Effects of hydrological intermittency and anthropogenic pressure on aquatic beetle assemblages in the Martil River...

This study investigates the spatiotemporal dynamics of aquatic beetle assemblages in the Martil River, northern Morocco, where hydrological intermittency and anthropogenic pressures threaten aquatic diversity and endemism. Over four seasons (spring, summer, autumn 2017, and winter 2018), we sampled 16 sites, grouped into four categories (A-D) along altitudinal and land-use gradients. Our surveys recorded 1,268 individuals representing 50 species from 10 families. Richness and abundance peaked in natural and/or permanent reaches (groups A-B), declining sharply downstream under urbanization and pollution (groups C-D). Gyrinidae dominated numerically (54%), while Dytiscidae exhibited the highest diversity.Adephaga prevailed during dry periods with lentic affinities, in contrast to Polyphaga, which were associated with wet-season lotic conditions. Predators (73%) and swimmers (72%) represented the main functional feeding and locomotion groups. Correspondence analysis revealed seasonal segregation, with rheophilic taxa in wet flows, thermophiles in summer pools, and eurytherms in spring. Co-inertia analysis (CIA) ordination highlighted upstream and midstream refuges with high dissolved oxygen that support sensitive species, in contrast to lowland, slow-flowing streams with elevated BOD₅, COD, and conductivity, where more tolerant generalist species dominate. Beta-diversity partitioning showed that species turnover (βsim) was the main component of community dissimilarity. PERMANOVA confirmed significant compositional differences between urban and non-urban assemblages. These findings highlight the importance of incorporating permanent mid-reaches into conservation planning and demonstrate the potential of aquatic beetles as indicators of hydrological intermittency.