Online first articles

Understanding the dynamics of aquatic ecosystems is essential for biodiversity conservation, as ecological processes and species interactions respond sensitively to environmental variation. It is well established that various environmental factors influence species distribution in aquatic systems, both in surface (epigean) and subterranean (hypogean) environments. However, the absence of light in subterranean habitats can create distinct environmental conditions that may alter the composition and structure of biological communities compared to those in surface habitats. In this study, we analyzed the physicochemical parameters of the water and the structural organization of aquatic benthic invertebrate communities along a 300-meter stream that flows through both epigean and hypogean sections. Environmental variables differed markedly between the two sections, and these differences were reflected in the measured parameters along the sampling gradient. A tributary draining epikarst infiltration influenced the environmental conditions within the main cave passage. The species composition of the aquatic invertebrate community also varied between surface and subterranean sections. However, certain species were dominant in both and were key components of the lotic system. Most species were sensitive to the extreme conditions in the cave, including total darkness and limited food availability. The main cave passage was identified as an ecotonal transition zone, where the interface between hypogean and epigean environments acts as a selective filter along the stream continuum, directly shaping the structure of the aquatic community. The findings of this study offer valuable insights for conservation strategies aimed at preserving biodiversity in hypogean ecosystems with similar environmental characteristics.