INTERACTIONS BETWEEN EARTHWORMS AND SOIL PROTOZOA - A TROPHIC COMPONENT IN THE SOIL FOOD-WEB

Earthworms and protozoa are, in terms of biomass, the most important g roups of soil fauna in beech forests on limestone in southern Lower Sa xonia (Germany). To investigate the effect of high protozoan numbers o n earthworm distribution, a multiple choice feeding experiment was set up in fumigated soil, reinoculated with different numbers of naked am oebae, protozoa commonly found in that soil. Distribution of Aporrecto dea caliginosa (Savigny) after wk was correlated with numbers of amoeb ae in soil. Other experiments confirmed digestion of protozoa by earth worms. The weight gain of young A. caliginosa in soil with amoebae was twice that in soil without protozoa. Direct observations of fresh cas t material confirmed that active protozoa were digested by A. caligino sa. Lower protozoan numbers in faeces of Octolasion lacteum (Orley) th an in the surrounding soil were found by dilution series, indicating g razing on the active part of soil protozoa by earthworms. The experime nts provide evidence that A. caliginosa is actively searching for plac es with high protozoan densities and that protozoa may play a signific ant role in earthworm nutrition. (C) 1997 Elsevier Science Ltd.