Comparative study of the nematode communities on the southeastern Weddell Sea shelf and slope (Antarctica)

Nothing is known about the structure of free-living marine nematode communi ties in the high Antarctic. Our attempt at surveying this numerically most abundant meiobenthic taxon along the continental shelf and slope (200 to 20 00 m) furnished information on generic, trophic and age composition in 2 re gions in the Weddell Sea (Kapp Norvegia, 6 stations, 71-72 degrees S, 12-13 degrees W; Halley Bay, 11 stations, 74-75 degrees S, 25-29 degrees W). A t otal of 7300 nematode identifications to generic level were analyzed by mea ns of a variety of statistical techniques. The spatial structure indicated the existence of 4 major nematode genus associations colonizing the upper s lope, downslope, Halley shelf and a mixed habitat consisting of shelf break and Kapp Norvegia shelf. Dominated by genera like Sabatieria, Molgolaimus, Microlaimus, Monhystera, Daptonema, Leptolaimus, Acantholaimus and Dichrom adora, these habitats often contained distinct associations of less abundan t genera. The trophically diverse communities exhibited an equal sharing of epistrate, nonselective and selective deposit feeders, with a slight domin ance of the first feeding category. Each feeding guild was considered in Li ght of the correlations with microbial food and fresh versus decomposing or ganic matter, leading to the conclusion that the applied classification doe s not adequately explain the trophic status of the deep-water communities. Global-scale comparisons with literature data indicated the broad geographi cal distribution of predominant nematode taxa and a lack of Antarctic endem ism. Only a weak separation of the entire nematode communities on a geograp hical basis was suggested by multivariate techniques. Although ocean-wide c omparison was hampered by limited comparable literature data, diversity ind ices scored high and surpassed the Arctic bathyal assemblage. The major age nts behind the observed patterns involved sediment grain size and food cont ent, operating over different scales. Depth per se had no major effect. Und erlying mechanisms included water-column productivity, hydrodynamics, icebe rg activity and macrofaunal presence.