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 manne nematode coinmunities in the high Antarctic. Our attempt at surveying this n~unerically most abundant meiobenthic taxon along the continental shelf and slope (200 to 2000 m) furmshed 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 muted habitat consisting of shelf break and Kapp Norvegia shelf. Dominated by genera like Sabatiena, Molgolaimus, A4icrolalmus, Monhystera, Daptonema, Leptolaimus, Acantholaimus and Dichromadora, these habitats often contained distinct associations of less abundant genera. The trophically diverse communities exhibited an equal shanng of epistrate, nonselective and selective deposit feeders, with a slight dominance of the flrst feedlng 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. Globalscale compaiisons with literature data indicated the broad geographical distnbution of predominant nematode taxa and a lack of Antarctic endermsm. 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.

Broad-scale patterns in local diversity of marine benthic harpacticoid copepods (Crustacea)

“…For example, compilation of the published data did not reveal any prominent latitudinal gradients for shallow water free-living marine nematodes in the southern hemisphere, whereas the samples collected specifically along the coast of Chile between 18 and 42°S showed that sandy beach nematode fauna follows the classic latitudinal gradient (Boucher 1990, Lee & Riveros 2011. The wider inter-regional comparisons, however, did not show obvious latitudinal trends in nematode α diversity, in contrast to macrofauna (Vanhove et al 1999, Mokievsky & Azovsky 2002, Muthumbi et al 2004). Harpacticoids, aside from nematodes, are ubiquitous and often the most abundant component of marine meiofauna (Giere 2009).…”

“…Several inter-regional comparisons of nematode α diversity, using various diversity indices, found no obvious latitudinal trends, in contrast to macrofauna (Vanhove et al 1999, Mo kievsky & Azovsky 2002, Muthumbi et al 2004. Changes in deep-sea nematode assemblages along bathymetrical gradients prevail over latitudinal gradients and references therein, Fonseca et al 2010).…”

“…A nonlinear (unimodal) diversity−depth relationship is generally considered as the common pattern that has been reported for both macrobenthos (bivalves, gastropods, amphipod crustaceans, and other groups; Stuart et al 2003, McClain et al 2009, Renaud et al 2009, and references therein) and meiobenthos (nematodes and harpacticoids; Vanhove et al 1999, Lambshead & Boucher 2003, Muthumbi et al 2004, Baguley et al 2006, although the depth of peak diversity varies tremendously among taxa and basins. Explanations of this unimodal pattern are many, involving complex interactions among productivity, disturbance regime, speciation rates, habitat heterogeneity, and patch dynamics, all of which are related to depth.…”

“…It is unclear whether these differences are caused by regional peculiarities or by the restricted geographical range of stations sampled (Renaud et al 2009). Furthermore, regional diversity shows consistently stronger and steeper latitudinal gradients than local (α) diversity (Clarke & Lidgard 2000, Hillebrand 2004, thus posing the question of systematic variation in β diversity (see below).A nonlinear (unimodal) diversity−depth relationship is generally considered as the common pattern that has been reported for both macrobenthos (bivalves, gastropods, amphipod crustaceans, and other groups; Stuart et al 2003, McClain et al 2009, Renaud et al 2009, and references therein) and meiobenthos (nematodes and harpacticoids; Vanhove et al 1999, Lambshead & Boucher 2003, Muthumbi et al 2004, Baguley et al 2006, although the depth of peak diversity varies tremendously among taxa and basins. Explanations of this unimodal pattern are many, involving complex interactions among productivity, disturbance regime, speciation rates, habitat heterogeneity, and patch dynamics, all of which are related to depth.…”

From microbes to macrofauna: an integrated study of deep benthic communities and their response to environmental variables along the Malta Escarpment (Ionian Sea)

“…Hasemann and Soltwedel (2011) inferred that factors that influence the nematode community have different effects in different areas. Vanhove et al (1999) underlined that the spatial variability of the meiofauna and the different aggregations are related to different groups of factors (i.e. physical, chemical and biological) that can act together on meiobenthic communities.…”