Relevance of intermittent rivers and ephemeral mountain streams on the diversity of amphibious lichens

Abstract

Intermittent rivers and ephemeral streams are watercourses that cease flowing and/or completely dry out at some point in time and space. This temporal dynamic requires organisms to adapt to the varying immersion and drying cycles in terms of time and intensity. Among the organisms adapted to these environments are amphibious or semiaquatic lichens who colonize stable rocks in non-eutrophicated waters. Given the morphological and anatomical adaptations that lichens have developed to survive in such environments, we assess their specificity to aquatic environments and their potential to thrive in terrestrial habitats. Here, we selected fifty lichen species with a preference for freshwater habitats and retrieved information from the records available in the GBIF Spain database. Supplementary habitat information was obtained from relevant bibliographic references when needed. The results showed a strong specificity for aquatic environments among the 36 species that commonly thrive in submerged or inundated areas after rainfall. We highlight the presence of a few rare species such as Pseudosagedia guentheri, Polyblastia quartzina and Pyrenocollema saxicola, which have only been reported once or twice. Notably, a significant proportion of these records were associated to aquatic systems in mountainous areas (>1300 m in altitude). Overall, watercourses in mountainous regions constitute suitable habitats for the development of amphibious lichens, especially in gorges and rapids, characterized by oligotrophic waters and extensive exposed rock surfaces.