THE ENCHYTRAEID COGNETTIA-SPHAGNETORUM IN RISK ASSESSMENT - ADVANTAGES AND DISADVANTAGES

The enchytraeid Cognettia sphagnetorum reproduces asexually by fragmen tation. Mortality and growth of P- and F-generations, size at fragment ation, number of fragments produced, and fragmentation rates were eval uated in two series of copper-treated soils. Specimens were individual ly maintained and fed either the fungus Mortierella isabellina or gree n algae (Pleurococcus spp.). Mortality was low when C. sphagnetorum wa s fed M. isabellina. Growth rate and size of the individual at fragmen tation decreased significantly with increasing metal concentration. Wo rms in control soil split into five fragments, whereas those maintaine d at high copper concentrations produced only two. When the worms were fed Pleurococcus the growth rate was doubled. At low copper concentra tions 11-12 fragments were produced at fragmentation. Retarded growth and reduced fragmentation rates occurred at higher copper concentratio ns than when fed M. isabellina. Overall, C. sphagnetorum sustained cop per better in the Pleurococcus situation. The differences in the outco me of the series show the importance of food quality in long-term test s and the need to standardize food items; optimum respective sub-optim um conditions can be created when food is to be added. The advantages and disadvantages of using C. sphagnetorum in risk assessment are disc ussed.