Effects of copepods and chironomids on the abundance and vertical distribution of nematodes in a freshwater sediment

In the presence of copepods and chironomids the number of nematodes in a laboratory microcosm system was not influenced; however, the vertical distribution patterns in the sediment were influenced by the presence or absence of copepods and chironomids. The relative numbers of nematodes in 0-1 cm versus 1-5 cm sediment layer in copepod and copepod plus chironomid treatments were significantly higher than that for the controls. The vertical distribution of three dominant nematode species (Eumonhystera filiformis, Ethmolaimus pratensis and Tobrilus sp.) showed that the juveniles were more concentrated in the superficial sediment layer, whereas adults burrowed deeper into the sediment. Significant differences for the vertical distribution were found for adults of E pratensis and for juveniles of E filiformis and E. pratensis. Analysis of the macro- and meiozoobenthos of Lake Starnberger See indicated that nematode abundances were positively correlated with those of chironomids, oligochaetes, ostracods, and copepods.