Diatom community biodiversity in an Alpine protected area: a study in the Maritime Alps Natural Park

As part of the "All Taxa Biodiversity Inventories" (ATBIs) coordinated by the European Distributed Institute of Taxonomy (EDIT), we analysed diatom communities colonizing different habitats of the Valasco Valley (Maritime Alps Natural Park). The aim of this research was to shed light on the diatom richness in an Alpine context through i) the collection of data concerning diatom communities inhabiting an unexplored watershed of the Maritime Alps Natural Park, including all of the most important aquatic habitats (comparison among river, springs and peat bogs) and assemblages (epilithic and epiphytic diatom communities); ii) analysis of the main environmental factors driving the development of diatom communities in different habitats. We completed a list of 174 diatom taxa. In general, river samples were poorer in terms of species richness than spring and peat bog ones, probably due to the selective role of the fast flow, while springs sheltered the highest biodiversity of the Valasco Valley. Peat bog communities were mainly composed of acidophilous taxa, sometimes planktonic and forming colonies. Epilithic and epiphytic samples did not show significant differences in terms of composition and biodiversity, even though it was statistically possible to identify indicator species for each assemblage. The study also highlighted the presence of several taxa included in the German Red List as endangered or decreasing, especially in the epiphytic samples. Since the water nutrient level and substrate geology were similar among habitats, the main environmental factors shaping Valasco diatom communities were water velocity and pH.