This article was downloaded by: [University of Barcelona], [Blanca Figuerola] On: 27 March 2012, At: 10:09 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Systematics and Biodiversity Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tsab20 Spatial patterns and diversity of bryozoan communities from the Southern Ocean: South Shetland Islands, Bouvet Island and Eastern Weddell Sea a b a Blanca Figuerola , Toni Monleón-Getino , Manuel Ballesteros & Conxita Avila a a Departament de Biologia Animal (Invertebrats), Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal, 645, 08028 Barcelona, Spain b Departament d’Estadística, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal, 645, 08028 Barcelona, Spain Available online: 27 Mar 2012 To cite this article: Blanca Figuerola, Toni Monleón-Getino, Manuel Ballesteros & Conxita Avila (2012): Spatial patterns and diversity of bryozoan communities from the Southern Ocean: South Shetland Islands, Bouvet Island and Eastern Weddell Sea, Systematics and Biodiversity, 10:1, 109-123 To link to this article: http://dx.doi.org/10.1080/14772000.2012.668972 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Systematics and Biodiversity (2012), 10(1): 109–123 Research Article Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Spatial patterns and diversity of bryozoan communities from the Southern Ocean: South Shetland Islands, Bouvet Island and Eastern Weddell Sea BLANCA FIGUEROLA1, TONI MONLEÓN-GETINO2, MANUEL BALLESTEROS1 & CONXITA AVILA1 1 Departament de Biologia Animal (Invertebrats), Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal, 645, 08028 Barcelona, Spain 2 Departament d’Estadı́stica, Facultat de Biologia, Universitat de Barcelona, Avda. Diagonal, 645, 08028 Barcelona, Spain (Received 30 November 2011; revised 30 January 2012; accepted 17 February 2012) In this study, we report new data on the biodiversity and the geographic and bathymetric distribution of bryozoans collected during the ANT XXI/2 cruise (November 2003 to January 2004) in the Eastern Weddell Sea and Bouvet Island, and during the Spanish Antarctic expedition ECOQUIM (January 2006) in the South Shetland Islands. Our data on distribution were analysed together with previous studies carried out in the same regions. A total of 54 species of Antarctic bryozoans (206 samples), including a new species of the genus Reteporella were found. Two species were reported for the first time from Bouvet Island, one from the Weddell Sea and one from Spiess Seamount. Fifty-five per cent of all species identified were endemic to Antarctica. In the Weddell Sea, the regions of Austasen and Kapp Norvegia exhibit the highest relative species richness, followed by the Vestkapp region. Multivariate and cluster analyses revealed small-scale spatial variability in the community structure along depth and between localities. Key words: Antarctica, bathymetric distribution, bryozoans, geographic distribution, multidimensional scaling Introduction The conservation and management of marine biodiversity requires detailed studies of the biodiversity and its relationship with environmental conditions (de Voogd et al., 2009). Although they seem to be under less intense pressures when compared with other ecosystems globally, Antarctic habitats are threatened by overexploitation of living resources, establishment of invasive marine species and climate change, as well as the growing impact of tourism (Tejedo et al., 2009). The Antarctic fauna has evolved in stable conditions, thus it is likely to be more sensitive and, for this reason, the risk of extinctions caused by anthropogenic impacts in these ecosystems makes it essential to intensify research on Antarctic biodiversity (Barnes & Peck, 2008). Knowledge of the bryozoan species from the Southern Ocean, their diversity and the environmental conditions in which they live, is still very poor (Kuklinski & Barnes, 2009), which is largely determined by the relative inaccessibility of the region. An understanding of how and why similarities and differences exist between benthic commuCorrespondence to: Blanca Figuerola. E-mail: bfiguerola@ub.edu ISSN 1477-2000 print / 1478-0933 online ! C 2012 The Natural History Museum http://dx.doi.org/10.1080/14772000.2012.668972 nities inhabiting Antarctic ecosystems may provide information about the physical and biological factors that influence bryozoan distributions. More than 700 new species of invertebrates from deep Antarctic waters have been recently discovered, with bryozoans, sponges and amphipods exhibiting high species richness (Brandt et al., 2007). Therefore, recent studies of Antarctic biodiversity in the region have described a rich and varied fauna (Hayward & Winston, 2011). In general, the Antarctic shelf and slope are known to be able to support biomass levels of macrobenthos far higher than those in equivalent habitats in boreal and subtropical regions of equal depth (Arntz et al., 1994). In recent years, the number of taxonomic studies on Antarctic bryozoans has experienced a notable increase (Hayward, 1995; Gutt et al., 2000; López-Fé de la Cuadra & Garcı́a-Gómez, 2000). Since the scientific results of the Belgian Antarctic Expedition in 1897–99 (Waters, 1904), over 300 species have been described and new descriptions continue to appear (Clarke & Johnston, 2003; Gontar, 2008; López & Liuzzi, 2008; Kuklinski & Barnes, 2009; Griffiths, 2010; Figuerola et al., 2012). Cheilostomatid bryozoans are one of the best-represented taxa on the Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 110 B. Figuerola et al. Antarctic shelf (Barnes et al., 2009) and a high proportion (56%) are endemic (Hayward, 1995; Barnes & De Grave, 2000; Clarke & Johnston, 2003; Griffiths et al., 2009; Griffiths, 2010). Many bryozoan species have been reported from the Antarctic Peninsula or the Ross Sea (Hayward, 1995). However, bryozoans are poorly investigated in some other Antarctic regions, such as the Weddell Sea (Zabala et al., 1997; Moyano, 2005, Barnes & Kuklinski, 2010). High levels of biodiversity, with more than 400 species and subspecies of Bryozoa in 32 stations, were found in the first collection from this area during the ANT XIII/3 Expedition (1996) with Polarstern (Arntz & Brey, 2005), and in recent sampling expeditions in the deep Weddell Sea (Arntz & Brey, 2005; Barnes & Kuklinski, 2010). In polar waters, benthic assemblages are characterized by both bathymetric and horizontal variability (Cummings et al., 2006; Smale, 2008). Diversity of Antarctic species is determined by a synergy of physical (depth, substratum, iceberg scouring . . .) and biotic factors (e.g. community type) (Starmans et al., 1999; Smale, 2008; Griffiths, 2010), and in the eastern Weddell Sea shelf, differences in currents cause heterogeneity. Iceberg scouring is the major disturbance affecting the benthos of this continental shelf because it disrupts large areas of the seafloor above 300 m. All of these factors play a key role in structuring recent Antarctic shelf benthic communities (Gutt & Piepenburg, 2003; Thatje et al., 2005; Brandt et al., 2007). The objectives of this research were: (1) to present species-level information on new samples analysed for this study and (2) by combining these with existing data on bryozoan distributions in the region, to describe patterns of distribution in relation to depth and spatial location. Materials and methods Collection methods Samples from the Weddell Sea and Bouvet Island were collected during the Antarctic cruise ANT XXI/2 (from November 2003 to January 2004) of R/V Polarstern (AWI, Bremerhaven, Germany) at 56 stations surveyed. Samples from the South Shetland Islands were collected at three stations (Fig. 1) from the BIO Hespérides in January 2006 during the ECOQUIM cruise. Depths of collections ranged from 27 to 910 m, using Bottom trawl, Agassiz trawl, Rauschert dredge, Epibenthic sledge and Giant box corer in the Weddell Sea and Bouvet Island. In the South Shetland Islands, an Agassiz trawl and a Rock dredge were used instead. Sampling sites were georeferenced and depth was registered at each point (Table 1). After taking pictures of the living animals, the colonies of bryozoans were preserved in 70% ethanol for further taxonomic identification. We classified most of the samples at species level using Hayward (1995). Literature data Some data of sampling stations and their characteristics (Zabala et al., 1997; Barnes & Kuklinski, 2010) and some data of bathymetric ranges and biogeographic distribution of the species studied (Hayward, 1995; Zabala et al., 1997; Gontar & Zabala, 2000; Arntz et al., 2006; Barnes et al., 2008; Barnes & Kuklinski, 2010) came from the literature and Global Biodiversity Information Facility database (GBIF; www.gbif.org). Additional data from South America, New Zealand and South Africa have been obtained from Moyano (1982, 1999), Gordon (1984, 1986) and Florence et al. (2007); see also www.bryozoa.net. Data of Antarctic endemicity came from Hayward (1995), the SCAR’s Marine Biodiversity Information database (SCAR-MarBIN; http://www.scarmarbin.be/) and the Global Biodiversity Information Facility database (GBIF; www.gbif.org). Data analysis In order to obtain representative numbers of individuals and species for the analysis, some data of the same species of bryozoans found in previous cruises in these regions (at 35 stations) were extracted from the literature, and analysed together with our new data from the ANT XXI/2 and ECOQUIM cruises (collected at 59 stations). In total we analysed data from 94 sampling stations. Cluster and non-metric multidimensional scaling (MDS) ordination analyses were performed in order to assess similarities of samples. Due to unequal sampling efforts, binary data (presence/absence) was preferred to make the distance matrix using the Sørensen coefficient. The cluster was then plotted using the single linkage clustering technique to evaluate the similarities in species composition between regions. In order to evaluate the significant differences between regions, a test for binomial proportions was used (P < 0.05). The MDS analysis was used to evaluate the similarities between ranges of depth for the genera because it assumes no shape between variables (Legendre & Legendre, 1998). In order to categorize the continuous variable depth and to represent it in the MDS analysis, it was divided into 100 m interval categories (e.g. 100 m category includes depths from 0–100 m). The first two dimensions were plotted and the distance between dots denotes their similarity measured by the stress value. A stress value of less than 0.1 indicates that the plot accurately represents similarities, while a stress value greater than 0.3 indicates that the points are close to being randomly placed (Clarke, 1993). Bathymetric ranges for each genus sampled in the Weddell Sea are detailed in Table 1. In order to determine whether different assemblages do exist between ranges of depth and neighbouring sites, relative abundance (N) and relative species richness (S, number Spatial patterns and diversity of bryozoan communities 111 Table 1. Sampling stations and their characteristics from this study and from the literature. AT: Agassiz trawl, RD: Rauschert dredge, BT: Bottom trawl, GBC: Giant box corer, ES: Epibenthic sledge, R: Rock dredge, BP: bentopelagic trawl, MG: Multibox corer and GK: large box corer. Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Location Spiess Seamount Bouvet Island Bouvet Island Livingston Livingston Deception Weddell Sea Neumayer Neumayer Neumayer Neumayer Neumayer Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Austasen Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Station Date PS65/345-1 PS65/019-1 PS65/029-1 AGT 7 AGT 6 AGT 9 PS67/102-11 30 30 PS65/069-1 32 31 PS65/121-1 PS65/121-1 PS65/237-1 PS65/336-1 PS65/339-1 PS65/274-1 PS65/265-1 PS65/090-1 PS65/123-1 PS65/132-1 PS65/161-1 PS65/148-1 PS65/173-1 PS65/166-1 PS65/259-1 PS65/175-1 PS65/245-1 PS65/174-1 1 PS65/253-1 PS65/248-1 PS65/039-1 PS65/276-1 PS65/280-1 PS65/279-0 PS65/279-1 PS65/278-1 24 24 2 PS67/078-9 PS67/078-11 PS67/074-6 PS65/232-1 2 2 2 25 25 25 25 25 21 7 6 26 26 11/01/2004 24/11/2003 25/11/2003 06/01/2006 06/01/2006 07/01/2006 06/03/2005 01/03/1996 01/03/1996 07/12/2003 04/03/1996 02/03/1996 11/12/2003 11/12/2003 22/12/2003 05/01/2004 05/01/2004 28/12/2003 27/12/2003 09/12/2003 11/12/2003 12/12/2003 15/12/2003 13/12/2003 16/12/2003 15/12/2003 24/12/2003 16/12/2003 22/12/2003 16/12/2003 05/02/1996 23/12/2003 23/12/2003 05/12/2003 28/12/2003 29/12/2003 29/12/2003 29/12/2003 29/12/2003 21/02/1996 21/02/1996 22/02/1996 21/02/2005 21/02/2005 20/02/2005 21/12/2003 09/02/1996 22/02/1996 22/02/1996 23/02/1996 23/02/1996 23/02/1996 23/02/1996 23/02/1996 18/02/1996 08/02/1996 11/02/1996 24/02/1996 24/02/1996 Latitude (S) Longitude (W) 54◦ 54◦ 54◦ 62◦ 62◦ 63◦ 65◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 70◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 00◦ 08. 31′ 03◦ 13. 97′ 03◦ 13. 05′ 60◦ 44. 827′ 60◦ 43. 683′ 60◦ 36. 355′ 36◦ 29. 00′ 08◦ 20. 00′ 08◦ 20. 00′ 08◦ 37. 43′ 08◦ 15. 10′ 10◦ 44. 20′ 10◦ 34.76′ 10◦ 35. 54′ 10◦ 35. 54′ 10◦ 28. 01′ 10◦ 28. 51′ 10◦ 43. 69′ 10◦ 51. 24′ 10◦ 32. 37′ 10◦ 31. 58′ 10◦ 31. 61′ 10◦ 31. 47′ 10◦ 32. 05′ 10◦ 31. 76′ 10◦ 32. 61′ 10◦ 33. 02′ 10◦ 33. 32′ 10◦ 33. 52′ 10◦ 33. 86′ 11◦ 25. 50′ 11◦ 33. 92′ 11◦ 31. 90′ 11◦ 32. 04′ 11◦ 27. 76′ 11◦ 26. 23′ 11◦ 29. 83′ 11◦ 29. 91′ 11◦ 29. 94′ 11◦ 32. 25′ 11◦ 32. 40′ 12◦ 25. 40′ 13◦ 59. 30′ 13◦ 59. 33′ 13◦ 57. 71′ 13◦ 56. 12′ 12◦ 17. 10′ 12◦ 22. 80′ 12◦ 27. 00′ 14◦ 19. 20′ 14◦ 19. 20′ 14◦ 19. 80′ 14◦ 19. 70′ 14◦ 19. 70′ 21◦ 10. 50′ 13◦ 44. 00′ 13◦ 43. 30′ 14◦ 18. 60′ 14◦ 19. 50′ 44. 12′ 30. 01′ 31. 59′ 41. 575′ 43. 117′ 02. 292′ 35. 40′ 05. 30′ 05. 30′ 25. 87′ 28. 90′ 30. 90′ 50. 08′ 50. 08′ 50. 50′ 50. 75′ 50. 78′ 52. 16′ 52. 75′ 55. 92′ 56. 41′ 56. 42′ 56. 43′ 56. 67′ 56. 82′ 56. 83′ 57. 00′ 57. 11′ 57. 11′ 57. 33′ 03. 10′ 04. 30′ 04. 96′ 06. 30′ 06. 44′ 07. 15′ 07. 43′ 07. 48′ 07. 51′ 08. 15′ 08. 30′ 18. 60′ 09. 39′ 09. 39′ 18. 35′ 18. 61′ 18. 70′ 19. 10′ 19. 20′ 22. 90′ 22. 90′ 23. 10′ 23. 10′ 23. 10′ 26. 50′ 26. 80′ 27. 40′ 29. 30′ 29. 30′ Depth (m) 629.4 259.7 376.8 27.9 94.9 110.3 4794 2315 2315 413.6 286 1586 274 268 264.4 281.2 273.6 290.8 294.8 288 283.2 284.4 279.6 302.4 296.4 338 332.8 337.2 337.2 351.6 462 308.8 286.8 175.2 277.2 228.4 119.2 119.6 120 123 119 181 2156 2157 1030 910 170 159 253 622 622 634 621 628 253 215 212 216 210 Gear References RD This study AT This study AT This study RD This study RD This study AT This study AT Barnes et al. (2010) AG Zabala et al. (1997), DR Zabala et al. (1997) RD Barnes et al. (2010) DR Zabala et al. (1997) DR Zabala et al. (1997) AT This study AT Barnes et al. (2010) BT This study AT This study RD This study BT This study BT This study AT This study GBC This study BT This study AT This study BT This study AT This study BT This study BT This study BT This study BT This study BT This study BT Zabala et al. (1997) BT This study BT This study AT This study AT This study AT This study AT Barnes et al. (2010) AT This study AT Barnes et al. (2010) AG Zabala et al. (1997) GK Zabala et al. (1997) MG Zabala et al. (1997) ES Barnes et al. (2010) AT Barnes et al. (2010) ES Barnes et al. (2010) ES This study AG Zabala et al. (1997) MG Zabala et al. (1997) MG Zabala et al. (1997) AG Zabala et al. (1997) DR Zabala et al. (1997) AG Zabala et al. (1997) GK Zabala et al. (1997) GK Zabala et al. (1997) BP Zabala et al. (1997) GK Zabala et al. (1997) AG Zabala et al. (1997) DR Zabala et al. (1997) DR Zabala et al. (1997) (Continued on next page) 112 B. Figuerola et al. Table 1. (Continued) Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Location Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Kapp Norvegia Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Vestkapp Station Date 29 29 6 6 9 9 9 9 3 5 5 5 4 4 4 PS65/283-1 PS65/297-1 PS65/308-1 20 PS65/292-1 PS65/326-1 PS65/326-1 PS65/324-1 PS65/324-1 PS65/325-1 18 18 17 12 11 21 14 13 15 16 29/02/1996 28/02/1996 08/02/1996 25/02/1996 26/02/1996 10/02/1996 26/02/1996 26/02/1996 26/02/1996 06/02/1996 06/02/1996 07/02/1996 20/02/1996 20/02/1996 20/02/1996 30/12/2003 01/01/2004 02/01/2004 18/02/1996 31/12/2003 03/01/2004 03/01/2004 03/01/2004 03/01/2004 03/01/2004 16/02/1996 16/02/1996 16/02/1996 13/02/1996 13/02/1996 18/02/1996 14/02/1996 14/02/1996 15/02/1996 15/02/1996 Latitude (S) Longitude (W) 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 71◦ 72◦ 72◦ 72◦ 72◦ 72◦ 72◦ 72◦ 72◦ 72◦ 72◦ 73◦ 73◦ 73◦ 73◦ 73◦ 73◦ 73◦ 73◦ 73◦ 73◦ 12◦ 12◦ 13◦ 13◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 12◦ 17◦ 19◦ 19◦ 19◦ 19◦ 19◦ 19◦ 19◦ 19◦ 19◦ 21◦ 21◦ 21◦ 21◦ 21◦ 21◦ 22◦ 22◦ 22◦ 22◦ 30. 70′ 31. 50′ 31. 80′ 32. 10′ 32. 60′ 34. 00′ 34. 70′ 34. 70′ 39. 30′ 39. 75′ 40. 49′ 41. 10′ 41. 20′ 41. 50′ 41. 60′ 32. 16′ 48. 50′ 50. 18′ 50. 50′ 51. 43′ 51, 43′ 51. 70′ 54. 52′ 54. 55′ 54. 76′ 15. 40′ 16. 70′ 18. 00′ 18. 10′ 22. 60′ 22. 90′ 36. 10′ 36. 30′ 42. 00′ 53. 40′ of species present) and P value (test for binomial proportions) were calculated for each depth range and area. A sample-based rarefaction curve was also computed. Chao2, Jacknife1 and Jacknife2 methods were used to estimate the theoretical number of expected species within each area (Colwell & Coddington, 1994). Chao2 is an abundancebased non-parametric estimator of species richness that works by examining the number of species in a sample observed more than once relative to the number of species that is observed just once. In the absence of complete inventories, these non-parametric estimators have been shown to perform better than most other methods, such as observed species richness (Krebs, 1999). Diversity indices are commonly used to provide more information about community composition than simply species richness, such as the rarity and commonness of species and they also take the relative abundances of different species into account. The Margalef index is based on the number of species (species richness), while the oth- 26. 40′ 25. 50′ 34. 50′ 44. 10′ 26. 30′ 25. 80′ 26. 60′ 26. 60′ 05. 10′ 41. 00′ 41. 70′ 44. 30′ 30. 80′ 31. 70′ 29. 40′ 58. 88′ 31. 60′ 35. 94′ 26. 00′ 38. 62′ 38. 67′ 39. 22′ 47. 74′ 47. 30′ 43. 48′ 27. 60′ 25. 50′ 09. 90′ 10. 10′ 10. 60′ 10. 00′ 35. 70′ 19. 10′ 30. 50′ 26. 90′ Depth (m) Gear References 494 504 254 362 570 604 560 560 209 255 254 227 438 436 440 585.2 668 622 428 597.6 616 605.2 693.6 647.2 457.6 1704 1538 468 459 338 283 850 620 446 246 GK BP AG AG AG BT AG DR GK MG EB BT MG GK AG ES RD RD BP BT RD RD RD RD RD AG AG BT BT BT BP BT BT BT BT Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) This study This study This study Zabala et al. (1997) This study This study Barnes & Kuklinski (2010) This study Barnes & Kuklinski (2010) This study Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) Zabala et al. (1997) ers are indices of proportional abundances of the species. The Shannon–Wiener index is strongly influenced by the occurrence of rare species and Simpson’s index by the importance of the more dominant species. Pielou’s (evenness) and Berger–Parker indices calculate the relationship between the observed diversity and the maximum diversity, as well as between the number of the individuals of the most abundant species and the total number of individuals in the sample, respectively (Gray, 2000). Diversity indices are used to assess the impact of disturbances on the marine environment. In this aspect, the Shannon–Wiener index is more sensitive (high values mean an improvement in the environmental state) (Gray, 2000). In the case of the Simpson and Berger–Parker indices, higher values correspond to a lower diversity (Salas et al., 2004; Marqués et al., 2009). The values of diversity indices calculated from the data of the present study of stations sampled with Agassiz trawl (AT), Bottom trawl (BT) and Rauschert dredge (RD) did not show significant differences (bootstrap confidence 113 Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Spatial patterns and diversity of bryozoan communities Fig. 1. Map of the regions of the Weddell Sea, Bouvet Island, Spiess Seamount and the Shetland Islands. Top left: map of all regions; A: Shetland Islands; B: area of Weddell sea; B1: region of Vestkapp; B2: regions of Kapp Norvegia and Austasen; B2-1, B2-2: region of Austasen; C: vicinities of Bouvet Island. interval were overlapping). For this reason, five alpha diversity indices were calculated for each region only in these stations: Margalef (DMg ), Shannon–Wiener (H’), Simpson’s (1 – Lambda’), Pielou’s (J’) and Berger–Parker (B–P). The diversity indices of Kapp Norvegia were not calculated due to the absence of samples collected with any of these trawls in the present study. Statistical significance was established at P < 0.05. Ordination analyses were performed using VegAna software (v.1.6.0; De Cáceres et al., 2003). Diversity analyses (relative abundance and species richness and diversity indices) were carried out with Past (Hammer et al., 2001) and the bootstrap method was used to obtain a more robust non-parametric estimate of the confidence intervals (95%) 114 B. Figuerola et al. (Briggs et al., 1997). The test for binomial proportions was performed with Minitab Statistical Software. The SPSS (version 14.0, SPSS Inc, Chicago, Illinois, USA) package was used for the rest of the data analysis. Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Results A total of 54 species of Antarctic bryozoans (206 samples), belonging to 12 families and 27 genera, were found with different trawls, from depths between 27 and 910 m in the studied areas (Table 2). The list includes a newly described species, Reteporella rosjoarum (Figuerola et al., 2011). Furthermore, two species were reported for the first time from Bouvet Island, one from the Weddell Sea and one from Spiess Seamount. Eight of the species were identified only to genus level. The most diverse Infraorder was Lepraliomorpha with 18 species (33%). Fifty-five per cent of the species found were endemic to the Southern Ocean (see Hayward, 1995, SCAR-MarBIN and GBIF databases), with a total of 49 species. Reteporella with six species was the dominant genus. Most of the species found were Bostrychopora dentata, which represented 9.7% of the total specimens collected, and Nematoflustra flagellata (6.7%). These were followed by Austroflustra vulgaris, Alcyonidium sp., Carbasea curva, Cellarinella nutti and Osthimosia curtioscula. Austroflustra vulgaris was the only species found in the three studied areas from the Weddell Sea. Data from recent cruises reported in the literature and the GBIF database together with our own data were jointly analysed, revealing that four species have been found far from their known distribution range in the Weddell Sea. Therefore, an expansion in their known geographical distribution is reported here (Table 2). Fig. 2. New bathymetric ranges of bryozoans genera from the Southern Ocean found in the present study both from our own data and the literature and the GBIF database. Additional data have been obtained from Hayward (1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006) and Barnes & Kuklinski (2010). genera, (2) a zone between 100 and 700 m characterized by the presence of all of the genera, a similar composition at each depth (77.9% of the genera appear in each 100 m of depth) and the presence of the genus Dakariella only in Bathymetric ranges From a total of 27 genera analysed on the different cruises, 50.2% (16 genera) were restricted to the continental shelf (18 species) and above 900 m. Camptoplites, Melicerita and Cellaria were the only genera found in deeper waters (5900, 4802 and 4531 m, respectively) and showed the widest bathymetric ranges (Fig. 2). Seven genera showed large bathymetric ranges: Carbasea (31–2846 m), Austroflustra and Cornucopina (5–2700 m), Cellarinella (5–2334 m), Isosecuriflustra (22–2315 m), Kymella (0–2157 m) and Nematoflustra (0–2100 m). Four genera (15 species) were present at depths between 0 and 700 m. Bathymetric distribution Low stress values (0.03) of the MDS indicate a good representation in the 2-dimensional ordination (Clarke, 1993). Five depth zones were discriminated by the multidimensional scaling analysis in bathymetric distribution (Fig. 3): (1) a zone between 0 and 100 m with the presence of three Fig. 3. Plot of the multidimensional scaling ordination (MDS) of the different genera in relation to depth. Points numbered 100–5000 correspond to different depth ranges (stress = 0.03). Additional data have been obtained from Hayward (1981, 1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006) and Barnes & Kuklinski (2010). Group 1: 0–100 m; group 2: 100–700 m; group 3: 700–2000 m; group 4: 2000–3000 m and group 5: 3000– 5000 m. Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Table 2. Bathymetric ranges and biogeographic distribution of the species studied using data from the present study, the literature and the GBIF database. Species Carbasea curva Kluge, 1914 Klugeflustra antarctica Hastings, 1943 Isosecuriflustra angusta Kluge, 1914 Isosecuriflustra tenuis Kluge, 1914 Austroflustra vulgaris Kluge, 1914 Present study Klugella echinata Kluge, 1914 Notoplites antarcticus Waters, 1904 Notoplites drygalskii Kluge, 1914 170–640 104–634 123–1030 Weddell Sea Weddell Sea Weddell Sea Cellaria aurorae Livingstone, 1928 5–2334 Weddell Sea 5–3545 10–4531 123–668∗ (previously 634) 5–2700 5–528 0–4802 Weddell Sea Weddell Sea Weddell Sea Weddell Sea Deception Weddell Sea 118–1133 11–2334 5–1517 5–1517 61–1133 18–1495 Weddell Sea Weddell Sea Weddell Sea Weddell Sea Weddell Sea Weddell Sea 5–759 181–1404 0–2157 Weddell Sea Weddell Sea Weddell Sea 5–1150 35–628 Weddell Sea Weddell Sea Cellaria diversa Livingstone, 1928 Cellaria moniliorata Rogick, 1956d Cellaria incula Hayward and Ryland, 1993 Paracellaria wandeli Calvet, 1909 Melicerita latilaminata Rogick, 1956d Melicerita obliqua Thornely, 1924 Cellarinella nodulata Waters, 1904 Cellarinella nutti Rogick, 1956d Cellarinella rogickae Moyano, 1965 Cellarinella watersi Calvet, 1909 Systenopora contracta Waters, 1904 Isoschizoporella secunda Hayward and Taylor, 1984 Isoschizoporella tricuspis Calvet, 1909 Dakariella dabrowni Rogick, 1956d Kymella polaris Waters, 1904 Smittina antarctica Waters, 1904 Smittoidea albula Hayward and Taylor, 1984 X X X X X X X X New records for species ∗∗ References Zabala et al. (1997); Gontar & Zabala (2000) Hayward (1995) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Arntz et al. (2006); Hayward (1995); Zabala et al. (1997); Gontar & Zalaba (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Arntz et al. (2006) Zabala et al. (1997); Gontar & Zabala (2000); Hayward (1995) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000); Barnes & Kuklinski (2010) Zabala et al. (1997); Gontar & Zabala (2000); Barnes et al. (2010) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Barnes et al. (2008) Zabala et al. (1997); Gontar & Zabala (2000); Barnes & Kuklinski (2010) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000)) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Spatial patterns and diversity of bryozoan communities 0–2100 5–720 5–5900 20–294∗ (previously 293) 5–2000 5–2700 5–1517 X X 31–2846 5–732 31–2315 22–639∗ (previously 634) 5–2700 Geographic distr. Weddell Sea Livingston Weddell Sea Weddell Sea Bouvet Island, Livingston, Weddell Sea Weddell Sea Weddell Sea Weddell Sea Weddell Sea Weddell Sea Bouvet Island Weddell Sea, Livingston Nematoflustra flagellata Waters, 1904 Camptoplites angustus Kluge, 1914 Camptoplites bicornis Busk, 1884 Camptoplites giganteus Kluge, 1914 Camptoplites tricornis Waters, 1904 Cornucopina polymorpha Kluge, 1914 Himantozoum antarcticum Calvet, 1909 X X Bathymetric distr. (m) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000); Barnes & Kuklinski (2010) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) (Continued on next page) 115 Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 116 Table 2. (Continued) Species X X X Bathymetric distr. (m) Geographic distr. Weddell Sea Weddell Sea Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) 0–1150 56–616∗ (previously 567) 104–1150 Weddell Sea Weddell Sea Weddell Sea Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000); Barnes & Kuklinski (2010) 283–1543 61–622 86–1030 5–923 Spiess Seamount Weddell Sea Bouvet Island Weddell Sea X Reteporella hippocrepis Waters, 1904 X 61–634 Bouvet Island, Weddell Sea X 61–634 264∗ Weddell Sea Weddell Sea X 73–655 Weddell Sea Reteporella lepralioides Waters, 1904 Reteporella sp. nov. Figuerola, Ballesteros and Avila 2012 Alcyonidium unidentified species Kirkpatrick, 1902 ∗ New References 10–1517 10–732 Spigaleos horneroides Waters, 1904 Reteporella antarctica Waters, 1904 Reteporella erugata Hayward, 1992 Reteporella frigida Waters, 1904 X New records for species ∗∗∗ ∗∗ ∗∗∗∗ Zabala et al. (1997); Gontar & Zabala (2000) Arntz et al. (2006); Barnes et al. (2010) Zabala et al. (1997); Gontar & Zabala (2000); Barnes & Kuklinski (2010) Arntz et al. (2006); Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) Zabala et al. (1997); Gontar & Zabala (2000) bathymetric range described in this study, ∗∗ First record for Bouvet Island, ∗∗∗ First record for Spiess Seamount, ∗∗∗∗ First record for the Weddell Sea. B. Figuerola et al. Smittoidea ornatipectoralis Rogick, 1956d Thrypticocirrus contortuplicata Calvet, 1909 Pemmatoporella marginata Calvet, 1909 Bostrychopora dentata Waters, 1904 Osthimosia curtioscula Hayward, 1992 Present study Spatial patterns and diversity of bryozoan communities 117 Table 3. Number of species (no sps), per cent of relative species richness (% S) and P value (P) for each depth range in the Eastern Weddell Sea. Additional data have been obtained from Hayward (1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006) and Barnes & Kuklinski (2010). Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Depth (m) Fig. 4. Dendrogram from hierarchical clustering (single linkage) of the bryozoan fauna from the Southern oceans using Sørensen distance (Pearson cophenetic index 0.97). Additional data have been obtained from Hayward (1981, 1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006), Barnes et al. (2008) and Barnes & Kuklinski (2010). one depth interval (200–300 m), (3) a zone between 700 and 2000 m with a high similarity of generic composition but with fewer (nine) genera, (4) a zone between 2000 and 3000 m with the presence of four genera, and (5) another zone between 3000 and 5000 m characterized by the presence of M. obliqua only. Geographic distribution Cluster analyses suggested six principal groups of similar faunal composition (Fig. 4). The first group (1) is represented by the region of Eastern Weddell Sea comprised of the subregions of Kapp Norvegia (30 stations), Vestkapp (20 stations) and Austasen (32 stations) with the same number of species but of different composition. The islands of groups 3 and 4, the region of the Spiess Seamount (5) and the region of Neumayer (6) were represented by more separated groups with a lower number of species. In the results of tests for binomial proportions, the subregions of Kapp Norvegia with Austasen and Vestkapp showed no significant differences (P < 0.05). Deception Island, Livingston Island, Spiess Seamount and the Neumayer region showed significant differences with other regions (P < 0.05). Bouvet Island exhibited significant differences with respect to all other regions (P < 0.05). 100 200 300 400 500 600 700 800 900 1000 2000 3000 5000 no sps %S P 3 23 27 26 25 24 21 9 9 8 8 4 1 11.11 85.19 100.00 96.30 92.59 88.89 77.78 33.33 33.33 29.63 29.63 14.81 3.70 – 0.000 0.000 0.000 0.000 0.000 0.000 0.099 P > 0.1 P > 0.1 P > 0.1 P > 0.1 P > 0.1 The accumulation curve has still to reach the asymptote: 54 species have been found, but up to 90 (Chao2) can be expected as more samples are collected (Fig. 7). Jacknife1 and Jacknife2 methods estimated the theoretical number of expected species. These values are 82 and 97, respectively. However, in our case (absence of complete inventories), Chao2 has been shown to perform better than most other methods (Krebs, 1999). Five alpha diversity indices were calculated for each region only for the stations sampled with Agassiz trawl (AT), Bottom trawl (BT) and Rauschert dredge (RD) since they did not show significant differences (Table 4). The Shannon–Wiener and Margalef indices changed between regions with the highest value of indices and number of species in the region of Austasen (H’ = 3.445; DMg = 8.64), followed by Vestkapp (H’ = 2.844, DMg = 5,498), while Bouvet Island and Livingston Island showed low values Species richness and diversity indices Relative species richness (S) was low at depths between 0 and 100 m and from 800 to 5000 m, with significant differences between ranges from 100 to 700 m (test for binomial proportions, P < 0.01). The highest value was found between 300 and 400 m (Table 3; Fig. 5). The regions of Austasen, Kapp Norvegia and Vestkapp (with the same number of species but of different composition) had the highest species richness, followed by Bouvet and Deception Islands (Fig. 6). Fig. 5. Number of species (no sps) and per cent of relative species richness (% S) related to depth ranges in the Eastern Weddell Sea and the Antarctic Peninsula. Additional data have been obtained from Hayward (1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006) and Barnes & Kuklinski (2010). Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 118 B. Figuerola et al. Fig. 6. Number of species (no sps) and per cent of relative species richness (S) in different areas of the Eastern Weddell Sea and the Antarctic Peninsula. Additional data have been obtained from Hayward (1981, 1995), Zabala et al. (1997), Gontar & Zabala (2000), Arntz et al. (2006), Barnes et al. (2008) and Barnes & Kuklinski (2010). (Table 5). The diversity indices for Kapp Norvegia could not be calculated due to the unavailability of samples collected using these methods. Samples from Deception Island and Spiess Seamount contained only one species. to South America (43.75%) than to Antarctica (29.63%) (Table 6). Discussion Similarity with other regions In our study, the Antarctic region is connected by some genera shared with South America (55.5%), New Zealand (48.15%) and South Africa (37.04%). In fact, the South Shetland Islands had a composition slightly more similar Fig. 7. Sample-based rarefaction curve. Expected species richness value was computed with 95% confidence interval. The benthic fauna of the continental shelf of the Eastern Weddell Sea, as described for some other areas, is dominated by suspension feeders, such as bryozoans, and variations in their abundance are critical to the organization of the whole community (Teixidó et al., 2002, 2004). This shelf reaches great depths, with the shelf break at about 900–1000 m (Linse et al., 2006). Few bryozoan species have been reported from below the shelf break (Barnes & Kuklinski, 2010) and most benthic samples come from depths of less than 500 m (Griffiths, 2010). Antarctic bryozoans analysed here exhibit a high range of eurybathy. Bathymetric distributions of Antarctic fauna reported in the literature demonstrate that some species extend over large depth ranges (Brey et al., 1996; Soler i Membrives et al., 2009). Twenty-seven bryozoan species of this study have been recorded in the Southern Ocean deeper than 1000 m. The case of the genus Camptoplites is even more amazing, showing a depth range of 0–5900 m. The existence of eurybathic species has been explained by the evolutionary history of the Southern Ocean fauna (Munilla, 2001). Thatje and colleagues (2005) suggested that the impact of the grounded ice sheets on most of the Antarctic continental shelf during Cenozoic glacial periods affected the benthic communities. Therefore, the continental shelf was further recolonized by deep-water organisms with wide bathymetric tolerances and thus, depth seems to be a less important factor in controlling the Spatial patterns and diversity of bryozoan communities 119 Table 4. Diversity indices for the three types of sampling (AT: Agassiz trawl, BT: Bottom trawl and RD: Rauschert dredge) from the present study with 95% confidence intervals using Bootstrap method: Margalef index (DMg ), Shannon–Wiener diversity index, H’ (base log e), Simpson’s Index (1 – Lambda’), Pielou’s index (J’) and Berger–Parker index (B–P). H′ DMg Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 AT BT RD 1-Lambda′ J′ BP Lower Upper Lower Upper Lower Upper Lower Upper Lower Upper 5.87 6.16 5.11 8.21 8.44 7.67 3.01 3.05 2.82 3.40 3.41 3.27 0.93 0.94 0.92 0.96 0.96 0.96 0.72 0.71 0.74 0.87 0.85 0.90 0.07 0.08 0.08 0.17 0.16 0.20 distribution of communities compared with other areas. Changes in Antarctic biodiversity have been found to be associated with the movement of taxa between the shelf and the deep sea (Brey et al., 1996; Arntz et al., 1997; Brandt & Hilbig, 2004). However, this possibility has not been proved so far (Thatje et al., 2005). The possibility should also be considered that some deep occurrences (>1000 m) are due to transport off the shelf by currents, as shown for bryozoans from elsewhere, such as New Zealand (Lagaaij, 1973, Hayward, 1981; Taylor et al., 2004). Horizontal and vertical variability in Antarctic bryozoan distributions does exist. For some benthic species, horizontal and bathymetric distribution patterns have been described, but, in the case of most bryozoan species from this area, their horizontal distribution and bathymetric ranges are relatively unknown. Multidimensional scaling analysis in our study showed that bryozoans were distributed in zones or depth bands. Clarke et al. (2003) reported that in Antarctica the continental shelf lies at depths between 500 m and 700 m and in some places depths exceed 1000 m, while the continental slope is found at 1000–3000 m and the deep sea at over 3000 m. For example, Prydz Bay is considered to be Antarctic shelf with the deepest areas about 1200 m (O’Brien et al., 2007). The bryozoan distribution found in our study fits well with these proposed limits: the species composition of continental shelf (0–700 m or 800–1000 m) differs from that of the continental slope and of the deep sea (>3000 m). However, the sample effort banding may have influenced these results. In agreement with this, Kaiser and colleagues (2011) found that the shelf and abyssal bryozoans were clearly separated in the Weddell Sea. Some studies have demonstrated that Antarctic megafaunal density generally decreases with depth (Arntz et al., 1994; Thatje & Mutschke, 1999; Rex et al., 2006; Linse et al., 2007), which can be related to the decreasing availability of food with depth. However, other factors could be correlated with this, such as a limited availability of substratum for encrusting species at depth. Decrease in organic matter is considered to be the main limiting factor for the Antarctic benthos (Arntz et al., 1994; Lampitt et al., 2001; Saiz-Salinas et al., 2008). Barnes & Kuklinski (2010) also reported that the bryozoan species richness decreases rapidly with depth. Nevertheless, abundances are very variable at depths of 1000–3500 m and some authors have suggested the existence of patchy distribution patterns (Brandt et al., 2005). In agreement with this, slope richness of some taxa and of some areas was larger than that of the shelf or abyss zones (Kaiser et al., 2011). In contrast, other findings suggested that abundance increases with depth in some areas of the Weddell Sea and decreases with depth in other areas, such as Kapp Norvegia (Linse et al., 2002). In addition, there are other factors we must take into account, such as biological factors (e.g. food availability and predation), which may have more influence at small spatial scales and depths greater than 20 m, where physical distur- Table 5. Characteristics of the regions sampled with the three dominant types of sampling (AT, BT and RD). For each region: dominant species found in the sample, total number of species found (no sps), Margalef index (DMg ), Shannon–Wiener diversity index, H’ (base log e), Simpson’s Index (1 – Lambda’), Pielou’s index (J’) and Berger–Parker index (B–P). Site Dominant species found in the sample Bouvet Island Austasen Vestkapp Osthimosia curtioscula Bostrychopora dentata Carbasea curva Nematoflustra flagellata Spigaleos horneroides Austroflustra vulgaris Himantozoum antarcticum Klugeflustra antarctica Melicerita latilaminata Spiess Seamount Livingston Island Deception Island no sps DMg H′ 1-Lambda′ J′ B-P 13 145 38 1.559 8.64 5.498 1.525 3.445 2.844 0.7692 0.9557 0.9294 0.9188 0.7124 0.8186 0.3077 0.1241 0.1316 1 3 0 1.82 0 1.099 0 0.6667 1 1 1 0.3333 1 0 0 0 1 1 120 B. Figuerola et al. Table 6. Genera found in this study in Antarctica and Scotia Arc. Additional data from South America, New Zealand and South Africa have been obtained from Moyano (1982, 1999), Gordon (1984, 1986), Florence et al. (2007); see also www.bryozoa.net. Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Genera Carbasea Klugeflustra Isosecuriflustra Austroflustra Nematoflustra Camptoplites Cornucopina Himantozoum Klugella Notoplites Cellaria Paracellaria Melicerita Cellarinella Systenopora Isoschizoporella Dakariella Kymella Smittina Smittoidea Thrypticocirrus Pemmatoporella Bostrychopora Osthimosia Spigaleos Reteporella Alcyonidium South New South Scotia Antarctica America Zealand Africa Arc x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x bance by ice is less frequent. With this regard, Smale (2008) found high variability in the distribution of species in these conditions. The result of our cluster analyses indicated a spatial pattern in the distribution of species of bryozoans, and the different regions observed agree with the different zoogeographical zones of diversity suggested by previous authors (Barnes & De Grave, 2000; Barnes & Kuklinski, 2010): the Sub-Antarctic islands (Bouvet Island), East Antarctica (eastern Weddell Sea), West Antarctica and the Scotia Arc (Deception and Livingston Islands). At a smaller scale, we observed a horizontal variability in assemblage composition between some regions. The regions of Kapp Norvegia (30 stations), Vestkapp (20 stations) and Austasen (32 stations) showed the same values of relative species richness. However, the regions of Kapp Norvegia and Vestkapp are more similar (the subgroup of cluster 1 has the highest similarity, 92%), indicating an even greater similarity in species composition. The reason for this similarity could be their proximity. Moreover, Gerdes et al. (2008) proposed that the shelf off Austasen has to be considered as a patchwork of disturbed areas and this could be the reason for its higher diversity (higher values of DMg , H’ and 1-Lambda’ indices) compared with Vestkapp. In contrast, the value of the Berger–Parker and Pielou’s indices were lower because there were many individuals of one species (B. dentata). However, this area shows the same value of species richness as the region of Kapp Norvegia (84% similarity). The regions of Neumayer, the Spiess Seamount and the islands of Bouvet, Deception and Livingston are separated geographically, and exhibit the lowest species richness and diversity because they are distant from other regions and scarcely sampled. Many new records of known or unknown species can be expected to be found in the future. Also, the rarefaction curve showed no sign of approaching an asymptote. Fifty-four species have been found, but total numbers estimated by species richness statistics (Chao2) suggest that at least 90 species of bryozoans will be found in the studied area as more samples are collected. Some studies have reported that Bouvet Island shows similarity with the region of the Weddell Sea and has a similar taxonomic richness (Barnes, 2006; Gutt et al., 2006) and our results for bryozoans are in agreement with that. This could be due to the existence of a permanent import of species by dispersion of marine benthic animals (Pielou, 1975). Other studies have demonstrated that the general composition and diversity of Bouvet Island were not lower compared with the Patagonian shelf and only moderately lower than the Antarctic continental shelf (Arntz et al., 2006; Gutt et al., 2006). Bouvet Island and the region of Spiess Seamount are located at a particular position relative to the Antarctic Circumpolar Current and may be in a potential zone of faunal exchange among the various regions and across the Polar Front (Linse, 2006). Larvae of different invertebrates from the Scotia Arc could reach Bouvet Island with the Circumpolar Current or from the Weddell Sea with the Weddell Gyre (Barnes, 2006). One hypothesis is that Bouvet Island could have acted as a supply source to the Weddell Sea during the glacial maximum, when this island was not covered by ice and adults of species could travel on kelp or pumice with currents of the Weddell Sea Gyre (Barnes & Kuklinski, 2010). The benthos of the Spiess Seamount is characterized by being extremely poor (Arntz et al., 2006). However, the cluster analyses showed Deception Island to be more separated than the other islands (0% of similarity). San Vicente et al. (1997) suggested that the reduced number of species at Deception Island was probably related to the last volcanic episode and to the present acidity in the surface sediment. This could also explain the low bryozoan diversity. Also, the availability of hard substrates limits the abundance and diversity of bryozoans (Hughes, 2001). Many filter feeders have a preference for an elevated position which may enhance prey capture (Wildish & Kristmanson, 1997). Deception Island has few hard substrates and this could affect bryozoan diversity. However, Barnes et al. (2008) reported that the undersurfaces of boulders from Deception Island are dominated by bryozoans (cryptofauna). Downloaded by [University of Barcelona], [Blanca Figuerola] at 10:09 27 March 2012 Spatial patterns and diversity of bryozoan communities The presence of a common bryozoan fauna between South America and the Western Antarctica can be explained by their proximity during the Tertiary (Zinsmeister, 1979) and by the relatively similar environmental conditions related to the Antarctic Circumpolar Current (Moyano, 1982). Various studies support the role of the Scotia Arc as the link between Antarctica and South America (e.g. Arntz et al., 2005). In our study, the South Shetland Islands showed a balanced composition between these two regions, thus supporting this hypothesis. Although Antarctic endemism is very high, zoogeographically, there are clear relationships between the fauna of Antarctica and those of South America, New Zealand and South Africa. These similarities could be traced back to the time when continents were part of Gondwana. Also, in the Oligocene, a palaeobiogeographic connection between New Zealand and Patagonia may have existed, as shown by the presence of common taxa, through the West Antarctic Rift System (Casadı́o et al., 2010). In Antarctica, a clear latitudinal cline in diversity, oriented north to south along the western Antarctic Peninsula, has been reported also for macroalgae and molluscs (Moe & deLaca, 1976; Schiaparelli et al., 2006). The existence of a similar cline in bryozoan diversity has been found in this study, with a higher richness at 70–73◦ S (Austasen, Kapp Norvegia and Vestkap) than at 54–70◦ S (Bouvet, Livingston and Deception Islands, and Neumayer). However, the interpretation of these results must be treated with some caution because they are based on the frequency of occurrence rather than the abundance of species. Conclusions During the past two decades, research of the basic descriptive taxonomy and benthic ecology from the Southern Ocean has improved greatly, demonstrating that this area is quite rich and diverse. However, some almost inaccessible regions, such as some parts of Antarctica, are difficult to sample and the research on biodiversity is limited by the lack of richness data for some groups, such as the bryozoans. Although the results of the analyses performed here from new data on bryozoan biodiversity increase our knowledge of species’ geographical ranges, they are still limited because samples were collected from only a few areas. The scales of the latitudinal and the bathymetric gradients are large and the majority of marine studies have only sampled small areas. This causes an underestimation of diversity because it has been demonstrated that species richness varies with increasing sampled area (Gray, 2000). The main limitation of this study is the use of data from different methods of sampling. However, the bathymetric and geographical distributions of the studied species contribute to a better understanding of Antarctic bryozoan diversity and distributions and it is relevant in the establishment of biogeographical patterns. More intensive sampling of bry- 121 ozoans along a wider geographical range is needed for the Weddell Sea and other Antarctic areas. Acknowledgements The authors wish to thank Dr C. López Fé de la Cuadra (University of Sevilla) for his help in the identification of some species and Dr D. P. Gordon (National Institute of Water and Atmospheric Research), Dr M. Zabala (University of Barcelona) and Dr B. Berning (Linz Museum, Austria) for their help with bibliographic searches. Special thanks go to S. Taboada, J. Vázquez, L. Núñez-Pons and F.J. Cristobo for laboratory support and to Dr R. Sardà and Dr A. Maceda for their reviews of the manuscript. Thanks are due to W. Arntz and the crew of the R/V of Polarstern (AWI) for inviting us to participate in the Antarctic cruise ANT XXI/2 (AWI, Bremerhaven, Germany), and M. Franch for helping with the maps. Funding was provided by the Ministry of Science and Education of Spain through the ECOQUIM and ACTIQUIM Projects (REN2002-12006EANT, REN200300545, CGL2004-03356/ANT and CGL2007-65453). References ARNTZ, W.E. & BREY, T. 2005. The expedition ANTARKTIS XXI/2 (BENDEX) of RV “Polarstern” in 2003/2004. Berichte zur Polarforschung/Reports on Polar Research 503, 31–35. ARNTZ, W.E., BREY, T. & GALLARDO, V.A. 1994. Antarctic zoobenthos. Oceanography and Marine Biology, Annual Review 32, 241–304. ARNTZ, W.E. & GUTT, J. 1997. The expedition ANTARKTIS XIII/3 (EASIZ I) of “Polarstern” to the eastern Weddell Sea in 1996. Berichte zur Polarforschung/Reports on Polar Research 249, 1–148. ARNTZ, W.E., LOVRICH, G.A. & THATJE, S. 2005. The Magellan–Antarctic connection: links and frontiers at high southern latitudes. 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