The effects of predation by juvenile fish on the meiobenthic community structure in a natural pond

1. Benthic communities in aquatic ecosystems include an abundant and functionally important meiofaunal component. The effects of predation by fish on zooplankton, macroinvertebrates and periphyton in freshwater habitats have been clearly demonstrated, whereas impacts on meiofaunal assemblages are poorly understood. 2. In this study, the predation effects of benthivorous juvenile carp (Cyprinus carpio) on the abundance, biomass, secondary production, size classes and community structure of meiofaunal assemblages and on nematode diversity in the littoral zone of a natural freshwater pond were examined over 125days using field enclosures and exclosures. 3. Fish predation altered the abundance, biomass and secondary production of nematodes, oligochaetes and microcrustaceans (cyclopoids, harpacticoids, ostracods and cladocerans) but not of rotifers. These changes were consistent with top-down control of the freshwater meiofaunal assemblages in the natural pond over time. By contrast, small-bodied meiofauna were more abundant in the presence of fish, suggesting indirect facilitation. Both species richness and species composition but not the diversity of the nematode community were affected by fish predation. 4. Removal of the fish from the enclosures resulted in the thorough recovery of the density, biomass and secondary production of nematodes, oligochaetes and microcrustaceans within 45days. 5. The results indicate that predation by juvenile freshwater fish depresses the overall abundance, biomass and secondary production of meiofaunal assemblages, except in the case of rotifers, and alters the size structure of the meiofaunal community. Our study provides insight into the food-web ecology of lakes and the first evidence of freshwater fish predation effects on meiofaunal assemblages in a natural habitat.