 4930m across the northern Weddell Sea and two SouthAtlantic basins. A total of 5933 specimens, belonging to 44 higher taxonomic groups, were collected. Overall the mostfrequent taxa were Ophiuroidea, Bivalvia, Polychaeta and Asteroidea, and the most abundant taxa were Malacostraca,Polychaeta and Bivalvia. Species richness per station varied from 6 to 148. The taxonomic composition of assemblages,based on relative taxon richness, varied considerably between sites but showed no relation to depth. The former three mostabundant taxa accounted for 10–30% each of all taxa present. Standardised abundances based on trawl catches variedbetween 1 and 252 individuals per 1000m2. Abundance significantly decreased with increasing depth, and assemblagesshowed high patchiness in their distribution. Cluster analysis based on relative abundance showed changes of communitystructure that were not linked to depth, area, sediment grain size or temperature. Generally abundances of zoobenthos inthe abyssal Weddell Sea are lower than shelf abundances by several orders of magnitude.r 2007 Elsevier Ltd. All rights reserved.

Keywords: Macrofauna; Megafauna; Benthos; Deep-sea; Antarctica; South Atlantic

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www.elsevier.com/locate/dsr2

0967-0645/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.dsr2.2007.07.011

!Corresponding author. Tel.: +44 1223 221 631; fax: +44 1223 221259.E-mail address: [email protected] (K. Linse).

1. Introduction

In the last three decades, since the discoveries ofabyssal hydrothermal vents and manganese no-dules, scientific and commercial interest in studyingthe global deep oceans has increased greatly (e.g.,Bluhm, 1994; Decraemer and Gourbault, 1997;Lambshead et al., 2002; Tyler et al., 2002; VanDover et al., 2003; Van Dover and Lutz, 2004). Sitesin the deep North Atlantic and Pacific oceans haveespecially become the focus of long-term projects,and what started as descriptive research there hasmoved into process-orientated investigations (Bettet al., 2001; Billett et al., 2001; Narayanaswamyet al., 2005). Much less is known about the deep-seaassemblages of the Arctic, Indo-Pacific and South-ern oceans (Bluhm et al., 2005; Brandt et al., 2004a;Ingole, 2003; Kroncke, 1998; Wlodarska-Kowalczuket al., 2004). About half the world’s surface isabyssal yet only tiny areas have been visited and weknow very little of the biodiversity and abundanceof animals there (Rex et al., 2006). One of the least-known abyssal areas surrounds Antarctica, the deepSouthern Ocean.

For more than a century, deep-water sampleshave occasionally been taken in the SouthernOcean. Most of these studies, such as the Russianexpeditions with R.V.s Ob, Akademik Kurchatovand Dmitriy Mendeleev (Malyutina, 2004 andreferences therein) and American expeditions withUSNS Eltanin and R.V. Hero (Dell, 1990), con-centrated on describing and discovering species.Assessments of macro- or megafaunal abundances,community structure or richness levels were see-mingly not considered. The recent ANDEEPexpeditions to the Antarctic and South Atlantichave greatly increased our knowledge of faunalabundances in the deep sea (Brandt et al., 2004b).During the ANDEEP I and II expeditions, benthicfauna was sampled in bathyal and abyssal depths(1121–6348m) of the Shackleton Fracture Zone, thenorthern Weddell Sea Basin, and the SouthSandwich Islands. However, most studies have beenrestricted to specific taxonomic groups (Brandtet al., 2004b; Cornelius and Gooday, 2004; Linse,2004) or meiofauna (Gutzmann et al., 2004;Vanhove et al., 2004) and macrofauna (Blake andNarayanaswamy, 2004). Information about deepmegabenthic assemblages, communities and abun-dances across taxa is still scarce (Brandt, 2005). Incontrast to the nearly unknown deep sea, theAntarctic shelf fauna and its community composi-

tion are much better known (e.g., Arnaud et al.,1998; Arntz et al., 1994, 2005; Dayton et al., 1994;Ramos, 1999; VoX, 1988). To date most studies ofabundance in shelf communities and assemblageshave focussed on gaining quantitative assessmentsof soft-bottom habitats (Gambi and Bussotti, 1999;Gerdes et al., 1992, 2003; Lovell and Tregi, 2003;Piepenburg et al., 2002; Saiz-Salinas and Ramos,1999; Saiz-Salinas et al., 1997). Macrobenthiccommunity abundance assessments using semi-quantitative methods (dredges, sledges and trawls)have been undertaken by VoX (1988) in the WeddellSea, by Arnaud et al. (1998) in the South ShetlandIslands, and by Rehm et al. (2006) in the Ross Sea.Barry et al. (2003) analysed the shelf and upperslope assemblages in the Ross Sea by using towedcamera footage. Linse et al. (2002) investigated thesuprabenthic fauna in the Weddell Sea and theSouth Shetland Islands. On many Antarctic benthicexpeditions, the relative abundances of macro- andmegabenthic taxa were assessed on variablepoint classifications from absent to very abundant(Allcock et al., 2003; Arnaud et al., 1998; Arntz andGutt, 1997, 1999; Arntz and Brey, 2003; Arntz et al.,2006) but no numerical data were collected.

During ANDEEP III, the faunal assemblagescollected by Agassiz trawl were assessed by highertaxon classification and numerical data takenallowing comparison with faunal assemblages fromthe Antarctic shelf. This paper is the first attempt todescribe deep-sea mega- and macrobenthic assem-blages of the Weddell Sea and their abundances.

2. Material and methods

2.1. Study area

Four study regions were selected, but the mainfocus was on the Powell Basin and the WeddellBasin of the Weddell Sea, and their slopes (Fig. 1).Two comparative samples were taken further northin the adjacent Agulhas and southern Cape Basins,which are separated from each other by the AgulhasRidge. The major South Atlantic deep-sea basinsstarted forming during Jurassic and Cretaceoustimes in connection with the Gondwana break-upand seafloor spreading (Brandt et al., 2004a, 2007;Lawver and Gahagan, 2003). The Weddell Basin isseparated from the northerly basins by the South-west India Ridge (LaBrecque, 1986). The PowellBasin on the western side of the Weddell Sea wasformed in the Tertiary by geological processes

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opening the Drake Passage and tectonic movementsin the Scotia Sea (Lawver and Gahagan, 2003;Mitchell et al., 2000).

The oceanography of the deep South Atlanticseafloor is defined by its prominent water mass, theAntarctic Bottom Water (Tomczak and Godfrey,2001). The Antarctic Bottom Water expands north-wards into the Atlantic basins east and west of theMid-Atlantic Ridge, like the Agulhas Basin, but canonly enter the basins north of the Walvis Ridge(e.g., Cape Basin) via the northerly RomancheFracture Zone. The Weddell Sea Bottom Water(WSBW), defined by a temperature of !0.7 1C anda salinity of 34.64 ppt (Orsi et al., 1993), is themain water mass above the Weddell Sea benthos(Fahrbach et al., 2001). The WSBW flows from thewestern Weddell Sea into the Scotia Sea and SouthSandwich Forearc, and its circulation is drivenby the Weddell Sea gyre (e.g., Fahrbach et al.,1994; Orsi et al., 1993, 1995). The sediments in thebathyal and abyssal Weddell and Powell Basins aredominated by silt and clay (Howe et al., 2004,unpublished data).

2.2. Collection and treatment of samples

A 3-m wide Agassiz trawl (AGT) was deployed attwo locations in the South Atlantic and 14 locations

in the Southern Ocean during the PFS Polarsternexpedition ANT XXII/3 WECCON 2005—ANDEEP III in January–April 2005 (Fahrbach,2006) (Table 1; Fig. 1). The sample depths rangedfrom 1047 to 4931m, sampling continental slopes ofthe eastern Weddell Sea (off Kapp Norvegia)and western Weddell Sea and the South OrkneyIslands, and deep Cape, Agulhas, Weddell andPowell Basins (Fig. 1). At the stations 074-7,078-11 and 081-9, the cod end mesh size was10mm, while at all other stations, an inlet of500 mm mesh size was inserted. The 500 mm meshsize was used because of smaller adult size of deep-sea macrobenthos compared to shelf macrobenthos(Gray, 2002). The deployment protocol was stan-dardised to 10min trawling at 1 knot with 1.5"cable length to water depth to facilitate compar-ability between the different sites. At station 059-10,the AGT was trawled for 20min. The haul distanceswere calculated from the time the Agassiz trawltravelled on the ground. The tension meter of thewinch clearly indicated when the AGT left theseabed. Haul length varied from 731 to 3841m(Table 1).

Sample volumes were estimated and the generalsediment composition was noted (Table 1). Sedi-ment data analysis from core samples taken at thesame sample locations was done by John Howe

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Fig. 1. Locations of the Agassiz trawl stations sampled during ANDEEP III in the Southern Ocean and South Atlantic.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–18631850

(SAMS, UK) (www.cedamar.org, ANDEEP IIIsediment data).

When the trawl reached the deck, each sample(for volumes, see Table 1) was separated on a500-mm sieve. Mega- and larger macrofauna wereseparated by eye on deck and the residues in thesieves were fixed in pre-cooled 96% ethanol. After48 h fixation at +8 1C, the sieve residue was sortedunder stereomicroscope. The taxa of each trawlsample were identified to morphospecies level. Thenumber of morphospecies and specimens werecounted to determine the abundance and speciesrichness of major taxonomic groups. For faunalanalysis, organisms were assigned to 1 of 44taxonomic groups (Table 2). To enable comparisonsbetween stations, the number of individuals werestandardised to 1000m2 trawled area hauls. Thetimes and positions when the AGT reached and leftthe seafloor were used to calculate trawl length tocompensate for the fact that the trawl cannot beclosed. Biomass measurements were not taken.

Comparisons of community compositions be-tween stations were done using Bray–Curtis simila-rities (Bray and Curtis, 1957). Bray–Curtis scores of

the relative abundance of each taxon were analysedas a dendrogram using PRIMER 5 (Clarke andWarwick, 2001). The relative abundances were usedto compensate for the semi-quantitative nature ofthe AGT data.

3. Results

In the abyssal basins of the Southern Ocean andSouth Atlantic, more than 5900 specimens belong-ing to 12 phyla, at least 26 classes and at least44 orders, were sampled from 16 AGT catches(Tables 2 and 3). There was a significant positivecorrelation between morphospecies richness andabundance at stations (t-test: p ¼ 0.001, T ¼ 3.596,d.f. ¼ 30). The stations with the highest account ofmorphospecies and abundance levels were 057-2,074-7 and 121-7 (all Weddell Sea). The major sixtaxa (Cnidaria, Mollusca, Annelida, Crustacea,Echinodermata and Chordata) occurred at allstations, but only echinoderms, crustaceans andmolluscs dominated the species composition. Ex-amples for high species richness in relation toabundance were 58 crustacean morphospecies in

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Table 1Details of Agassiz trawl (AGT) stations of the Southern Ocean cruise, ANDEEP III

Area AGT Station Date Depth (m) Latitude Longitude Haul

length

(m)

Volume

(L)

Sediment

sand/silt/

clay (%)Start End Start End

CB 1 PS67/016-11 26.01.05 4699–4730 4117.460S 4117.420S 9155.110E 9154.920E 3577 20 4/54/42

AB 2 PS67/021-8 29.01.05 4579–4579 47139.190S 47139.030S 4116.500E 4116.510E 3525 30 17/68/15

WS 3 PS67/057-2 10.02.05 1819–1822 69124.500S 69124.620S 5119.370W 5119.680W 1436 4200 Soft

sediment

WS 4 PS67/059-10 15.02.05 4648–4648 67130.370S 67130.270S 013.740E 014.340E 2619 50 5/70/25,

dropstones

WS 5 PS67/074-7 20.02.05 1055–1047 71118.480S 71118.400S 13158.550W 13158.140W 813 50 Dropstones

WS 6 PS67/078-11 21.02.05 2147–2147 7119.390S 7119.350S 13159.330W 13158.810W 1588 4200 Soft

sediment,

dropstones

WS 7 PS67/080-6 22.02.05 3006–2978 70140.230S 70140.420S 14143.780W 14143.830W 1977 4200 16/58/26,

dropstones

WS 8 PS67/081-9 24.02.05 4390–4392 70132.940S 70133.150S 14134.400W 14134.100W 2743 1 No sediment

WS 9 PS67/088-11 27.02.05 4930–4931 6813.580S 6813.570S 20124.580W 20124.220W 3641 150 2/64/34

WS 10 PS67/094-11 02.03.05 4893–4894 66138.050S 66138.100S 2715.900W 2715.460W 3488 o200 Soft

sediment

WS 11 PS67/102-11 06.03.05 4794–4797 65135.400S 65135.510S 36129.000W 36128.830W 3841 4300 1/47/52

WS 12 PS67/110-2 09.03.05 4701–4704 6510.790S 6510.850S 4310.410W 4310.250W 3298 4300 Soft

sediment,

dropstones

WS 13 PS67/121-7 14.03.05 2616–2617 63134.920S 63134.650S 50141.970W 50141.680W 2424 4500 Soft

sediment

PB 14 PS67/142-6 18.03.05 3403–3404 6219.930S 6219.800S 49130.470W 49130.590W 2323 4500 3/66/31

PB 15 PS67/150-7 20.03.05 1970–1954 61148.320S 61148.200S 47128.450W 47128.640W 2064 100 Soft

sediment

PB 16 PS67/151-1 20.03.05 1181–1188 61145.460S 61145.340S 4717.570W 4717.780W 731 100 Soft

sediment

The area abbreviations are: AB, Agulhas Basin; CB, Cape Basin; PB, Powell Basin; WS, Weddell Sea.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–1863 1851

272 crustacean specimens at station 121-7 (WesternWeddell Sea) and 49 polychaete species in 727individuals. The mean number of species over allstations was 59, the averaged number of specimens.

A positive effect of the small-sized (500 mm) innernet and cod end on the collection quantify wasobserved. Macro- and megafaunal groups likemolluscs, crustaceans, poriferans and polychaetes

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Table 2Morphospecies richness of macro- and megazoobenthic taxa in AGT samples

Phylum Class CB AB WS WS WS WS WS WS WS WS WS WS WS PB PB PB016-11

021-8

057-2

059-10

074-7

078-11

080-6

081-9

088-10

094-11

102-11

110-2

121-7

142-6

150-5

151-1

Porifera 0 0 2 3 20 6 4 0 4 5 7 1 17 2 1 1Cnidaria Hydrozoa 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0

Scyphozoa 0 0 0 0 0 0 0 1 0 1 0 0 0 1 1 0Anthozoa Alcyonacea (soft

cor.)0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0

Alcyonacea(gorg.)

0 0 0 0 0 2 0 0 0 0 0 0 0 1 0 0

Pennatulacea 0 1 0 1 1 0 0 0 1 1 1 0 0 1 0 0Actiniaria 1 1 2 1 4 0 1 0 1 1 1 1 0 4 0 2Corallimorpharia 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0Scleractinia 0 0 1 0 0 1 0 0 0 0 0 0 0 1 0 0Zoanthidea 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1Ceriantharia 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0Antipatharia 0 0 0 1 0 0 0 0 1 1 1 1 0 0 0 0

Nemertea 1 0 2 0 1 1 0 0 0 0 0 0 1 0 0 0Mollusca Bivalvia 16 10 5 5 2 4 6 0 7 7 8 4 4 12 4 3

Gastropoda Prosobranchia 7 1 11 0 1 1 9 0 1 1 3 1 2 11 7 1Opisthobranchia 5 1 2 0 0 2 0 0 0 0 0 0 0 2 0 0

Polyplacophora 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0Scaphopoda 5 5 4 0 0 4 1 0 1 1 3 1 1 2 1 0Cephalopoda Octopoda 0 0 1 1 1 0 0 0 0 0 0 0 2 0 0 1

Teuthida 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0Annelida Polychaeta Sedentaria 4 1 19 1 2 11 4 0 4 2 5 4 39 24 5 4

Errantia 6 1 9 0 0 4 0 0 4 3 2 0 10 10 4 3Sipunculida 0 0 1 0 0 1 0 0 0 1 1 0 5 1 1 2Echiurida 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1Crustacea Ostracoda 7 0 1 0 0 0 1 1 2 9 1 1 0 1 5 1

Cirripedia Thoracica 0 0 0 1 0 0 0 0 0 0 0 0 1 1 0 0Malacostraca Amphipoda 0 1 3 1 0 1 0 0 1 2 1 1 17 19 9 3

Tanaidacea 0 0 3 1 0 0 4 0 4 1 1 0 14 8 1 1Cumacea 0 0 4 0 0 0 0 0 1 1 1 1 1 2 3 0Isopoda 0 0 8 1 3 2 4 0 6 11 2 5 15 23 12 1Mysidacea 1 1 1 0 1 1 0 0 0 1 2 0 0 0 2 0Natantia 1 0 1 0 1 1 0 0 0 1 0 0 0 0 1 1

Chelicerata Pycnogonida 0 0 0 1 2 0 0 0 0 0 0 1 3 0 2 3Tentaculata Bryozoa 1 1 0 0 3 5 0 0 0 0 1 0 3 0 0 0

Brachiopoda 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0 0Echinodermata Ophiuroidea 3 5 4 4 7 3 7 1 1 2 1 2 3 8 5 5

Asteroidea 2 2 6 2 5 4 2 1 2 6 1 0 2 5 1 1Echinoidea Regularia 1 0 0 0 0 2 0 0 0 0 0 0 1 1 10 1

Irregularia 0 0 1 0 0 1 0 0 0 0 0 0 1 3 0 0Crinoidea 0 0 3 0 2 0 0 0 0 0 0 0 0 2 1 1Holothuroidea 9 5 11 4 11 9 0 0 2 10 3 0 3 7 7 7

Chordata Ascidiacea 0 0 1 1 0 0 2 0 2 1 1 0 1 1 7 1Pisces 1 3 1 2 3 3 0 1 1 2 0 1 1 1 2 2

Totals 72 40 110 32 72 72 45 6 47 71 47 25 148 122 84 40

The area abbreviations are: AB, Agulhas Basin; CB, Cape Basin; PB, Powell Basin; WS, Weddell Sea.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–18631852

were high in richness and abundance. The small-sized inner net also collected many typicallylarger faunal elements like sponges, cnidarians andfishes.

3.1. Taxon richness

The numbers of preliminary identified species andmorphospecies found per station ranged from 6 at

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Table 3Numbers of specimens per macro- and megazoobenthic taxon collected in AGT samples

Phylum Class CB AB WS WS WS WS WS WS WS WS WS WS WS PB PB PB016-11

021-8

057-2

059-10

074-7

078-11

080-6

081-9

088-10

094-11

102-11

110-2

121-7

142-6

150-5

151-1

Porifera 0 0 2 3 50 15 4 0 4 6 90 100 52 3 1 1Cnidaria Hydrozoa 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0

Scyphozoa 0 0 0 0 0 0 0 1 0 1 0 0 0 1 1 0Anthozoa Alcyonacea (soft

cor.)0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0

Alcyonacea(gorg.)

0 0 0 0 0 4 0 0 0 0 0 0 0 1 0 0

Pennatulacea 0 1 0 2 1 0 0 0 2 2 3 0 0 1 0 0Actiniaria 1 1 8 1 9 0 1 0 2 2 2 1 0 6 0 2Corallimorpharia 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0Scleractinia 0 0 6 0 0 8 0 0 0 0 0 0 0 1 0 0Zoanthidea 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1Ceriantharia 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0Antipatharia 0 0 0 3 0 0 0 0 5 2 15 9 0 0 0 0

Nemerteans 3 0 2 0 5 3 0 0 0 0 0 0 1 0 0 0Mollusca Bivalvia 117 70 67 7 7 20 54 0 35 86 45 23 10 184 6 11

Gastropoda Prosobranchia 10 1 30 0 1 1 18 0 1 1 6 1 4 37 13 3Opisthobranchia 67 4 70 0 0 2 0 0 0 0 0 0 0 3 0 0

Polyplacophora 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0Scaphopoda 6 11 118 0 0 42 8 0 4 2 23 4 31 15 4 0Cephalopoda Octopoda 0 0 1 1 1 0 0 0 0 0 0 0 3 0 0 2

Teuthida 0 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0Annelida Polychaeta Sedentaria 10 1 137 1 3 26 6 0 4 3 10 5 664 111 8 8

Errantia 7 6 54 0 0 9 0 0 9 4 2 0 63 23 6 3Sipunculida 0 0 21 0 0 6 0 0 0 2 3 0 23 1 1 2Echiurida 0 0 0 0 0 0 0 0 0 0 0 0 4 1 1 1Crustacea Ostracoda 9 0 3 0 0 0 1 1 2 28 2 1 0 1 5 1

Cirripedia Thoracica 0 0 0 1 0 0 0 0 0 0 0 0 4 3 0 0Malacostraca Amphipoda 0 2 29 1 0 1 0 0 5 8 1 1 107 31 12 4

Tanaidacea 0 0 18 1 0 0 4 0 8 4 1 0 95 31 1 1Cumacea 0 0 39 0 0 0 0 0 1 2 1 1 1 9 5 0Isopoda 0 0 19 2 6 6 6 0 11 30 3 11 67 66 14 1Mysidacea 6 1 7 0 5 3 0 0 0 2 4 0 0 0 7 0Natantia 5 0 20 0 290 153 0 0 0 1 0 0 0 0 133 51

Chelicerata Pycnogonida 0 0 0 1 10 0 0 0 0 0 0 1 4 0 2 4Tentaculata Bryozoa 4 2 0 0 7 5 0 0 0 0 5 0 3 0 0 0

Brachiopoda 0 0 2 0 0 3 0 0 0 0 0 0 0 0 0 0Echinodermata Ophiuroidea 100 50 25 9 129 5 78 2 1 19 2 2 22 148 5 22

Asteroidea 2 5 26 6 7 9 3 1 4 6 1 0 3 50 1 2Echinoidea Regularia 1 0 0 0 0 14 0 0 0 0 0 0 10 50 10 33

Irregularia 0 0 1 0 0 2 0 0 0 0 0 0 2 57 0 0Crinoidea 0 0 4 0 30 0 0 0 0 0 0 0 0 30 4 3Holothuroidea 50 16 69 34 49 72 0 0 2 20 7 0 5 44 22 72

Chordata Ascidiacea 0 0 1 1 0 0 4 0 2 1 1 0 2 1 3 1Pisces 1 4 4 2 3 3 0 1 1 2 0 1 1 1 4 4

Abbreviations: AB, Agulhas Basin; CB, Cape Basin; PB, Powell Basin; WS, Weddell Sea.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–1863 1853

station 081-9 (eastern slope of Weddell Sea) to 148at the western Weddell Sea slope station 121-7(Fig. 2; Table 1). Highest species numbers werefound along the continental slopes in depthsbetween 1800 and 3400m. Morphospecies richnessin the abyssal plain stations (4300–4900m) was ingeneral lower than in the slope stations with theexceptions of the stations 016-11 in the Cape Basinand 094-11 in the Weddell Basin, where more than70 species were found (Fig. 2). The most frequenttaxon were ophiuroids occurring in all 16 stations.Bivalves, polychaetes and asteroids were found at 15stations (Table 2). Sedentary polychaetes were themost speciose taxon at a single station with 39/24morphospecies found at the western Weddell Seastation 121-7 and the Powell Basin station 142-6,followed by isopods (23 species at 142-6 and 17species at 121-7) and sponges (20 species at 074-7 inthe eastern Weddell Sea at Kapp Norvegia). Amongthe polychaetes, the families Cirratulidae, Malani-dae and Paraonidae were richest. The richest isopodfamilies were those with small-sized species, suchas the families Acanthaspidiidae, Munnopsidae,Desmosomatidae and Haploniscidae. Sponge richness

was dominated by the class Demospongiae, with30 species so far identified, especially by thefamilies Cladorhizidae (carnivore sponges) andPolymastiidae. However, 14 species of Hexactinelli-da, especially of the family Rossellidae (glasssponges) and 3 species of the class Calcarea, allprobably new to science, were also found (apreliminary list of the sponge species fromANDEEP I-III is given by Janussen and Tendal,2007). Within the Mollusca, turrid gastropodsand taxodont bivalves of the families Nuculanidaeand Yoldiidae, respectively, were most speciose.There was no distinct gradient in taxonomic rich-ness with increasing depth from the upper con-tinental slope to the abyssal basins (Fig. 3). Taxonfrequencies were changed considerably betweenstations as well as between depths. At most stations,malacostracan crustaceans, polychaetes and bi-valves were most species-rich accounting each for10–30% of the present taxa (30–60% together).Sponges were most dominant with 28% at theshallowest station (074-7, eastern Weddell Sea) at1055m, but represented just 2–9% of the taxa at theother stations.

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0

30

60

90

120

150

074-7

151-1

057-2

150-5

078-1

1

121-7

080-6

142-6

081-9

021-8

059-1

0

016-1

1

110-2

102-1

1

094-1

1

088-1

0

Speci

es

num

be

rs p

er

class

Porifera Cnidaria Nemerteans Mollusca Annelida Sipunculida

Echiurida Crustacea Chelicerata Tentaculata Echinodermata Chordata

Fig. 2. Species richness by phylum and AGT station. The AGT stations are ranked by depth, from shallowest on the left.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–18631854

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074-7 1055 m 151-1 1181 m 057-2 1819 m

150-5 1970 m 078-11 2147 m 121-7 2616 m

080-6 3006 m 142-6 3403 m 021-8 4579 m

059-10 4648 m 016-11 4699 m 110-2 4701 m

102-11 4794 m 094-11 4893 m 088-10 4930 m

Porifera Hydrozoa Scyphozoa Anthozoa Nemerteans

Bivalvia Gastropoda Polyplacophora Scaphopoda Octopoda

Polychaeta Sipunculida Echiurida Cirripedia Malacostraca

Pycnogonida Bryozoa Brachiopoda Ophiuroidea Asteroidea

Echinoidea Crinoidea Holothuroidea Ascidiacea Pisces

Fig. 3. Proportions of morphospecies by higher taxa in the abyssal Southern Ocean and South Atlantic sorted by depth.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–1863 1855

Among the 45 species of sponges were 14 speciesof Hexactinellida, and eurybathic Polymastidae andMyxillidae as well as 3 species of predatoryCladorhizidae (all Demospongiae) and three calcar-eous species. Caulophacus (Oxydiscus) weddelliJanussen, Tabachnick and Tendal, 2004 was col-lected for the first time since its initial discovery(Janussen et al., 2004), and the biggest and onlycomplete specimen of Malacosaccus coatsi Topsent,1910 was collected. Among the anthozoan mor-phospecies identified were 10 Octocorallia and 26Hexacorallia of which the actiniarians were mostdiverse with 16 species. The anthozoan fauna atdepths below 4000m were mainly represented byGalatheantheumum profundale (Carlgren, 1956),Umbellula cf. thomsoni Kolliker, 1874 and Anti-patharia gen.1. A total of 53 gastropod morphos-pecies were identified, often represented by singlespecimens like the newly described Bathylepetalinseae Schwabe, 2006. Bivalves were representedby 43 species and scaphopods by 7 species, and 4species of ooctopodiform cephalopodes also werefound in the samples. Polyplacophora were repre-sented by the sole record of Stenosemus simplicissi-mus (Thiele, 1906) at the shallowest Station 074-7.The peracarids dominated the crustaceans, espe-cially small-sized isopods and amphipods, but alsolarger taxa like serolids of the genus Acanthoserolisand the amphipod Epimeria cf. inermis Walker,1903 were found. Natant decapods were representedby the deep-water genus Nematocarcinus. Among

the Brachiopoda only inarticulate forms of thegenus Pelagodiscus were found. Echinoids wererepresented by the eurybathic regular taxa Sterechi-nus agassizii Mortensen, 1910, Ctenocidaris nutrixMortensen, 1928 and Aporocidaris milleri Morten-sen, 1909 and the deep-water irregular taxa Antre-chinus, Plexechinus and Echinosigra. Holothuroideawere diverse with at least 40 morphospecies in-cluding, cosmopolitan species like Psychropoteslongicauda Theel, 1882 and Scotoplanes globosa(Theel, 1879) and as yet unidentified species.Ascidians were represented by colonial and stalkedtaxa. Fish were represented by tripod fish in theAfrican basins and grenadiers (Macrouridae) in theWeddell Basin.

3.2. Abundance

Malacostracan crustaceans were the most abun-dant taxon with more than 1300 individuals(Table 3). This was influenced by the occurrenceof the shrimp Nematocarcinus, which found at sevenstations and accounted for 653 specimens. The nextmost abundant groups were the polychaetes (1183specimens) and bivalves (742 specimens). Hydro-zoans and polyplacophorans were present withonly a single specimen each at the Weddell Basinstation 88-10 (the former) and station 074-7 onthe eastern Weddell Sea slope. Zoobenthic composi-tion based on relative abundances per taxonrevealed differences between the stations, but no

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Fig. 4. Relative abundance of macro- and megazoobenthic taxa. Taxa with minor abundances are pooled in ‘‘others’’: Hydrozoa, Scyphozoa,Anthozoa, Nemerteans, Gastropoda, Polyplacophora, Scaphopoda, Sipunculida, Echiurida, Cirripedia, Pycnogonida, Bryozoa, Brachiopoda,Asteroidea, Crinoidea and Pisces.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–18631856

general consistent pattern was found (Fig. 4). Theproportion of bivalves increased with increasingdepth (t-test po0.001, T ¼ 9.473, d.f. ¼ 30). Mala-costraca dominated stations along the slope,but were also important at some of the deepeststations. Ophiuroids were most important at sta-tions between 3000 and 4500m (e.g., stations080-6, 142-6, 021-8). The importance of holothur-ians (which had the highest biomass, estimatedby sample volume) varied between stations anddepth.

Abundances per 1000m2 ranged from 0.9 indivi-duals (hereafter abbreviated ind) at 081-9 to 252ind at 074-7, both at the eastern Weddell Sea slope(Fig. 5). The stations on the two continental slopes(074-7 to 142-6 in Fig. 5, 1055–3403m (depth)showed significantly higher abundances (median118.5 indm!2) than the stations in the basins(081-9 to 088-10, 4579–4930m depth; median16.5 indm!2). The two transects taken down thecontinental slopes at Kapp Norvegia/easternWeddell Sea and Powell Basin/western WeddellSea presented contrasting patterns. Whilst at KappNorvegia species richness and abundance decreasedwith increasing depth, the opposite trend wasobserved in the Powell Basin (Fig. 6).

The cluster analysis showed a separation ofstations into clusters at a similarity of about70% (Fig. 7), with exception of the eastern WeddellSea station, 081-9 station, which had just38% similarity. The stations in the Cape andAgulhas Basins formed a group as did those inPowell Basin.

4. Discussion

4.1. Taxon richness

The results of the current study suggest thathigher taxon richness of the bathyal and abyssalWeddell Sea (e.g., at phylum, class and order levels)can be as diverse as that of other Antarctic and sub-Antarctic shelf habitats (e.g., Arnaud et al., 1998;Arntz and Brey, 2003; Arntz et al., 2005, 2006;Ramos, 1999; Rehm et al., 2006; VoX, 1988). Thezoobenthos compositions of the ANDEEP III AGTcollections we report here show a higher taxondiversity than similarly collected AGT data ofANDEEP I and II (Allcock et al., 2003). Thesedifferences may be explained by important changesin the AGT deployment between the cruises. DuringANDEEP I and II, a 1-m wide trawl with 10-mmcod end was used, whilst during ANDEEP III, a3-m wide trawl with 500-mm cod end was used. Bothtaxon composition and quantity on the recent cruiseincreased compared to ANDEEP I and II (Allcocket al., 2003; Futterer et al., 2003). Especially speciesof sizes less than 10mm were caught morefrequently and in higher specimen numbers. Casualobservations suggest that the megafauna that wascollected with the 3-m trawl with 500-mm cod endcontained many more holothurians and cnidarians.Considerably more small-sized sponge species,particularly important deep-sea taxa, such Clador-hizidae and abyssal Calcarea, were collected duringthis cruise compared to earlier cruises (Janussen,2006; Janussen et al., 2004; Janussen and Tendal,

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Fig. 7. Station dendrogram from the Cluster analysis. Brey–Curtis Index, group average method.

K. Linse et al. / Deep-Sea Research II 54 (2007) 1848–18631858

2007). On the other hand, amphipods that occurredat most of the former stations during ANDEEP Iand II were very rare this time.

On high taxonomic levels macro- and megafaunalcomposition of abyssal Antarctic soft-bottom habi-tats is comparable to those of deep-sea and Arctic(e.g., Bluhm et al., 2005; Deubel, 2000; Gage, 1978;Kroncke, 1998). Polychaetes, the most speciosetaxon in this study, are often a dominant elementof the deep benthic faunas in the Antarctic (Hilbig,2001, 2004; Montiel et al., 2005), the Atlantic andPacific (Glover et al., 2001, 2002; Hilbig and Blake,2006) and Arctic (Bluhm et al., 2005; Kroncke,1998; Narayanaswamy et al., 2005). Malacostracancrustaceans and bivalves, speciose in the Antarcticsamples, are also known to be species rich in thedeep Atlantic and Arctic oceans (Brandt, 1995;Brandt et al., 2005a; Olabarria, 2005; Rex et al.,2000; Richling, 2000). Sponges, the dominant andcharacteristic group of the Antarctic shelf (Arntzet al., 1994; Barthel and Tendal, 1994), are lessprominent in the deep but still speciose, andespecially the glass sponges are more diverseon higher taxonomic levels (genera and families)(D. Janussen et al., 2004, unpublished data).

The number of morphospecies reported in theANDEEP III AGT samples, ranging from 6 to 148per trawl, is lower than that of Antarctic shelf sites.Arntz et al. (2005) reported between 99 and 306species in 17 trawls taken on the eastern WeddellSea shelf in 230–855m depth. Trawls collected at theisolated sub-Antarctic island of Bouvet reported46–98 species per sample (Arntz et al., 2006). Thedecrease in species numbers with increasing waterdepth towards the abyssal basins (44000m) ob-served in the current study fits the common knowl-edge on bathymetric trends in deep-sea fauna(Carney, 2005; Gage and Tyler, 1991). More specificinformation on the species composition of selectedtaxa can obtained from the of ANDEEP III cruisereport (Fahrbach, 2006).

4.2. Abundance

Most of the abundance assessments of Antarcticmacrobenthos have been carried out using grabsand corers (e.g., Gerdes et al., 1992; Montiel et al.,2005; Piepenburg et al., 2002 and references there-in). The use of trawled devices like AGTs, dredgesand sledges for abundance studies has been criti-cised for being of semi-quantitative nature (Elefth-eriou and Holme, 1984). On the other hand, the

trawls are more efficient to assess macro- andmegafaunal diversity in an area (Rehm et al.,2006). Various methods have been used to quantifytrawl catches. One method is to use devices thatclose when they leave the seafloor (Brandt andBarthel, 1995; Brenke, 2005). Another method forbottom and Agassiz trawls is to take subsamples ofeither representative volume per catch (VoX, 1988),of 5-L volume per catch (Arnaud et al., 1998) or 5-Lvolume per catch (Arntz et al., 1996, 2006). Here, weanalysed the complete trawl catches and calculatedthe trawl length between the points when the trawlreached and left the seafloor.

This is the first study on the abundance of macro-and megafaunal assemblages in the Antarctic deep-sea. Similar studies on the relative abundances ofthe Antarctic shelf and the Arctic shelf and deep-seazoobenthos used lower taxonomic resolution, eitherphylum level (Arntz et al., 2006; Bluhm et al., 2005;Feder et al., 2005; Rehm et al., 2006) or a mixture ofphyla and classes (Kroncke, 1998) or pooledstations (Arnaud et al., 1998; Ingole, 2003).Comparisons with these studies therefore can onlybe made to their levels and then the relative range oftaxon abundances in our study is similar to theirs.

The standardised abundances per 1000m2 (1 and252 ind 1000m!2) decrease with increasing depthand were very low at depths over 4500m. Otherbenthos studies have previously found a decline inabundance with increasing depth (e.g., Rex et al.,2006; Saunders and Hessler, 1969; Soltwedel, 2000).The vertical transects collected at the continentalslopes at Kapp Norvegia/eastern Weddell Sea andin the Powell Basin/western Weddell Sea showedopposing patterns in abundance. At Kapp Norvegiaabundances decreased with increasing depth whilstin the Powell Basin no obvious decrease was found.Such findings support previously suggested (supra-benthos) abundance increases with depth in someareas of the Weddell Sea and decreases with depthin other areas (e.g., Halley Bay and in the BransfieldStrait, see Linse et al., 2002). At depths of1000–3500m on continental slopes, abundances ofmacrobenthos are more variable and seem to bevery patchy across scales measured to date (Brandtet al., 2005b; Kaiser et al., 2007). Previously, patchydistribution patterns have been suggested forbivalves (Linse, 2004) and isopods (Brandt et al.,2004a) from analysis of ANDEEP I and IIexpeditions. Compared to macrofaunal abundancesfrom the Antarctic shelf collected by grabs(16–14.483 indm!2, see Arntz et al., 2005) the

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deep-sea abundances are orders of magnitude lower.It is likely that these results are linked to limited andpatchy food availability for deep-sea benthos(Schwinghammer, 1985; Rice et al., 1990; Smithet al., 1997; Soltwedel, 2000).

The ANDEEP II expedition made first insightspossible into the deep macro- and megabenthicassemblages of Antarctic waters. The results re-ported here agree with the well-documented dom-inances of polychaetes, malacostracan crustaceans,bivalves and ophiuroids in the deep sea and on soft-bottom habitats supplemented by holothurians,gastropods and sponges. Further investigations ofthe Antarctic deep-sea habitats are needed for amore detailed faunal inventory, species level com-munity and diversity analyses, and a better under-standing of the ecological processes.

Acknowledgements

We are grateful to the German Science Founda-tion and all national funding agencies for thefinancial support given to us for our participationin ANDEEP III. Thanks are due to EberhardFahrbach, Chief Scientist (AWI) on ANT XXII/3,and to the captain and crew of PFS Polarstern forhelp and support on board. We are grateful toDavid Barnes (BAS) for helpful comments on themanuscript. Peter Fretwell (BAS) provided theinitial ANDEEP III station map. Vonda Cummings(NIWA) and Sven Thatje (NOCS) are thanked forproviding helpful criticisms of the manuscript.

This is ANDEEP publication #70 and a con-tribution to the SCAR EBA programme.

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