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ELSEVIER Deep-Sea Research II 54 (2007) 1848-1863 www.elsevier.com/locate/dsr2

Macro- and megabenthic assemblages in the bathyal and abyssal () Katrin Linsea’*, Angelika Brandtb, Jens M. Bohnc, Bruno Danisd, Claude De Broyerd, Brigitte Ebbe6, Vincent Heterierf, Dorte Janussen8, Pablo J. López González11, Myriam Schüller1/ Enrico Schwabe6, Michael R.A. Thomson1

aBritish Antarctic Survey, Natural Environmental Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK bZoologisches Institut und Museum, Universität Hamburg, Martin-Luther-King Platz 3, D-20147 Hamburg, Germany c Zoologische S taats Sammlung München, Münchhausens tr. 21, D-81247 München, Germany dRoyal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000 Bruxelles, Belgium eForschungsinstitut Senckenberg, DZMB-CeDAMar, c/o Forschungsmuseum König, Adenauerallee 160, D-53113 Bonn, Germany fUniversité 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 Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla, Avda. Reina Mercedes 6, E-41012 Sevilla, Spain íSchool of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK

Accepted 6 July 2007 Available online 3 August 2007

Abstract

The assemblages inhabiting the continental shelf around are known to be very patchy, in large part due to deep iceberg impacts. The present study shows that richness and abundance of much deeper benthos, at slope and abyssal depths, also vary greatly in the Southern and South Atlantic oceans. On the ANDEEP III expedition, we deployed 16 Agassiz trawls to sample the zoobenthos at depths from 1055 to 4930 m across the northern Weddell Sea and two South Atlantic basins. A total of 5933 specimens, belonging to 44 higher taxonomic groups, were collected. Overall the most frequent 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 most abundant taxa accounted for 10-30% each of all taxa present. Standardised abundances based on trawl catches varied between 1 and 252 individuals per 1000 m2. Abundance significantly decreased with increasing depth, and assemblages showed high patchiness in their distribution. Cluster analysis based on relative abundance showed changes of community structure that were not linked to depth, area, sediment grain size or temperature. Generally abundances of zoobenthos in the abyssal Weddell Sea are lower than shelf abundances by several orders of magnitude. © 2007 Elsevier Ltd. All rights reserved.

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

* Corresponding author. Tel.: + 44 1223 221 631; fax: +441223 221259. E-mail address: [email protected] (K. Linse).

0967-0645/$ - see front matter © 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr2.2007.07.011 K. Linse et aí / Deep-Sea Research I I 54 (2007) 1848-1863 1849

1. Introduction tion are much better known (e.g., Arnaud et al., 1998; Arntz et al., 1994, 2005; Dayton et al., 1994; In the last three decades, since the discoveries of Ramos, 1999; Voß, 1988). To date most studies of abyssal hydrothermal vents and manganese no­ abundance in shelf communities and assemblages dules, scientific and commercial interest in studying have focussed on gaining quantitative assessments the global deep oceans has increased greatly (e.g., of soft-bottom habitats (Gambi and Bussotti, 1999; Bluhm, 1994; Decraemer and Gourbault, 1997; Gerdes et al., 1992, 2003; Lovell and Tregi, 2003; Lambshead et al., 2002; Tyler et al., 2002; Van Piepenburg et al., 2002; Saiz-Salinas and Ramos, Dover et al., 2003; Van Dover and Lutz, 2004). Sites 1999; Saiz-Salinas et al., 1997). Macrobenthic in the deep North Atlantic and Pacific oceans have community abundance assessments using semi- especially become the focus of long-term projects, quantitative methods (dredges, sledges and trawls) and what started as descriptive research there has have been undertaken by Voß (1988) in the Weddell moved into process-orientated investigations (Bett Sea, by Arnaud et al. (1998) in the South Shetland et al., 2001; Billett et al., 2001; Narayanaswamy Islands, and by Rehm et al. (2006) in the . et al., 2005). Much less is known about the deep-sea Barry et al. (2003) analysed the shelf and upper assemblages of the Arctic, Indo-Pacific and South­ slope assemblages in the Ross Sea by using towed ern oceans (Bluhm et ah, 2005; Brandt et ah, 2004a; camera footage. Linse et al. (2002) investigated the Ingole, 2003; Kröncke, 1998; Wlodarska-Kowalczuk suprabenthic fauna in the Weddell Sea and the et al., 2004). About half the world’s surface is South Shetland Islands. On many Antarctic benthic abyssal yet only tiny areas have been visited and we expeditions, the relative abundances of macro- and know very little of the biodiversity and abundance megabenthic taxa were assessed on variable of animals there (Rex et ah, 2006). One of the least- point classifications from absent to very abundant known abyssal areas surrounds Antarctica, the deep (Allcock et al., 2003; Arnaud et al., 1998; Arntz and Southern Ocean. Gutt, 1997, 1999; Arntz and Brey, 2003; Arntz et al., For more than a century, deep-water samples 2006) but no numerical data were collected. have occasionally been taken in the Southern During ANDEEP III, the faunal assemblages Ocean. Most of these studies, such as the Russian collected by Agassiz trawl were assessed by higher expeditions with R.V.s Ob, Akademik Kurchatov taxon classification and numerical data taken and Dmitriy Mendeleev (Malyutina, 2004 and allowing comparison with faunal assemblages from references therein) and American expeditions with the Antarctic shelf. This paper is the first attempt to USNS Eltanin and R.V. Hero (Dell, 1990), con­ describe deep-sea mega- and macrobenthic assem­ centrated on describing and discovering species. blages of the Weddell Sea and their abundances. Assessments of macro- or megafaunal abundances, community structure or richness levels were see­ 2. Material and methods mingly not considered. The recent ANDEEP expeditions to the Antarctic and South Atlantic 2.1. Study area have greatly increased our knowledge of faunal abundances in the deep sea (Brandt et al., 2004b). Four study regions were selected, but the main During the ANDEEP I and II expeditions, benthic focus was on the Powell Basin and the Weddell fauna was sampled in bathyal and abyssal depths Basin of the Weddell Sea, and their slopes (Fig. 1). (1121-6348m) of the Shackleton Fracture Zone, the Two comparative samples were taken further north northern Weddell Sea Basin, and the South in the adjacent Agulhas and southern Cape Basins, Sandwich Islands. However, most studies have been which are separated from each other by the Agulhas restricted to specific taxonomic groups (Brandt Ridge. The major South Atlantic deep-sea basins et al., 2004b; Cornelius and Gooday, 2004; Linse, started forming during Jurassic and Cretaceous 2004) or meiofauna (Gutzmann et al., 2004; times in connection with the Gondwana break-up Vanhove et al., 2004) and macrofauna (Blake and and seafloor spreading (Brandt et al., 2004a, 2007; Narayanaswamy, 2004). Information about deep Lawver and Gahagan, 2003). The Weddell Basin is megabenthic assemblages, communities and abun­ separated from the northerly basins by the South­ dances across taxa is still scarce (Brandt, 2005). In west India Ridge (LaBrecque, 1986). The Powell contrast to the nearly unknown deep sea, the Basin on the western side of the Weddell Sea was Antarctic shelf fauna and its community composi­ formed in the Tertiary by geological processes 1850 K. Linse et a!. / Deep-Sea Research I I 54 (2007) 1848-1863

80°W 70" 60" 50° 40" 30° 20° 10° 0° 10° 20° 30°E

South Africa

C ape Basin

40° S - *016-11 - 40° S

Aghulas Ridge

*021-8 Agulhas Basin

50° - - 50°

Southwest Indian Ridge Scotia Sea

60° - 60° 150-7 * • 151-1 142-6

; . 121-7* Weddell Basin

081-9 70° S 0 8 0 -6I # - 70° S 078-11 Dronning Maud Land

80°W 70° 60° 50° 40° 30°/ 20° 10° 0° 10° 20° 30°E Fig. 1. Locations of the Agassiz trawl stations sampled during ANDEEP III in the Southern Ocean and South Atlantic. opening the Drake Passage and tectonic movements in the Southern Ocean during the PFS Polarstern in the Scotia Sea (Lawver and Gahagan, 2003; expedition ANT XXII/3 WECCON 2005— Mitchell et al., 2000). ANDEEP III in January-April 2005 (Fahrbach, The oceanography of the deep South Atlantic 2006) (Table 1; Fig. 1). The sample depths ranged seafloor is defined by its prominent water mass, the from 1047 to 4931 m, sampling continental slopes of Antarctic Bottom Water (Tomczak and Godfrey, the eastern Weddell Sea (off Kapp Norvegia) 2001). The Antarctic Bottom Water expands north­ and western Weddell Sea and the South Orkney wards into the Atlantic basins east and west of the Islands, and deep Cape, Agulhas, Weddell and Mid-Atlantic Ridge, like the Agulhas Basin, but can Powell Basins (Fig. 1). At the stations 074-7, only enter the basins north of the Walvis Ridge 078-11 and 081-9, the cod end mesh size was (e.g., Cape Basin) via the northerly Romanche 10 mm, while at all other stations, an inlet of Fracture Zone. The Weddell Sea Bottom Water 500 pm mesh size was inserted. The 500 pm mesh (WSBW), defined by a temperature of —0.7 °C and size was used because of smaller adult size of deep- a salinity of 34.64 ppt (Orsi et ah, 1993), is the sea macrobenthos compared to shelf macrobenthos main water mass above the Weddell Sea benthos (Gray, 2002). The deployment protocol was stan­ (Fahrbach et al., 2001). The WSBW flows from the dardised to 10 min trawling at 1 knot with 1.5 x western Weddell Sea into the Scotia Sea and South cable length to water depth to facilitate compar­ Sandwich Forearc, and its circulation is driven ability between the different sites. At station 059-10, by the Weddell Sea gyre (e.g., Fahrbach et al., the AGT was trawled for 20 min. The haul distances 1994; Orsi et al., 1993, 1995). The sediments in the were calculated from the time the Agassiz trawl bathyal and abyssal Weddell and Powell Basins are travelled on the ground. The tension meter of the dominated by silt and clay (Howe et al., 2004, winch clearly indicated when the AGT left the unpublished data). seabed. Haul length varied from 731 to 3841m (Table 1). 2.2. Collection and treatment o f samples Sample volumes were estimated and the general sediment composition was noted (Table 1). Sedi­ A 3-m wide Agassiz trawl (AGT) was deployed at ment data analysis from core samples taken at the two locations in the South Atlantic and 14 locations same sample locations was done by John Howe K. Linse et aí. / Deep-Sea Research 1154 (2007) 1848-1863 1851

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

Area AGT Station Date Depth (m) Latitude Longitude Haul Volume Sediment length (L) sand/silt/ Start End Start End (m) clay (%)

CB 1 PS67/016-11 26.01.05 4699-4730 41°7.46'S 41°7.42'S 9°55.11'E 9°54.92'E 3577 20 4/54/42 AB 2 PS67/021-8 29.01.05 4579-4579 47°39.19'S 47°39.03'S 4°16.50'E 4°16.5TE 3525 30 17/68/15 WS 3 PS67/057-2 10.02.05 1819-1822 69°24.50'S 69°24.62'S 5° 19.37'W 5°19.68'W 1436 >200 Soft sediment WS 4 PS67/059-10 15.02.05 4648-4648 67°30.37'S 67°30.27'S 0°3.74'E 0°4.34'E 2619 50 5/70/25, dropstones WS 5 PS67/074-7 20.02.05 1055-1047 71°18.48'S 71°18.40'S 13°58.55'W 13°58.14'W 813 50 Dropstones WS 6 PS67/078-11 21.02.05 2147-2147 71°9.39'S 71°9.35'S 13°59.33'W 13°58.8TW 1588 >200 Soft sediment, dropstones WS 7 PS67/080-6 22.02.05 3006-2978 70°40.23'S 70°40.42'S 14°43.78'W 14°43.83'W 1977 >200 16/58/26, dropstones WS 8 PS67/081-9 24.02.05 4390-4392 70°32.94'S 70°33.15'S 14°34.40'W 14°34.10'W 2743 1 No sediment WS 9 PS67/088-11 27.02.05 4930-4931 68°3.58'S 68°3.57'S 20°24.58'W 20°24.22'W 3641 150 2/64/34 WS 10 PS67/094-11 02.03.05 4893-4894 66°38.05'S 66°38.10'S 27°5.90'W 27°5.46'W 3488 <200 Soft sediment WS 11 PS67/102-11 06.03.05 4794-4797 65°35.40'S 65°35.51'S 36°29.00'W 36°28.83'W 3841 >300 1/47/52 WS 12 PS67/110-2 09.03.05 4701-4704 65°0.79'S 65°0.85'S 43°0.4TW 43°0.25'W 3298 >300 Soft sediment, dropstones WS 13 PS67/121-7 14.03.05 2616-2617 63°34.92'S 63°34.65'S 50°41.97'W 50°41.68'W 2424 >500 Soft sediment PB 14 PS67/142-6 18.03.05 3403-3404 62°9.93'S 62°9.80'S 49°30.47'W 49°30.59'W 2323 >500 3/66/31 PB 15 PS67/150-7 20.03.05 1970-1954 61°48.32'S 61°48.20'S 47°28.45'W 47°28.64'W 2064 100 Soft sediment PB 16 PS67/151-1 20.03.05 1181-1188 61°45.46'S 61°45.34'S 47°7.57'W 47°7.78'W 731 100 Soft sediment

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

(SAMS, UK) (www.cedamar.org, ANDEEP III the relative abundance of each taxon were analysed sediment data). as a dendrogram using PRIMER 5 (Clarke and When the trawl reached the deck, each sample Warwick, 2001). The relative abundances were used (for volumes, see Table 1) was separated on a to compensate for the semi-quantitative nature of 500-(rm sieve. Mega- and larger macrofauna were the AGT data. separated by eye on deck and the residues in the sieves were fixed in pre-cooled 96% ethanol. After 3. Results 48 h fixation at + 8 °C, the sieve residue was sorted under stereomicroscope. The taxa of each trawl In the abyssal basins of the Southern Ocean and sample were identified to morphospecies level. The South Atlantic, more than 5900 specimens belong­ number of morphospecies and specimens were ing to 12 phyla, at least 26 classes and at least counted to determine the abundance and species 44 orders, were sampled from 16 AGT catches richness of major taxonomic groups. For faunal (Tables 2 and 3). There was a significant positive analysis, organisms were assigned to 1 of 44 correlation between morphospecies richness and taxonomic groups (Table 2). To enable comparisons abundance at stations (Y-test: p — 0.001, T — 3.596, between stations, the number of individuals were d.f. = 30). The stations with the highest account of standardised to 1000 m2 trawled area hauls. The morphospecies and abundance levels were 057-2, times and positions when the AGT reached and left 074-7 and 121-7 (all Weddell Sea). The major six the seafloor were used to calculate trawl length to taxa (Cnidaria, Mollusca, Annelida, Crustacea, compensate for the fact that the trawl cannot be Echinodermata and Chordata) occurred at all closed. Biomass measurements were not taken. stations, but only echinoderms, crustaceans and Comparisons of community compositions be­ molluscs dominated the species composition. Ex­ tween stations were done using Bray-Curtis simila­ amples for high species richness in relation to rities (Bray and Curtis, 1957). Bray-Curtis scores of abundance were 58 crustacean morphospecies in 1852 K. Linse et al. / Deep-Sea Research 1154 (2007) 1848-1863

Table 2 Morphospecies 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 PB om ­ 021- 057- 059- 074- 078- 080- 081- 088- 094- 102- 110- 121- 142- 150- 151- ii 8 2 10 7 11 6 9 10 11 11 2 7 6 5 1

Porifera 0 0 2 3 20 6 4 0 4 5 7 1 17 2 1 1 Cnidaria 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 0 Anthozoa Alcyonacea (soft 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 cor.) Alcyonacea 0 0 0 0 0 2 0 0 0 0 0 0 0 1 0 0 (g°rg.) Pennatulacea 0 1 0 1 1 0 0 0 1 1 1 0 0 1 0 0 Actiniaria i 1 2 1 4 0 1 0 1 1 1 1 0 4 0 2 Corallimorpharia 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 Scleractinia 0 0 1 0 0 1 0 0 0 0 0 0 0 1 0 0 Zoanthidea 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 Ceriantharia 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 Antipatharia 0 0 0 1 0 0 0 0 1 1 1 1 0 0 0 0 Nemertea i 0 2 0 1 1 0 0 0 0 0 0 1 0 0 0 Mollusca 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 1 Opisthobranchia 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 0 Scaphopoda 5 5 4 0 0 4 1 0 1 1 3 1 1 2 1 0 Cephalopoda 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 0 Annelida 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 3 Sipunculida 0 0 1 0 0 1 0 0 0 1 1 0 5 1 1 2 Echiurida 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 Crustacea 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 0 Malacostraca 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 1 Cumacea 0 0 4 0 0 0 0 0 1 1 1 1 1 2 3 0 Isopoda 0 0 8 1 3 2 4 0 6 11 2 5 15 23 12 1 Mysidacea 1 1 1 0 1 1 0 0 0 1 2 0 0 0 2 0 Natantia 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 3 T entaculata 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 0 Echinodermata 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 1 Echinoidea 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 0 Crinoidea 0 0 3 0 2 0 0 0 0 0 0 0 0 2 1 1 Holothuroidea 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 1 Pisces 1 3 1 2 3 3 0 1 1 2 0 1 1 1 2 2

T otals 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.

272 crustacean specimens at station 121-7 (Western A positive effect of the small-sized (500 pm) inner Weddell Sea) and 49 polychaete species in 727 net and cod end on the collection quantify was individuals. The mean number of species over all observed. Macro- and megafaunal groups like stations was 59, the averaged number of specimens. molluscs, crustaceans, poriferans and polychaetes K. Linse et al. / Deep-Sea Research I I 54 (2007) 1848-1863 1853

Table 3 Numbers 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 PB om ­ 021- 057- 059- 074- 078- 080- 081- 088- 094- 102- 110- 121- 142- 150- 151- ii 8 2 10 7 11 6 9 10 11 11 2 7 6 5 1

Porifera 0 0 2 3 50 15 4 0 4 6 90 100 52 3 1 1 Cnidaria 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 0 Anthozoa Alcyonacea (soft 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 cor.) Alcyonacea 0 0 0 0 0 4 0 0 0 0 0 0 0 1 0 0 (g°rg.) Pennatulacea 0 1 0 2 1 0 0 0 2 2 3 0 0 1 0 0 Actiniaria i 1 8 1 9 0 1 0 2 2 2 1 0 6 0 2 Corallimorpharia 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 Scleractinia 0 0 6 0 0 8 0 0 0 0 0 0 0 1 0 0 Zoanthidea 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 1 Ceriantharia 0 0 2 0 0 0 0 0 0 0 0 0 0 0 0 0 Antipatharia 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 0 Mollusca 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 3 Opisthobranchia 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 0 Scaphopoda 6 11 118 0 0 42 8 0 4 2 23 4 31 15 4 0 Cephalopoda 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 0 Annelida 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 3 Sipunculida 0 0 21 0 0 6 0 0 0 2 3 0 23 1 1 2 Echiurida 0 0 0 0 0 0 0 0 0 0 0 0 4 1 1 1 Crustacea 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 0 Malacostraca 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 1 Cumacea 0 0 39 0 0 0 0 0 1 2 1 1 1 9 5 0 Isopoda 0 0 19 2 6 6 6 0 11 30 3 11 67 66 14 1 Mysidacea 6 1 7 0 5 3 0 0 0 2 4 0 0 0 7 0 Natantia 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 4 Tentaculata 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 0 Echinodermata 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 2 Echinoidea 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 0 Crinoidea 0 0 4 0 30 0 0 0 0 0 0 0 0 30 4 3 Holothuroidea 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 1 Pisces 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.

were high in richness and abundance. The small­ 3.1. Taxon richness sized inner net also collected many typically larger faunal elements like sponges, cnidarians and The numbers of preliminary identified species and fishes. morphospecies found per station ranged from 6 at 1854 K. Linse et al. 1 Deep-Sea Research I I 54 (2007) 1848-1863 station 081-9 (eastern slope of Weddell Sea) to 148 was dominated by the class Demospongiae, with at the western Weddell Sea slope station 121-7 30 species so far identified, especially by the (Fig. 2; Table 1). Highest species numbers were families Cladorhizidae (carnivore sponges) and found along the continental slopes in depths Polymastiidae. However, 14 species of Hexactinelli­ between 1800 and 3400 m. Morphospecies richness da, especially of the family Rossellidae (glass in the abyssal plain stations (4300-4900 m) was in sponges) and 3 species of the class Calcarea, all general lower than in the slope stations with the probably new to science, were also found (a exceptions of the stations 016-11 in the Cape Basin preliminary list of the sponge species from and 094-11 in the Weddell Basin, where more than ANDEEP I-III is given by Janussen and Tendal, 70 species were found (Fig. 2). The most frequent 2007). Within the Mollusca, turrid gastropods taxon were ophiuroids occurring in all 16 stations. and taxodont bivalves of the families Nuculanidae Bivalves, polychaetes and asteroids were found at 15 and Yoldiidae, respectively, were most speciose. stations (Table 2). Sedentary polychaetes were the There was no distinct gradient in taxonomic rich­ most speciose taxon at a single station with 39/24 ness with increasing depth from the upper con­ morphospecies found at the western Weddell Sea tinental slope to the abyssal basins (Fig. 3). Taxon station 121-7 and the Powell Basin station 142-6, frequencies were changed considerably between followed by isopods (23 species at 142-6 and 17 stations as well as between depths. At most stations, species at 121-7) and sponges (20 species at 074-7 in malacostracan crustaceans, polychaetes and bi­ the eastern Weddell Sea at Kapp Norvegia). Among valves were most species-rich accounting each for the polychaetes, the families Cirratulidae, Malani- 10-30% of the present taxa (30-60% together). dae and Paraonidae were richest. The richest isopod Sponges were most dominant with 28% at the families were those with small-sized species, such shallowest station (074-7, eastern Weddell Sea) at as the families Acanthaspidiidae, Munnopsidae, 1055 m, but represented just 2-9% of the taxa at the Desmosomatidae and Haploniscidae. Sponge richness other stations.

150

120

m m0 o 0 90 C l U3 -Q0 £ =5 C S 60 - 'o0 Q. C/D

30 -

CM u? CD CD 0 3 CO O CM O ó Ó CM Ó IO IO LO CO CM CO CO CM 0 3 CD CM CO o O o O O IO O 03 CO o o o ^ o o □ Porifera □ Cnidaria □ Nemerteans □ Mollusca □ Annelida □ Sipunculida ■ Echiurida 0 Crustacea 0 Chelicerata H Tentaculata □ Echinodermata E 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 aí / Deep-Sea Research I I 54 (2007) 1848-1863 1855

1%1%2% e u

13% 26% 074-7 1055 m 151-1 1181 m 057-2 1819m

<«2% 2^%1%5% il

32% m 3% 150-5 1970 m 078-11 2147 m 121-7 2616 m

8% 8% , 5H^%11«%

9% 2%

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

17% 9% " 059-10 4648 m 016-11 4699 m 110-2 4701 m

2% 3% 8%

27% 18% 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. 1856 K. Linse et aí / Deep-Sea Research I I 54 (2007) 1848-1863

Among the 45 species of sponges were 14 species the Brachiopoda only inarticulate forms of the of Hexactinellida, and eurybathic Polymastidae and genus Pelagodiscus were found. Echinoids were Myxillidae as well as 3 species of predatory represented by the eurybathic regular taxa Sterechi­ Cladorhizidae (all Demospongiae) and three calcar­ nus agassizii Mortensen, 1910, Ctenocidaris nutrix eous species. Caulophacus (Oxydiscus) weddelli Mortensen, 1928 and Aporocidaris milleri M orten­ Janussen, Tabachnick and Tendal, 2004 was col­ sen, 1909 and the deep-water irregular taxa Antre­ lected for the first time since its initial discovery chinus, Plexechinus and Echinosigra. Holothuroidea (Janussen et al., 2004), and the biggest and only were diverse with at least 40 morphospecies in­ complete specimen ofMalacosaccus coatsi Topsent, cluding, cosmopolitan species like Psychropotes 1910 was collected. Among the anthozoan mor­ longicauda Théel, 1882 and Scotoplanes globosa phospecies identified were 10 Octocorallia and 26 (Théel, 1879) and as yet unidentified species. Hexacorallia of which the actiniarians were most Ascidians were represented by colonial and stalked diverse with 16 species. The anthozoan fauna at taxa. Fish were represented by tripod fish in the depths below 4000 m were mainly represented by African basins and grenadiers (Macrouridae) in the Galatheantheumum profundale (Carlgren, 1956), Weddell Basin. Umbellula cf. thomsoni Kolliker, 1874 and Anti­ patharia gen.l. A total of 53 gastropod morphos­ 3.2. Abundance pecies were identified, often represented by single specimens like the newly described Bathylepeta Malacostracan crustaceans were the most abun­ linseae Schwabe, 2006. Bivalves were represented dant taxon with more than 1300 individuals by 43 species and scaphopods by 7 species, and 4 (Table 3). This was influenced by the occurrence species of ooctopodiform céphalopodes also were of the shrimp Nematocarcinus, which found at seven found in the samples. Polyplacophora were repre­ stations and accounted for 653 specimens. The next sented by the sole record of Stenosemus simplicissi­ most abundant groups were the polychaetes (1183 mus (Thiele, 1906) at the shallowest Station 074-7. specimens) and bivalves (742 specimens). Hydro- The peracarids dominated the crustaceans, espe­ zoans and polyplacophorans were present with cially small-sized isopods and amphipods, but also only a single specimen each at the Weddell Basin larger taxa like serolids of the genus Acanthoserolis station 88-10 (the former) and station 074-7 on and the amphipod Epimeria cf. inermis Walker, the eastern Weddell Sea slope. Zoobenthic composi­ 1903 were found. Natant decapods were represented tion based on relative abundances per taxon by the deep-water genus Nematocarcinus. Among revealed differences between the stations, but no

100%

80% -

60% - 40% - 1 20 % -

0% I I i^- Y — i^ Y m-Y o -'-YYYo

H Porifera □ Bivalvia B Polychaeta □ Malacostraca 0 Ophiuroidea ■ Holothuroidea H Cephalopoda □ others

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 aí / Deep-Sea Research I I 54 (2007) 1848-1863 1857 general consistent pattern was found (Fig. 4). The 4. Discussion proportion of bivalves increased with increasing depth (t-testp <0.001, T — 9.473, d.f. = 30). M ala­ 4.1. Taxon richness costraca dominated stations along the slope, but were also important at some of the deepest The results of the current study suggest that stations. Ophiuroids were most important at sta­ higher taxon richness of the bathyal and abyssal tions between 3000 and 4500 m (e.g., stations Weddell Sea (e.g., at phylum, class and order levels) 080-6, 142-6, 021-8). The importance of holothur- can be as diverse as that of other Antarctic and sub- ians (which had the highest biomass, estimated Antarctic shelf habitats (e.g., Arnaud et al., 1998; by sample volume) varied between stations and Arntz and Brey, 2003; Arntz et al., 2005, 2006; depth. Ramos, 1999; Rehm et al., 2006; Voß, 1988). The Abundances per 1000 m2 ranged from 0.9 indivi­ zoobenthos compositions of the ANDEEP III AGT duals (hereafter abbreviated ind) at 081-9 to 252 collections we report here show a higher taxon ind at 074-7, both at the eastern Weddell Sea slope diversity than similarly collected AGT data of (Fig. 5). The stations on the two continental slopes ANDEEP I and II (Allcock et al., 2003). These (074-7 to 142-6 in Fig. 5, 1055-3403 m (depth) differences may be explained by important changes showed significantly higher abundances (median in the AGT deployment between the cruises. During 118.5 ind m-2) than the stations in the basins ANDEEP I and II, a 1-m wide trawl with 10-mm (081-9 to 088-10, 4579^1930m depth; median cod end was used, whilst during ANDEEP III, a 16.5 ind m-2). The two transects taken down the 3-m wide trawl with 500-(un cod end was used. Both continental slopes at Kapp Norvegia/eastern taxon composition and quantity on the recent cruise Weddell Sea and Powell Basin/western Weddell increased compared to ANDEEP I and II (Allcock Sea presented contrasting patterns. Whilst at Kapp et al., 2003; Fütterer et al., 2003). Especially species Norvegia species richness and abundance decreased of sizes less than 10 mm were caught more with increasing depth, the opposite trend was frequently and in higher specimen numbers. Casual observed in the Powell Basin (Fig. 6). observations suggest that the megafauna that was The cluster analysis showed a separation of collected with the 3-m trawl with 500-|rm cod end stations into clusters at a similarity of about contained many more holothurians and cnidarians. 70% (Fig. 7), with exception of the eastern Weddell Considerably more small-sized sponge species, Sea station, 081-9 station, which had just particularly important deep-sea taxa, such Clador­ 38% similarity. The stations in the Cape and hizidae and abyssal Calcarea, were collected during Agulhas Basins formed a group as did those in this cruise compared to earlier cruises (Janussen, Powell Basin. 2006; Janussen et al., 2004; Janussen and Tendal,

300.0

250.0

° 200.0

- 50.0

00.0

Stations: from shallow to deep

Fig. 5. Macro- and megabenthos abundance per 1000nr. The grey line marks the slope stations. 1858 K. Linse et aí / Deep-Sea Research I I 54 (2007) 1848-1863

(A) 300

250 —

o 200 - - - o

150 252

131 106

50 44 PB

KN/WS 1000 2000 3000 Depth (m) (B) 140

120 —

2000 3000 KN/WS Depth (m)

Fig. 6. Patterns in (A) abundance per 1000 m2 and (B) species richness along two vertical transects at Kapp Norvegia and in the Powell Basin. Abbreviations: KN/WS, Kapp Norvegia/Weddell Sea; PB, Powell Basin.

20

40 I bp CO 60 'tl o1 3

0 80 CQ 100 0 3 ° N- o p CM CO CD1111 N N CM Ó ó T CM O t- h - 00 O) 0 0 CM M- IO CM LO O LO 00 O)

CB/AB PB

Fig. 7. Station dendrogram from the Cluster analysis. Brey-Curtis Index, group average method. K. Linse et aí / Deep-Sea Research I I 54 (2007) 1848-1863 1859

2007). On the other hand, amphipods that occurred trawls are more efficient to assess macro- and at most of the former stations during ANDEEP I megafaunal diversity in an area (Rehm et ah, and II were very rare this time. 2006). Various methods have been used to quantify On high taxonomic levels macro- and megafaunal trawl catches. One method is to use devices that composition of abyssal Antarctic soft-bottom habi­ close when they leave the seafloor (Brandt and tats is comparable to those of deep-sea and Arctic Barthel, 1995; Brenke, 2005). Another method for (e.g., Bluhm et al., 2005; Deubel, 2000; Gage, 1978; bottom and Agassiz trawls is to take subsamples of Kröncke, 1998). Polychaetes, the most speciose either representative volume per catch (Voß, 1988), taxon in this study, are often a dominant element of 5-L volume per catch (Arnaud et al., 1998) or 5-L of the deep benthic faunas in the Antarctic (Hilbig, volume per catch (Arntz et al., 1996, 2006). Here, we 2001, 2004; Montiel et al., 2005), the Atlantic and analysed the complete trawl catches and calculated Pacific (Glover et ah, 2001, 2002; Hilbig and Blake, the trawl length between the points when the trawl 2006) and Arctic (Bluhm et al., 2005; Kröncke, reached and left the seafloor. 1998; Narayanaswamy et al., 2005). Malacostracan This is the first study on the abundance of macro- crustaceans and bivalves, speciose in the Antarctic and megafaunal assemblages in the Antarctic deep- samples, are also known to be species rich in the sea. Similar studies on the relative abundances of deep Atlantic and Arctic oceans (Brandt, 1995; the Antarctic shelf and the Arctic shelf and deep-sea Brandt et al., 2005a; Olabarria, 2005; Rex et al., zoobenthos used lower taxonomic resolution, either 2000; Richling, 2000). Sponges, the dominant and phylum level (Arntz et ah, 2006; Bluhm et al., 2005; characteristic group of the Antarctic shelf (Arntz Feder et al., 2005; Rehm et al., 2006) or a mixture of et ah, 1994; Barthel and Tendal, 1994), are less phyla and classes (Kröncke, 1998) or pooled prominent in the deep but still speciose, and stations (Arnaud et al., 1998; Ingole, 2003). especially the glass sponges are more diverse Comparisons with these studies therefore can only on higher taxonomic levels (genera and families) be made to their levels and then the relative range of (D. Janussen et al., 2004, unpublished data). taxon abundances in our study is similar to theirs. The number of morphospecies reported in the The standardised abundances per 1000 m2 (1 and ANDEEP III AGT samples, ranging from 6 to 148 252 ind 1000 m-2) decrease with increasing depth per trawl, is lower than that of Antarctic shelf sites. and were very low at depths over 4500 m. Other Arntz et al. (2005) reported between 99 and 306 benthos studies have previously found a decline in species in 17 trawls taken on the eastern Weddell abundance with increasing depth (e.g., Rex et ah, Sea shelf in 230-855 m depth. Trawls collected at the 2006; Saunders and Hessler, 1969; Soltwedel, 2000). isolated sub-Antarctic island of Bouvet reported The vertical transects collected at the continental 46-98 species per sample (Arntz et al., 2006). The slopes at Kapp Norvegia/eastern Weddell Sea and decrease in species numbers with increasing water in the Powell Basin/western Weddell Sea showed depth towards the abyssal basins (> 4000 m) ob­ opposing patterns in abundance. At Kapp Norvegia served in the current study fits the common knowl­ abundances decreased with increasing depth whilst edge on bathymetric trends in deep-sea fauna in the Powell Basin no obvious decrease was found. (Carney, 2005; Gage and Tyler, 1991). More specific Such findings support previously suggested (supra- information on the species composition of selected benthos) abundance increases with depth in some taxa can obtained from the of ANDEEP III cruise areas of the Weddell Sea and decreases with depth report (Fahrbach, 2006). in other areas (e.g., Hailey Bay and in the Bransfield Strait, see Linse et al., 2002). At depths of 4.2. Abundance 1000-3500 m on continental slopes, abundances of macrobenthos are more variable and seem to be Most of the abundance assessments of Antarctic very patchy across scales measured to date (Brandt macrobenthos have been carried out using grabs et al., 2005b; Kaiser et al., 2007). Previously, patchy and corers (e.g., Gerdes et al., 1992; Montiel et al., distribution patterns have been suggested for 2005; Piepenburg et al., 2002 and references there­ bivalves (Linse, 2004) and isopods (Brandt et ah, in). The use of trawled devices like AGTs, dredges 2004a) from analysis of ANDEEP I and II and sledges for abundance studies has been criti­ expeditions. Compared to macrofaunal abundances cised for being of semi-quantitative nature (Elefth- from the Antarctic shelf collected by grabs eriou and Holme, 1984). On the other hand, the (16-14.483 ind m -2, see Arntz et al., 2005) the 1860 K. Linse et aí / Deep-Sea Research I I 54 (2007) 1848-1863 deep-sea abundances are orders of magnitude lower. Arntz. W.E.. Gutt. L. 1999. The expedition ANTARKTIS XV/3 It is likely that these results are linked to limited and (EASIZ II) of RV “Polarstern" in 1998. Berichte zur patchy food availability for deep-sea benthos Polarforschung 301. 1-229. Arntz. W.E.. Brey. T.. Gallardo. V.A.. 1994. Antarctic benthos. (Schwinghammer, 1985; Rice et al., 1990; Smith Oceanography and Marine Biology: An Annual Review 32. et al., 1997; Soltwedel, 2000). 241-304. The ANDEEP II expedition made first insights Arntz. W.E.. Gorny. M.. Lardies. M.A.. Mutschke. E.. Rios. C.. possible into the deep macro- and megabenthic 1996. Benthic macrofauna sampled with the Agassiz trawl. In: assemblages of Antarctic waters. The results re­ Arntz. W.E.. Gorny. M. (Eds.). Cruise Report of the Joint Chilean-German-Italian Magellan “Victor Hensen" Cam­ ported here agree with the well-documented dom­ paign in 1994. Berichte zur Polarforschung 190. pp. 43-51. inances of polychaetes, malacostracan crustaceans, Arntz. W.E.. Thatje. S.. Gerdes, D.. Gili. J.-M., Gutt. J., Jacob. bivalves and ophiuroids in the deep sea and on soft- U.. Montiel. A.. Orejas. C.. Teixido. N.. 2005. The bottom habitats supplemented by holothurians, Antarctic—Magellan connection: macrobenthos ecology on gastropods and sponges. Further investigations of the shelf and upper slope, a progress report. Scientia Marina 69. 237-269. the Antarctic deep-sea habitats are needed for a Arntz. W.E.. Thatje. S.. Linse. K.. Avila. C.. Ballesteros. M.. more detailed faunal inventory, species level com­ Barnes. D.. Cope. T.. Cristobo. F.. De Broyer. C.. Gutt. J.. munity and diversity analyses, and a better under­ Isla. E.. López-González. P.. Montiel. A.. Munilla, T.. Ramos standing of the ecological processes. Esplá, A.. Raupach. M.. Rauschert. M.. Rodriguez. E.. Teixidó, N.. 2006. Missing link in the Southern Ocean: sampling the marine benthic fauna of remote Bouvet Island. Polar Biology 29. 83-96. Acknowledgements Barry. J.B.. Grebmeier. J.M.. Smith. J.. Dunbar. R.B.. 2003. Oceanographic versus seafloor-habitat control of benthic We are grateful to the German Science Founda­ megafaunal communities in the S.W. Ross Ses. Antarctica. tion and all national funding agencies for the In: DiTullio. G.R.. Dunbar. R.B. (Eds.). Biogeochemistry of financial support given to us for our participation the Ross Sea. vol. 78. Antarctic Research Series, pp. 327-354. Barthel. D.. Tendal. O.. 1994. Antarctic hexactinellida. Synopsis in ANDEEP III. Thanks are due to Eberhard of the Antarctic Benthos 6. 1-154. Fahrbach, Chief Scientist (AWI) on ANT XXII/3, Bett. B.J.. Malzone. M.G.. Narayanaswamy. B.E.. Wigham, and to the captain and crew of PFS Polarstern for B.D.. 2001. Temporal variability in phytodetritus and help and support on board. We are grateful to megabenthic activity at the seabed in the deep Northeast David Barnes (BAS) for helpful comments on the Atlantic, Progress in Oceanography 50. 349-368. Billett. D.S.M.. Bett. B.J.. Rice. A.L.. Thurston. M.H.. Galerón. manuscript. Peter Fretwell (BAS) provided the J.. Sibuet, M.. Wolff. G.A.. 2001. Long-term change in the initial ANDEEP III station map. Vonda Cummings megabenthos of the Porcupine Abyssal Plain (NE Atlantic). (NIWA) and Sven Thatje (NOCS) are thanked for Progress in Oceanography 50. 325-348. providing helpful criticisms of the manuscript. Blake. J.A.. Narayanaswamy. B.E.. 2004. 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