Abstract
Concrete revetment is widely applied in flood control to protect stream banks from a scouring. However, the utilization of concrete substrates by stream invertebrates is largely unknown to the present. In this study, we conducted a field survey on the physical habitat environment and community structure of stream invertebrates on concrete, stone and bedrock substrates, in order to characterize concrete substrate relative to natural substrates. Current velocity was lower on stone substrate than on concrete or bedrock, probably because of high roughness of stone substrate. Density of stream invertebrates was the highest on concrete substrate, while the evenness, one element of diversity, was lower on concrete and bedrock than on stone. In addition, the ordination using non-metric multidimensional scaling (NMS) revealed that the community structure of stream invertebrates on concrete was different from that on stone and can be characteristics by high density of Baetiella japonica, with bedrock showing intermediate characteristics between concrete and stone. Thus, stream invertebrate assemblage established on concrete substrate appeared to be distinct from those of natural substrates, possibly owing to low habitat complexity. High density, low taxon richness and low evenness of stream invertebrates were observed at the habitat with high current velocity. The value of NMS axis 2, which positively and strongly correlated with the density of Baetiella japonica, increased as the current velocity increased. Distinctive community structure, characterized by high density and low evenness, observed on concrete substrate would thus be caused by high current velocity and habitat preference of Baetiella japonica. Consequently, we suggest that concrete revetment modifies the community structure of stream invertebrates by simplifying and altering physical habitat environment, at the habitat patch scale examined in this study. Our findings could contribute to better understanding of the influences of flood control structures on stream invertebrates and, furthermore, provide basic information needed to the stream management and restoration.
