Original paper

Temporal variations in epilithic nematode assemblages in lakes of different productivities

Schroeder, Fabian; Peters, Lars; Traunspurger, Walter

Abstract

The aim of the present study was to examine: (1) the response of nematodes to temporal changes in the periphyton of stony hard-substrates (epilithon) and (2) the distribution of the nematode species among lakes of different productivities. Accordingly, epilithic nematode assemblages of three Swedish lakes with different trophic states were analyzed over a 2-year period. Depending on habitat size and food availability measured as organic material, algal biomass and inorganic material, nematode populations showed distinct temporal patterns, reaching maximum densities up to 1014 ind. cm-2 in spring and lowest densities in winter (minimum abundance 27 ind. cm-2). A comparison of the analyzed lakes revealed clear differences in nematode species composition. A multivariate statistical analysis showed that the distribution of nematode species along the lakes was significantly linked to the nutrient conditions of the lakes and to the algal biomass in the epilithon. Accordingly, several nematode species could be classified as bioindicators of lake trophic state. Whereas, for example, the two dominant algal-feeding species, Punctodora ratzeburgensis and Chromadorina viridis, were dependent on high nutrient levels, the abundance of species belonging to the genera Rhabdolaimus (R. aquaticus, R. terrestris) and Eumonhystera (E. vulgaris, E. simplex, E. pseudobulbosa) correlated negatively with trophic state. Also linked to increasing nutrient conditions was the change in the composition of the nematode feeding types among the lakes, from one dominated by bacterial feeders to one in which algal feeders predominated. The trophic structure of the assemblage changed in parallel, with a larger proportion of predatory species (chewers) in the eutrophic lake than in the two lakes which were more nutrient poor. For suction feeders, the inverse pattern was observed. Our results underline the importance of the epilithon as the habitat of a highly abundant and diverse nematode fauna that is strongly influenced by the trophic state of its resident lake.

Keywords

meiofaunanematodesperiphytonfeeding typestrophic state