Moss- and mineral substrata-dwelling meiobenthos in two different low-order streams

Abstract

The quantitative composition of permanent and temporary meiobenthos inhabiting an aquatic moss Fontinalis antipyretica and the surrounding mineral substrate in two different low-order streams was investigated, as were the amounts of fine organic and mineral matter trapped within both mesohabitats. Densities of moss-dwelling meiofauna were one order of magnitude higher than densities in the surrounding mineral bed. Total meiofauna in the third-order stream Bystřice (Czech Republic) were nearly 3-times more abundant than in the second-order stream Oberer Seebach (Austria), most likely reflecting the higher amount of fine organic matter in the Bystřice. Dominant meiobenthic groups in both streams and substrata were Rotifera, Chironomidae and Nematoda. However, Harpacticoida was the second most abundant group in gravel of the Oberer Seebach. Temporary meiofauna, mostly early-instar chironomid larvae, represented 40-60% of total meiofaunal densities. Most correlations between meiofaunal densities and trapped fine particles likely reflect passive deposition of meiofauna within investigated substrata. However, positive correlations between Monogononta, Nematoda, Oligochaeta, Harpacticoida and Chironomidae densities in moss and organic particles in the size range of 30-100 μm may indicate a feeding relationship. Fine organic matter biomass was significantly lower in moss compared to gravel in the Oberer Seebach; no significant difference was found in the Bystřice. We found an indication that the capacity of moss and surrounding mineral substrata in trapping fine organic particles in relation to flow velocity differed during the sampling period. Moreover, it is questionable whether F. antipyretica can serve as a refuge from current for stream meiobenthos.