C Primo

Zoogeography of the Antarctic ascidian fauna in relation to the sub-Antarctic and South America

Abstract This study of the relationships between the Antarctic, sub-Antarctic and South America biogeographical regions used both existing and new data. We constructed a presence/absence matrix of 237 species for 27 biogeographical divisions which included the Amsterdam-Saint Paul and Tristan da Cunha islands. Species and areas were classified using cluster analysis combined with MDS ordination. Six main groups were obtained from the species classification: 1) Amsterdam-Saint Paul, and 2) Tristan da Cunha species, 3) species from the Macquarie Province, 4) species from the sub-Antarctic Region, 5) Antarctic species and species distributed in the cold regions, 6) South American species. The biogeographical components were dominated by the endemic (although it is not as high as in other groups), Antarctic-South America and Southern Hemisphere elements. Except for Amsterdam-Saint Paul, Tristan da Cunha and Bouvet, the areas considered were grouped together with Macquarie being rather related to New Zealand regions. We speculate that the Antarctic Region may have acted as an “evolutionary incubator”, providing a centre of origin for sub-Antarctic and South American ascidians.

Antarctic ascidians: an isolated and homogeneous fauna

Several biogeographical studies have already been performed on the ascidians of the Antarctic region. However, new data obtained in the last few years have led us to a revision of the biogeography of this fauna. To examine the biogeographical structure of the Antarctic region, we divided it into 10 sectors, depending on the principal geographical features, and then applied cluster analysis and a multi-dimensional scaling ordination to a presence/absence matrix of species for each biogeographical area. Our study shows that Antarctic ascidians are a very homogeneous fauna, with a high level of endemism in the whole region (25–51% of Antarctic endemic species per sector), but with a low percentage of sector endemism (only up to 10%). This probably results from isolation arising from the Antarctic Convergence, and the vast geographical distances from adjacent regions, as well as from the relative constancy of the hydrographical conditions and the dispersal of organisms through circumpolar currents. In fact, cosmopolitan species represented only 0–7% of the total ascidian fauna in all sectors. Only the Bellingshausen Sea (low sample size), Bouvetøya (young and isolated, with an impoverished ascidian fauna) and the South Sandwich Islands (also young and isolated) are relatively separated. The insular sectors were more closely related to the South America and sub-Antarctic regions than the continental ones, showing a latitudinal gradient.

Zoogeography of the southern New Zealand, Tasmanian and southern African ascidian fauna

Abstract We studied the relationships among the ascidian fauna of southern New Zealand, Tasmania, and southern Africa, considering main currents and surface water temperature. We constructed a presence/absence matrix of 494 ascidian species from these regions (which were also divided into provinces) for 28 biogeographical worldwide regions using published records. Biogeographical areas were classified using cluster analysis combined with non‐metric multidimensional scaling ordination. The region classification separated Vema Seamount because of the low number of citations and the high number of ascidian endemism owing to an island effect. The Tasmanian, southern African and southern New Zealand regions formed separate groups. The ascidian fauna was dominated by endemic species in southern New Zealand (43%) and southern Africa (45%), whereas southern Australian species dominated the Tasmanian fauna (41%).

Ascidians collected during the Spanish Antarctic expedition CIEMAR 99/00 in the Bransfield and Gerlache Straits

During the Spanish expedition CIEMAR 99/00, on board the BIO‐Hespérides, 30 species of ascidians (distributed in 13 genera and eight families) were collected using a rock dredge in the Bransfield and Gerlache straits. Most of them were already known, but one species, Tetrazona ciemari sp. nov., is new for science. Additional morphological data are provided for six species. Five are reported for only the second time and the known distributions of five species are extended.