Environmental drivers and seasonal distribution of endemic macroinvertebrates in the Upper Loukkos Watershed (Northwestern Morocco)

Freshwater ecosystems of the Mediterranean basin are increasingly exposed to hydroclimatic fluctuations, often interacting with sustained anthropogenic pressures. However, in North African rivers, the ecological patterns of endemic aquatic invertebrates remain poorly documented. In this context, the Upper Loukkos Watershed (northern Morocco), a mountainous system within the Intercontinental Mediterranean Biosphere Reserve, provides a relevant setting to examine how environmental gradients and seasonal dynamics influence these assemblages. Endemic macroinvertebrates were sampled across 18 sites during four sampling campaigns (spring and autumn 2014-2015), capturing contrasting hydro-seasonal conditions from drought-induced low flows to post-flood periods. A total of 667 individuals belonging to 24 endemic species were recorded, including Moroccan, Maghrebian, and Ibero-Maghrebian taxa. Diversity metrics varied across sites and seasons, with a clear peak in spring, coinciding with increased flow permanence and partial recovery of hydrological connectivity. The mayfly Choroterpes atlas was the most abundant taxon, whereas the genus Hydraena showed the highest diversity. Multivariate analyses (NMDS, CCA) revealed that environmental gradients strongly structured species distribution. Sites characterized by elevated organic load and suspended solids were associated with disturbance-tolerant taxa (mainly Coleoptera and Hemiptera), whereas well-oxygenated lotic habitats supported rheophilic Ephemeroptera and Plecoptera. Spatial and seasonal patterns revealed a marked turnover in endemic assemblages based on their temporal stability, dominated by intermittent taxa (41.7%); only Hydraena allomorpha was classified as permanent, being recorded throughout all sampling periods. The Jaccard similarity index revealed consistently low overlap in community composition among sampling campaigns, indicating pronounced temporal turnover in the macroinvertebrate assemblage. The predominance of Ibero-Maghrebian taxa underscores the biogeographical significance of the Betico-Rifan region as a link between Europe and Africa. Overall, these findings identify Rif headwaters as key habitats for range-restricted freshwater taxa and highlight their potential role as climatic refugia under increasing hydroclimatic variability. This underscores the need for sustained, long-term monitoring and for explicitly incorporating intermittent and headwater streams into conservation frameworks, which remain underrepresented despite their ecological importance in North African river networks.