Benthic mesocosm experiments have shown that subtidal macrofauna species with contrasting feedlng behaviour and mobility can alter the structure of natural subtidal meiobenthic nematode assemblages. Test macrofauna species were the bivalves Nuculoma tenuis (subsurface-deposit feeder) and Abra alba (surface-deposiWsuspension feeder) at 3 different densities and the heart urchin Brissopsis lyrifera (subsurface burrowing deposit feeder) at a single density. a and P nematode diversity were affected by disturbance of different intensities in the bivalve treatments in a way that is consistent with the intermediate disturbance hypothesis regardless of type of disturbance. These measures of community structure did not differentiate between contrasting types of disturbance. Multivariate community analysis indicated that the species response in the assemblage was more sensitive to the type of disturbance than the intensity of disturbance. Differential responses of the nematode species did not reflect their depth distribution in natural field sediment and the likely depth at which the test macrofauna species were active. Nor was the response simply a predator-prey interaction with certain species targeted by the predator; the interactions appear to be more complex. Our experimental results suggest that patches of sediment which are dominated by hlgh abundances or biomass of one or a few species, a situat~on which is encountered in the field, are important in maintaining regional diversity. These patches will create a heterogeneous mosaic of communities with different diversities and different species compositions