Environmental Gradients Shaping the Freshwater Bryophyte Communities of Croatia (Western Balkans)

Abstract

A comprehensive field survey of 527 sites on 293 watercourses across Croatia revealed 76 sites (14.42%) in which bryophytes were the dominant part of the macrophyte vegetation. Using classification and ordination analyses, we obtained five community types segregated across the gradients of several climatic, physiographic and water chemistry parameters. The Didymodon tophaceus–Apopellia endiviifolia and the Berula erecta-Cratoneuron filicinum communities were mostly confined to the clean and basic karstic rivers of the Dinaric Ecoregion under the influence of the Mediterranean climate, with the Didymodon tophaceus–Apopellia endiviifolia community being a tufa-forming community associated with the seasonally dry watercourses of small catchment areas and cascades along the larger karstic rivers, while the Berula erecta–Cratoneuton filicinum community was mostly associated with rivers with larger catchment areas and permanent flow. On the other hand, the Oxyrrhynchium hians–Chiloscyphus pallescens community and the Fissidens pusillus–Veronica beccabunga community were associated with eutrophic water restricted to small rivers of the Pannonian Ecoregion under the influence of the temperate climate and flowing over silicate bedrock. The most represented and widespread in Croatia was the Cinclidotus community, displaying the widest ecological range in the study. It was mostly associated with the relatively clean karstic rivers of large catchment areas belonging to the Dinaric Ecoregion, with the majority of the sites under the influence of a temperate climate with higher precipitation during the warm period of the year. The geographical patterns of the freshwater bryophyte communities showed that the relatively clean, fast and cold karstic rivers belonging to the Dinaric Ecoregion provide habitats that harbour a greater diversity of bryophyte communities than the watercourses of the Pannonian Ecoregion, where bryophyte-dominated communities are restricted to a small number of small lowland and semi-montane rivers and predominantly occupy periodically flooded microhabitats such as river margins.

Ecological Preferences and Indication Potential of Freshwater Bryophytes–Insights from Croatian Watercourses

“…These rivers flow over carbonate bedrock which influences water pH and alkalinity, as well as species assemblages where basophilous, i.e., acid-sensitive, taxa dominate. An important influence of geology, water pH and alkalinity on aquatic bryophytes has been already demonstrated on the European level [1,2,4,5,30,39,57] and beyond [6,17,40,59], and clear segregation of aquatic bryophytes along the alkalinity and pH gradient was recently demonstrated for Croatian bryophytedominated watercourses as well [22]. The latter study identified three communities characterized by different basophilous species which were mostly associated with karstic rivers of the Dinaric Ecoregion, and two communities in small rivers situated in the Pannonian Ecoregion, which were dominated by a high share of hygrophyte taxa inhabiting periodically flooded river margins.…”

“…The majority of the species included in our study preferred near-neutral to basic water, with the mosses Eucladium verticillatum, Didymodon tophaceues, Palustriella falcata, Brachythecium rivulare, Fissidens crassipes and Cinclidotus aquaticus, as well as the liverworts Apopellia endiviifolia and Chiloscyphus polyanthos, being most strongly associated with higher water pH and having high frequencies and abundance in the watercourses of the Dinaric Ecoregion. This ecoregion is known to harbor greater diversity regarding freshwater bryophytes [15] and their communities [22] since its fast, cold montane and semi-montane karstic rivers with larger and more stable substrates provide more suitable habitats than the lowland rivers of the Pannonian Ecoregion, which are usually slow and warmer, with dominantly sandy and gravelly substrates. This was demonstrated in our study as well, with the highest number of species recorded in montane and mid-altitude small watercourses, followed by montane and mid-altitude medium and large watercourses of the Continental Subecoregion, which are both characterized by the dominance of large and medium substrates.…”

“…Here, the aquatic form of Riccia fluitans was recorded floating mostly in stagnant waters of hypereutrophic artificial canals, while Leptodyctium riparium was growing on rarely present large stable rocks, dead wood, periodically submerged tree bases and margins of the watercourses, having the highest frequency in lowland small watercourses, followed by lowland medium and large watercourses. These watercourses naturally have higher trophic status and the vast majority of them are additionally subjected to substantial changes in land use associated with high nutrient input, as well as hydromorphological degradation [66], which are known to reduce habitat quality for bryophytes, resulting in reduced cover, diversity and changes in community structure [14,17,20,22]. Thus, as expected, freshwater bryophytes which occur in higher frequency within this region are those which can tolerate poorer water-quality and inhabit less-natural catchment areas, such as Leptodictyum riparium, Cratoneuron filicinum, Cinclidotus riparius, Rhynchostegium riparioides, Fontinalis antipyretica and Fissidens crassipes.…”

“…While the presence and coverage of freshwater bryophytes are primarily determined by riverbed stability and substrate size [16][17][18], physiographic, geological, climatic and Plants 2022, 11, 3451 2 of 29 water chemistry factors have been identified as major environmental drivers influencing species diversity and composition [1][2][3][16][17][18][19][20][21][22]. Furthermore, changes in stream and river hydrology and morphology, as well as anthropogenically influenced changes in water chemistry, strongly impact individual bryophyte species and whole communities [20,23,24].…”

Selection of Dominant Moss Species for Ecological Restoration of Abandoned Mines – A Case Study of Tieshan Quarry in Qixing District, Guilin, China

“…In this study, mosses are distributed vertically, and the plant coverage and species diversity at the bottom of the slope are high (table 1). Under the dominance of the subtropical monsoon climate, the region has abundant rainfall, and the high and steep slopes are washed by unidirectional runoff, which reshapes the distribution of mosses [29]. High and steep rocky slopes are difficult to retain water, so air humidity, as an important source of water for mosses, plays an important role in the development of mosses.…”