Karst landscapes are a set of various features built of rocks that are soluble in water

This study presents the first comprehensive investigation of population aspects and ecological traits of water beetles in oligotrophic hydrosystems with tufa formation in southeastern Europe. Diverse lotic habitats (springs, rivers and tufa barriers) were investigated monthly for one year in Plitvice Lakes National Park in Croatia. Elmidae were the most diverse and abundant family, followed by Scirtidae and Hydraenidae. The ecological traits of water beetles were primarily defined by nutrients and water depth. Elmis bosnica Zaitzev, 1908, about which little has been published, was found to be bryophilous and to prefer low water temperatures. Biogeographical analysis revealed the dominance of typical southeastern and Mediterranean species. Species population dynamics could be attributed to differences in flow permanence, current velocity and canopy coverage. Both current velocity and water depth significantly influenced the occurrence of larval stages, while abundance of adults correlated with water depth. Our results highlight tufa barriers as preferred habitats for species of the genus Riolus and the family Scirtidae. The results of this study, many of which are the first to be reported for water beetles, provide a basis for further investigations of these animals and their ecology in oligotrophic hydrosystems with tufa. In particular, our study demonstrates the potential of Elmidae as water quality indicators, which should be considered in future conservation and protection management efforts. This study presents the first comprehensive investigation of water beetles in oligotrophic hydrosystems with tufa formation in southeastern Europe. Biological and ecological traits of so far poorly studied species are revealed.The results provide a basis for future investigations, and demonstrate the potential of Elmidae as water quality indicators in this region.

Although freshwater habitats, especially springs, are widely recognized as top-priority habitats for monitoring and conservation procedures, their fauna, especially water beetles, are still poorly studied in the southeastern part of Europe. Thus, the dominant water beetle in these habitats, E. bosnica (Zaitzev, 1908) (Insecta: Coleoptera: Elmidae), has been completely ignored and misidentified. This study represents the first review of its taxonomy and its population and ecological traits. Both published and unpublished data are presented and discussed, as well as the results of field sampling in 46 springs and other waterbodies conducted in this region from 2004 to 2019. The identification characters of the male genitalia and the first DNA barcode of the species are presented. The results confirm the close phylogenetic relationship of E. bosnica with E. aenea (Müller, 1806) and E. rioloides (Kuwert, 1890). The species proved to be a useful environmental descriptor and can easily be used as a biological indicator due to its easy identification. The species shows remarkable sensitivity to environmental conditions and inhabits sites that are potentially under increased anthropogenic pressure and could disappear at an alarming rate. Thus, karstic habitats should be included in future conservation and monitoring procedures in this part of Europe.

Due to ongoing changes and a decline in biodiversity, science today should rely on long-term species-based ecological studies. We have conducted a long-term ecological dynamics study on the water beetle family Scirtidae, which, although it is very abundant in benthic communities, is still poorly studied. The main objective of this study was to investigate the population aspects (composition, diversity, sex ratio) and ecological aspects (emergence patterns, seasonal dynamics and preferences for environmental factors) of the family Scirtidae over 15 years in Plitvice Lakes NP, Croatia. The study was conducted at three sites and in five different substrate types. A total of three taxa with different distributions were recorded in the study area: Hydrocyphon novaki and H. deflexicollis on the tufa barriers and the Elodes sp. in the spring area. The sex ratio was in favour of males in spring and early summer, while it shifted in favour of females towards the end of autumn. The abundance and emergence of the family were primarily determined by the environmental parameters which showed the greatest fluctuations over a period of 15 years: water temperature, water discharge and oxygen saturation. Our results clearly show that Scirtidae can be used as indicators of stream zonation and habitat quality. Based on the methodology and the results of this study, we conclude that Scirtidae should be used in future monitoring and protection measures in karst freshwater habitats in southeastern Europe.

Functional diversity is a key component of biodiversity that reflects various dimensions of ecosystem functioning and the roles organisms play within communities and ecosystems. It is widely used to understand how ecological processes influence biotic assemblages. With an aim to increase our knowledge about dragonfly ecological requirements in tufa-depositing karst habitats, we assessed functional diversity of their assemblages, various life history traits (e.g., stream zonation preference, substrate preference, reproduction type), and relationship between functional diversity and physico-chemical water properties in three types of karst lotic habitats (springs, streams, and tufa barriers) in a biodiversity hotspot in the western Balkan Peninsula. Dragonfly functional diversity was mainly characterized by traits typical for lotic rheophile species with medium dispersal capacity. Among the investigated habitats, tufa barriers, characterized by higher (micro)habitat heterogeneity, higher water velocity, as well as lower conductivity and concentration of nitrates, can be considered as dragonfly functional diversity hotspots. Functional diversity and most of the life history traits were comparable among different substrate types in the studied habitats, indicating higher importance of habitat type in shaping dragonfly functional diversity patterns in karst lotic habitats. Our results should be considered in the management and conservation activities of vulnerable karst freshwater ecosystems and their dragonfly assemblages.