Effects of simulated deposition of dredged material on structure of nematode assemblages - the role of burial

A microcosm experiment was designed to evaluate the effects of the simulate d deposition of uncontaminated dredged material on nematode assemblages fro m estuarine intertidal mud. The main objective was to assess the ability of nematodes to migrate vertically into native muddy and non-native sandy sed iment deposited in different amounts and frequencies. Results from univaria te and graphical methods of data-evaluation revealed that nematodes were ca pable of migrating over a wide depth range from the bottom mud layer into t he top layer of deposited sand and mud. A diverse mud assemblage of nematod es was able to survive in nonnative fine sand for the experimental period o f 2 mo. Multivariate analyses showed that the amount of deposit and the fre quency of deposition were interactive factors. A high amount of sediment de posited once at the beginning of the experiment caused more severe changes in assemblage structure than the same amount deposited in more frequent but smaller doses. The response of most species to the experimental treatments appeared to be an integrated response to the enhancing effect of food inpu t accompanying the deposit and the negative effect of burial. Upward migrat ion of nematodes is a process which has often been underestimated in its im portance for recolonisation of areas where uncontaminated dredged material is deposited. Active migration of nematodes can significantly affect the re covery of a dredgings disposal site.