DISPERSAL AND FRAGMENTATION OF THE ENCHYTRAEID COGNETTIA-SPHAGNETORUMIN METAL POLLUTED SOIL

A number of patches of high quality will most probably be present even in soil of a generally low quality, e.g. caused by a patchy distribut ion of industrially emitted metal pollution, making it possible for so il invertebrate populations to sustain at low densities. The abilities to disperse, recognize a favourable patch, orientate towards it and s uccessfully colonize it will then increase the survival potential of a n individual and its progeny. To understand how enchytraeids can survi ve in metal polluted soil a number of laboratory experiments were carr ied out. They focussed on dispersal ability, reproduction and the abil ity to avoid polluted soil of the enchytraeid worm Cognettia sphagneto rum (Vejdovsky). The worm reproduces by dividing into two to several f ragments which regenerate head, tail or both. Adults (> 35 segments) o f C. sphagnetorum um sampled in mor soil of a coniferous forest were u sed to test the impact of metal polluted (mainly Cu + Zn) soil on the variables mentioned above. C. sphagnetorum had a rather low dispersal rate which was unaffected by soil metal concentrations; 5% of the popu lation covered 6 cm within two weeks while 75% did not move at all. Th e species avoided high metal concentrations and, when forced to inhabi t metal polluted soil, the mortality rate increased in soils with more than 1670 mg Cu + Zn kg(-1) dry mass. The highest rate of fragmentati on was found in soil with a metal content of 3300 mg Cu + Zn kg(-1) so il dry mass and more fragments than unchanged adults were found in soi ls containing more than 850 mg Cu + Zn kg(-1) soil dry mass, suggestin g an induced fragmentation. There seemed to be an upper limit to the a ccumulation of copper (20 mu g Cu mg(-1) dry mass body tissue), while zinc was accumulated in direct proportion to the concentration of the substrate. C. sphagnetorum is a potential candidate for use in soil to xicity tests focussing on biological variables as it is abundant and i nhabits the uppermost centimeters of the soil layer which often is mos t affected by anthropogenic activities.