Meiobenthic response to river-borne benthic particulate matter -: a microcosm experiment

1. Benthic communities inhabiting river-lake interfaces are confronted with temporal variation in the import of river-borne material to the associated littoral zone. The primary objective of this study was to evaluate the exposure to river-borne benthic particulate matter as a force shaping the meiofauna of the river-lake interface. 2. In a 2 x 2 factorial design, combinations of strongly and weakly river-influenced communities (near or far from the river mouth) with and without river-borne benthic particulate matter enrichment were studied in laboratory microcosms to assess the response of the heterotrophic meiobenthos to river-borne matter. 3. Nematodes dominated both habitat types and were the only meiofaunal taxon that responded to the enrichment. 4. A strong interactive effect between experimental enrichment and location of site was observed. Whereas nematodes from the littoral habitat close to the river mouth responded to the enrichment only marginally, nematodes from the remote site were strongly affected in the presence of river-borne particulate matter. 5. In the non-enriched samples of the remote site, the number of nematodes increased greatly over time. Among nematode feeding types, deposit feeders dominated over chewers at the beginning of the experiment but both types were equally abundant at the end. In the presence of river-borne matter the increase of chewers ceased and a shift in feeding type composition did not occur. 6. It was shown that for river-lake interface meiofaunal assemblages in relative proximity, the same taxon might respond differently if exposed to an external pressure, e.g. river-borne components. These components may have a stronger influence on taxa with longer life cycles.