Seasonal Variation Outweighs Spatial Variation in Lotic Water Mite Communities in a Mediterranean Mountain

Water mites (Hydrachnidia) are diverse, ecologically important arachnids that can serve as effective bioindicators; however, their communities in Mediterranean mountain rivers are scarcely documented. The present study provides a comprehensive analysis of water mite communities in mountain rivers of Serra da Estrela (Portugal), assessing how abundance, genus richness, and community composition vary across seasons, among rivers, and along an elevational gradient. Water mites were sampled in twelve sites belonging to 3 rivers across an elevational gradient and in three seasons. In total, 7296 adult water mites were collected, representing 33 genera and 17 families. Three genera were documented for the first time in Portugal: Albia, Hexaxonopsalbia, and Wettina. Abundance varied with season, being lower in spring (102 ± 35 specimens per site) than in summer (249 ± 73) and autumn (257 ± 83). Genus richness showed a similar pattern, with lower values in spring (9.8 ± 2.0) than in summer (12.2 ± 1.9). Spatial variation among rivers was comparatively minor. The multivariate analysis revealed that community-level changes between seasons, rivers and elevation were driven by only a few genera. The findings help improve the knowledge of Mediterranean mountain water mite communities, shedding light on their seasonal and spatial dynamics.