RESEARCH ARTICLE J. M. Ragua´-Gil Æ J. Gutt Æ A. Clarke Æ W. E. Arntz Antarctic shallow-water mega-epibenthos: shaped by circumpolar dispersion or local conditions? Received: 7 March 2003 / Accepted: 6 November 2003 / Published online: 30 January 2004 Ó Springer-Verlag 2004 Abstract The mega-epibenthos of two different geo- graphic areas, the Antarctic Peninsula and the high Antarctic (eastern Weddell Sea), were investigated using underwater video. The distribution of the marine fauna at shallow depths between 55 and 160 m in these two areas was investigated to determine whether there are any zoogeographic differences at the community level. A total of 237 taxa represented by 85,538 individuals was identified. Multivariate analyses revealed significant faunal differences between northern Marguerite Bay (western Antarctic Peninsula) and the stations from the Weddell Sea, Atka Bay and Four-Seasons Bank. Echi- noderms, especially ophiuroids, dominated Marguerite Bay, bryozoans and ascidians were abundant at Atka Bay, and hydroids and gorgonians were well represented at Four-Seasons Bank. These clear differences can mainly be explained by the influence of local environ- mental conditions that are probably the primary feature responsible in shaping the Antarctic shallow-water epi- fauna and not an intensive exchange with larger depths or a limited dispersion due to scarce and isolated shallow areas. In addition, modes of reproduction and charac- teristics of the early life history (e.g. brooding, viviparity or budding) of key taxa may also shape patterns of species distribution in shallow benthic Antarctic com- munities. Introduction The origin and evolution of Antarctic benthic fauna have long been discussed in the literature (Lipps and Hickman1982; Clarke and Crame 1989, 1992, 1997). The fauna of the Antarctic Peninsula and of the high-Ant- arctic Weddell Sea have long been considered to belong to different zoogeographical regions (Hedgpeth 1971). These two areas separated from each other by ca. 2,160 km, are characterised by strong seasonality, with changing light regimes, ice coverage (Gutt 2000), pri- mary production, sedimentation (Arntz et al. 1992), but relatively constant physical conditions (Klages 1993; Klages et al. 1995). However, these two regions differ in one striking aspect that is generally relevant to the benthos, namely, that the Antarctic Peninsula has a true coast and, thus, true littoral areas are common. In contrast, >95% of the coastline and near-shore region of the high-Antarctic is covered by floating or grounded ice; thus, deep waters (>150 m) predominate and con- sequently shallow areas are scarce (Drewry 1983; Gutt 2000). In the Weddell Sea, two shallow sites with water depths between 55 and 160 m are known: the inner parts of Atka Bay and a recently discovered shallow bank off Four-Seasons Inlet north-east of Kapp Norvegia. This bank seems to host a faunal assemblage, which differs from that of the well-investigated, adjacent, deeper wa- ters. With this background, the current study centred around the following hypotheses and questions: 1. On all continents other than Antarctica, animals re- stricted to shallow waters can disperse continuously along shelves over long distances. Around Antarctica littoral areas not covered by ice-shelf are scarce and highly isolated. Can this condition cause a permanent reduction in the dispersion of the shallow-water species, or does a circumpolar, relatively homoge- nous, shallow-water fauna exist? Are general con- clusions on the role of bridging long distances possible for macrobenthic species? Communicated by O. Kinne, Oldendorf/Luhe J. M. Ragua´-Gil (&) Æ J. Gutt Æ W. E. Arntz Alfred-Wegener-Institute fu¨r Polar- und Meeresforschung, Columbusstraße, 27568 Bremerhaven, Germany E-mail: jragua@awi-bremerhaven.de A. Clarke British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK Marine Biology (2004) 144: 829–839 DOI 10.1007/s00227-003-1269-3