Influence of fine sediments on meiofauna colonization densities in artificial stream channels

Abstract

Excessive fine sediments have been shown to adversely affect abundance and diversity of stream macroinvertebrates, but effects on meiofauna have been only minimally and indirectly assessed. We used 12 artificial channels in a 4 th order Ozark stream to investigate the influence of silt (particle diameter 63 μm to 2 mm) and gravel (particle diameter 2 to 16 mm) on meiofauna colonization. Four channels were filled with gravel, four with 1/2 gravel and 1/2 sand, and four with 1/3 gravel, 1/3 sand, and 1/3 topsoil, referred to as gravel, sand, and silt treatments, respectively. Substrate cores were taken from the natural and artificial channels for analysis of meiofauna (80 μm to 1 mm) and substrate composition. Rotifera, Copepoda, Chironomidae, Nematoda, Oligochaeta, and Mollusca (principally juvenile Corbicula fluminea) comprised the major meiofauna taxa. Total meiofauna density in the artificial channels differed significantly among treatments. Density was lower in the silt treatment than in gravel or sand treatments, but overall densities in the gravel and sand treatments did not differ. Responses to treatments varied among specific taxa; densities of rotifers, copepods, nematodes, and oligochaetes were lower in the silt than the gravel treatment, but chironomids and nematodes were equally abundant in gravel and sand treatments, while lower in the silt treatment. Total meiofauna density did not differ between the natural channel and the gravel treatment but was lower in the sand and silt treatments. Copepod density was higher in the gravel treatment, and nematode, oligochaete, and mollusk densities were lower for all three treatments compared to the natural channel. The lower density of total meiofauna associated with high concentrations of silt suggests that excessive silt reduces habitat space and/or quality for meiobenthic organisms, while a sand and gravel mix is suitable for some meiofauna taxa.