Abstract
Megabenthic epifauna composition and distribution from the Scotia Arc islands based on data collected during the Antarctic summer of 1986-87 is presented. Samples were taken from bottom trawl catches at 345 stations (29 at Shag Rocks, 104 at South Georgia, 8 at the South Sandwich Islands, 93 at the South Orkney Islands, 46 at Elephant Island, and 65 at the South Shetland Islands), from 26 to 643 m depth. Among the most striking features of the faunistic composition of the area, pointed out by multivariate analysis, are the singularity of Shag Rocks, closer to the Magellan region, and of the volcanic South Sandwich Islands, as well as the similarity of South Georgia and the South Orkney Islands and that of the islands nearest to the Antarctic continent, especially Elephant Island and the South Shetlands Islands. This similarity is due to the higher frequency and abundance of the most characteristic taxa in the Antarctic epibenthos, such as sessile suspension feeders (sponges, calcareous bryozoans, pennatulids, crinoids), and motile fauna with a wide variety of trophic strategies (asteroids, holothurians, pycnogonids, large isopods and gammarids). These data confirm the fact that the long-lived suspension-feeder communities, demosponges and hexactinellids, characteristic of the Antarctic epibenthos stretch to the eastern shelf of South Georgia without reaching the north-west of this island, the South Sandwich Islands, and Shag Rocks. Some of the zones with rich communities of sessile filter-feeders, long-lived sponges or reef formations of calcareous bryozoans or serpulids should be proposed as Specially Protected Areas.
Highlights
It is known that until the mid-Cretaceous, the South Georgia shelf remained directly linked to South America (Dalziel, 1983; Headland, 1984) and the South Orkneys were still attached to the Antarctic Peninsula (Dalziel, 1983)
The Scotia Arc would constitute a pathway for species exchange between the Subantarctic and Antarctic regions (Picken, 1985), which would have kept the benthic Antarctic ecosystem from total isolation
Suspension feeders were represented by colonial cnidarians, dominant in two very restricted western areas
Summary
The Scotia Arc, a series of trenches and elevations spreading over more than 1,500 km between the south-ern tip of South America and the Antarctic Peninsula (Acosta et al, 1989) constitutes a important area for understanding the history of the Southern Ocean marine fauna (Clarke and Crame, 1989).It is difficult to establish a detailed geological history of the Scotia Arc (Clarke and Crame, 1989).it is known that until the mid-Cretaceous, the South Georgia shelf remained directly linked to South America (Dalziel, 1983; Headland, 1984) and the South Orkneys were still attached to the Antarctic Peninsula (Dalziel, 1983). The Scotia Arc would constitute a pathway for species exchange between the Subantarctic and Antarctic regions (Picken, 1985), which would have kept the benthic Antarctic ecosystem from total isolation. This hypothesis remains unproven (Dayton, 1990) and the current oceanographic situation, with the Convergence barrier and the limited dispersal ability of many forms, makes it likely that exchange is very slow (Clarke and Crame, 1989)
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