Free-living, non-parasitic nematodes are the most abundant and one of the species-richest metazoans in sediments and soils and are major contributors to important ecosystem services (Yeates, 1981; Ferris et al., 2001; Traunspurger 2000, 2002).
With the evolution of several different feeding types, nematodes have successfully occupied key positions in terrestrial and benthic food webs (Yeates et al., 1993, Traunspurger 1997a), influencing nutrient cycling in soils (Ingham et al., 1985; Beare, 1997; Traunspurger et al. 1997b).
The presence of nematodes and the structure of nematode communities are important to agricultural production and sustainability (Fiscus and Neher, 2002).
Moreover, nematodes are suitable indicators for assessing pollution in soils and freshwater sediments (Bongers, 1990; Danovaro et al. 2009; Nagy, 2009; Zhao and Neher, 2013; Höss et al., 2011a, b). For effect assessment there exist test systems at all organizational and ecological levels: from molecular markers, to single-species tests, model ecosystems and community indices for bioindication (see Fig. 2).
Nematodes are especially useful for small-scale experimental setups, due to their exceptionally high abundances. Thus, already in a few gram of soil or sediment, there are already enough organisms to analyze the structure of a nematode assemblage, following statistically sound criteria.