Mass occurrence of algal-feeding tardigrade Apodibius confusus, in the young soils of a post-mining site

At the coal-mining site 'Chicken Creek' (Spremberg, Germany), primary succession of the soil tardigrade community was investigated over a period of 4 years after initial soil deposition in 2005. During the first 2 years of succession, tardigrades occurred only sporadically and in very small numbers. In October 2007, algal-feeding Apodibius confusus first appeared at the site with small-scale mass densities of up to 2281 individuals in only 10 cm2 of top soil. A. confusus from then on dominated the soils (98% of overall tardigrade counts). From October 2007 to May 2009, its distribution changed from patchy to homogenously and its mean densities gradually increased to 328.7 thousand tardigrades m-2. In May 2009, A. confusus was present in 100% of the samples, while at the same time, new tardigrade species became established, the second frequent species being Hexapodibius cf. micronyx (3% of overall counts). With A. confusus and H. cf. micronyx, two tardigrades with reduced claws inhabit the 'Chicken Creek' sites: complete lack of claws in the genus Apodibius and 4th pair of claws missing in the genus Hexapodibius. The use of claws in the pore system of coarse soil substrates and the necessity to clarify the position of Apodibius and Hexapodibius in the system of Tardigrada is discussed. At the moment, we intend to culture A. confusus to observe its locomotion and to provide life history data and alternative food sources of the species.