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Aquatic bryophytes of Croatia – distribution, ecology and threats

An extensive macrophyte field survey of running and standing waters was conducted from 2016 to 2021 at 786 sampling sites across Croatia. This survey is the first to present a comprehensive floristic catalogue of the freshwater bryoflora, along with an analysis of the distribution and diversity patterns on a national level. In all, 83 bryophyte species (68 mosses and 15 liverworts) were recorded in 228 sites, with average species richness of 4.17 species per site. The most frequent species were Fontinalis antipyretica, Rhynchostegium riparioides, Leptodictyum riparium and Cratoneuron filicinum. The majority of the species encountered were rarely found with over 70% of species recorded on less than 10 sampling sites and the majority of the species not being truly aquatic, rather being classified as facultative aquatics. Bryophytes were the dominant component of the macrophyte vegetation in 76 sites. Classification and ordination analyses of these sites revealed five community types segregated across the gradients of several climatic, physiographic and water chemistry parameters. The Didymodon tophaceus–Apopellia endiviifolia and the Berula erecta-Cratoneuton filicinum communities were associated with basic and alkaline, clean water with low nutrient content. They were mostly recorded to karstic rivers of the Dinaric Ecoregion under the influence of the Mediterranean climate. Didymodon tophaceus–Apopellia endiviifolia community was a tufa-forming community associated with seasonally dry watercourses of a small catchment area and cascades along the karstic rivers, while Berula erecta-Cratoneuton filicinum community was associated with Mediterranean rivers with a larger catchment area and permanent flow. On the other hand, the Oxyrrhynchium hians-Chiloscyphus pallescens and Fissidens pusillus-Veronica beccabunga communities were mainly restricted to small rivers of the Pannonian Ecoregion under the influence of the temperate climate, associated with water of low alkalinity and higher nutrient content. Finally, the Cinclidotus community was the most represented and widespread in Croatia with a wide ecological range, however, with the majority of the sites situated on karstic rivers of the Dinaric Ecoregion. Both, floristic and vegetation analysis have revealed that this region provides more aquatic habitats and microhabitats suitable for the freshwater bryophytes, while in the Pannonian Ecoregion freshwater bryophytes are restricted the periodically submerged riparian zones and are more threatened by unsuitable water management.

bryophytes ; Croatia ; freshwater ; karstic rivers

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