Concordance of stream macroinvertebrate assemblage classifications: How general are patterns from single-year surveys?

We examined how the assemblage structure and assemblage–environment relationships of stream macroinvertebrates varied over three consecutive years in a boreal drainage system. We specifically examined whether classifications produced assemblage types that were stable through time, and how these assemblages could be predicted based on local environmental variables. We also used a combination of Procrustes rotation analysis and NMDS ordinations to examine the degree of year-to-year concordance of assemblage patterns. The composition of site clusters varied among years, resulting in only moderate among-year concordance of assemblage classifications. Stream width and in-stream habitat conditions, especially macrophyte cover, were the most important variables discriminating among the cluster groups. Despite temporally variable assemblage classifications, the overall macroinvertebrate assemblage structure was concordant among years. Among-year concordance was higher in-streams with low temporal variation in the physical environment, as well as high abundance and low variability of macrophytes. Due to among-year variability in cluster composition and weakly predictable assemblage–environment relationships, a posteriori assemblage classifications may be of limited value in the conservation planning of headwater streams.