ABSTRACT The epikarst, forming the uppermost layer of the vadose zone, is the interface between surface water and groundwater in karst aquifers, influencing hydrology and providing habitats for subterranean invertebrates. Epikarst invertebrates, including copepods, play important ecological roles. However, copepod taxonomic and molecular diversity in epikarst waters remains poorly understood. We examined diversity patterns and their relationship to environmental variation in epikarst seepage within the Demänová Karst, Slovakia. Copepods were sampled monthly from May 2019 to July 2020, using 27 epikarst water filtering devices installed across four caves. Specimens were morphologically identified, largely to species level, and genetically characterised using mitochondrial COI barcode sequences. We quantified haplotype and nucleotide diversity, evaluated population structure, inferred demographic patterns and analysed relationships between environmental variables, copepod occurrence and assemblage composition. Analysis of 536 copepod individuals revealed distinct mitochondrial lineages within Elaphoidella and Bryocamptus species. Elaphoidella droppai showed signals consistent with recent expansion, whereas Elaphoidella phreatica exhibited more complex demographic patterns. Environmental variables, particularly drip rate, pH and ceiling thickness were associated with variation in copepod occurrence and assemblage composition. These results indicate that variation in both hydrological and structural characteristics of the epikarst influences copepod assemblages. The occurrence of multiple mitochondrial lineages within several species further suggests that species diversity in epikarst copepods may be underestimated when based solely on morphology. By integrating ecological measurements with genetic data, this study refines understanding of how environmental gradients and demographic processes shape copepod assemblages in epikarst habitats. Our findings highlight the importance of environmental conditions for the occurrence and composition of groundwater communities and demonstrate that morphology‐based assessments alone may underestimate copepod diversity.
Rendoš et al. (Wed,) studied this question.