Biogeographia – The Journal of Integrative Biogeography

Macroinvertebrate communities in the Upper Loukkos basin (northern Morocco) exhibited marked spatio-temporal variability across contrasting hydrological phases, reflecting the dynamic nature of Mediterranean intermittent systems. Sampling at 18 sites, comprising both protected and impacted reaches, during post-flood and post-drought periods (2014–2015), revealed a total of 102 species. Assemblage composition changed across seasons and sites, largely driven by hydroseasonal dynamics, habitat connectivity, and environmental gradients. Chorological patterns showed a clear predominance of taxa associated with Mediterranean biogeographical affinities, with endemic species accounting for 25% of the assemblage. Protected headwater sites supported higher diversity and a greater proportion of specialist taxa, particularly under post-drought conditions, highlighting their role in maintaining community structure under hydrological variability. Some groups, notably Coleoptera, persisted under low-flow conditions, demonstrating both resistance and recolonisation capacity. Community structure was primarily shaped by interacting environmental and seasonal filters, with a noticeable decline in sensitive lotic taxa, especially during dry periods. Multivariate analyses showed a diffuse community structure across sites and seasons, reflecting the combined effects of hydroseasonal dynamics and environmental gradients on biotic assemblages. Our results indicate that the Upper Loukkos basin acts as a micro-reserve interface, where geographic position, historical context, and topographic complexity contribute to the maintenance of regionally distinctive biodiversity within the western Mediterranean. This highlights the need to integrate multi-scale environmental drivers into biomonitoring frameworks, particularly in intermittent systems where community dynamics remain closely constrained by hydrological variability and where disturbance-sensitive taxa appear especially vulnerable.