Sponge assemblages of the deep Weddell Sea: ecological and zoogeographic results of ANDEEP I–III and SYSTCO I expeditions

Abstract

The aim of this study is to analyze the community structure, ecology and distribution of deep Weddell Sea sponge faunas. Analysis was performed on the basis of sponges sampled during ANDEEP I–III and SYSTCO I expeditions (2002–2008) by RV Polarstern. The material obtained comprises about 800 sponge specimens, representing 129 species, within these are 95 species of demosponges (including 15 new to science), 25 hexactinellid species (7 new) and 9 calcarean species (5 new). Sponges were sampled at 51 stations in depths between 500 and 5,500 m. At most stations, sponge densities were very low, and many species are represented by one or two specimens only. Community structure by Bray–Curtis similarity was analyzed as well as depth range and spatial distribution of the most common species. Zoogeographic affinities of sampled faunas are analyzed. Three associations of sponges are found in the deep Weddell Sea: (1) The Polymastia/Tentorium community, (including Rossella associations) distributed on the lower shelf and continental slope. (2) The Bathydorus community, distributed on the continental slope and upper abyssal. (3) The Caulophacus community, associated with Cladorhizidae, is characteristic for the abyssal plains. The associations follow each other successively both bathymetrically and geographically, from shallow to deep, from shelf and ridge structures into the open abyssal. A distinct faunistic boundary between shelf and deep sea is not present. In general, the sponge fauna of the deep Weddell Sea is regionally restricted and shows stronger affinities only to the sponge fauna of the subantarctic islands.