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Due to the lack of empirical data, meiofauna are often underestimated as prey for freshwater animals and are commonly regarded as trophic dead ends. Here we present a synthesis of recent evidence showing that meiofauna are significant as prey, not only for many benthic macroinvertebrates (chironomids, shrimps, and flatworms) but also for juveniles of widespread freshwater bottom-feeding fish species (e.g., carps, gudgeons, catfish). In this review, we focus on the following questions: (1) Which groups consume meiofauna? (2) In what amounts are meiofauna ingested? (3) Does predatory feeding behavior influence natural meiofaunal communities? (4) Are meiofauna organisms actively ingested or are they bycatch? To answer these questions, we focused on studies that included gut/feces analyses of potential predators and empirical investigations conducted in the laboratory (e.g., functional response experiments and microcosm studies) and in the field (enclosure/ exclosure settings). We were able to demonstrate that meiofauna taxa are consumed in high numbers by a wide range of larger organisms. This predation can significantly shape meiofaunal communities, by reducing the abundance, biomass, and production of certain members of the investigated assemblages. However, in most cases, it remains unclear if there is an active predation of meiofauna or a passive ingestion by unselective feeding.

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Meiofaunal abundance, biomass and secondary production were investigated over 13 months in an unpolluted first-order stream. Four microhabitats were considered: sediment and the biofilms on dead wood, macrophytes and leaf litter. The relative contribution of the microhabitats to secondary production and the influence of environmental factors on meiofaunal density distribution were estimated. We expected (1) meiofaunal abundance and biomass to exhibit seasonal patterns, with more pronounced seasonal fluctuations on macrophytes and leaf litter than in the other microhabitats, (2) annual secondary production to be highest in sediment; however, the relative contribution of the microhabitats to monthly secondary production would change during the year, and (3) a bottom-up driven influence on meiofaunal density distribution in the microhabitats. Meiofaunal annual mean abundance, biomass and secondary production were 7–14 times higher in sediment and on dead wood than on macrophytes and leaf litter. Significant seasonal patterns described the meiofaunal abundance in sediment and on leaf litter as well as the biomass in sediment, on macrophytes and leaf litter. Organisms in sediment and on dead wood contributed 48 and 43%, respectively, to secondary production m−2, but in regard to the stream area covered by the microhabitats, sediment had the highest share (80%). Significant determinants of the density distribution were AFDM, protozoans, bacteria and Chl-a, which influenced all meiofaunal groups. Our study clearly indicates that meiofaunal organisms in sediment and on dead wood have a remarkable share on total secondary production of lotic systems which is especially relevant for forested low-order streams.

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