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

Abstract

Nothing is known about the structure of free-living marine nematode communities in the high Antarctic. Our attempt at surveying this numerically most abundant meiobenthic taxon along the continental shelf and slope (200 to 2000 m) furnished information on generic, trophic and age composition in 2 regions in the Weddell Sea (Kapp Norvegia, 6 stations, 71-72°S, 12-13°W; Halley Bay, 11 stations, 74-75°S, 25-29°W). A total of 7300 nematode identifications to generic level were analyzed by means of a variety of statistical techniques. The spatial structure indicated the existence of 4 major nematode genus associations colonizing the upper slope, 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 Dichromadora, these habitats often contained distinct associations of less abundant genera. The trophically diverse communities exhibited an equal sharing of epistrate, nonselective and selective deposit feeders, with a slight dominance of the first feeding category. Each feeding guild was considered in light of the correlations with microbial food and fresh versus decomposing organic matter, leading to the conclusion that the applied classification does not adequately explain the trophic status of the deep-water communities. Global-scale comparisons with literature data indicated the broad geographical distribution of predominant nematode taxa and a lack of Antarctic endemism. Only a weak separation of the entire nematode communities on a geographical basis was suggested by multivariate techniques. Although ocean-wide comparison was hampered by limited comparable literature data, diversity indices scored high and surpassed the Arctic bathyal assemblage. The major agents behind the observed patterns involved sediment grain size and food content, operating over different scales. Depth per se had no major effect. Underlying mechanisms included water-column productivity, hydrodynamics, iceberg activity and macrofaunal presence.