Effects of biological disturbance on diversity and structure of meiobenthic nematode communities

Benthic mesocosm experiments have shown that subtidal macrofauna species wi th contrasting feeding behaviour and mobility can alter the structure of na tural subtidal meiobenthic nematode assemblages. Test macrofauna species we re the bivalves Nuculoma tenuis (subsurface-deposit feeder) and Abra alba ( surface-deposit/suspension feeder) at 3 different densities and the heart u rchin Brissopsis lyrifera (subsurface burrowing deposit feeder) at a single density, alpha and beta nematode diversity were affected by disturbance of different intensities in the bivalve treatments in a way that is consisten t with the intermediate disturbance hypothesis regardless of type of distur bance. 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 o f the nematode species did not reflect their depth distribution in natural field sediment and the Likely depth at which the test macrofauna species we re active. Nor was the response simply a predator-prey interaction with cer tain species targeted by the predator; the interactions appear to be more c omplex. Our experimental results suggest that patches of sediment which are dominated by high abundances or biomass of one or a few species, a situati 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.