Limnetica 37

Macroinvertebrate communities exhibit wide variability in diversity, abundance and structure on different spatial scales. Space is currently used as an explicit predictor to discriminate between environmental forcing and biotic processes on large- and medium-sized scales, but is generally neglected on smaller scales. To bridge this gap, we considered environmental (depth) and spatial variables (spatial location and structure) to explain the diversity, abundance and community patterns of macroinvertebrate communities on the reach scale by geostatistical and multivariate spatial analyses. Sampling was performed in spring 2015 using a grid sampling design along an intermittent watercourse reach (the Baganza stream, Northern Italy). Overall 5,493 organisms belonging to 25 taxa were collected and identified, with Chironomidae, Baetidae and Naididae being the most abundant taxa. The spatial variables explained a consistent fraction of abundance and taxa richness variability both individually and jointly with depth. The latter was a good predictor of abundance, but not of taxa richness. Our results suggest that while organisms seem able to occupy almost any position in the watercourse, their abundance is modulated by habitat preference. This study represents a starting point to understand how habitat filtering and biotic processes act on macroinvertebrates communities on a very small scale. Our findings improve knowledge about the small scale organisation of macroinvertebrate communities in intermittent streams. Biomonitoring, restoration ecology and habitat suitability modelling could benefit from our approach