Distribution patterns of subaerial corticolous microalgae in two European regions

Abstract

Subaerial micro-algal biofilms growing on tree bark are omnipresent in a variety of ecosystems. However, terrestrial microhabitats have traditionally attracted far less attention from phycologists than marine and freshwater habitats, so their diversity and community structure is still very poorly known (Freystein & Reisser 2010, Rindi et al. 2010). Because of the lack of suitable discriminating characters and because species concepts are poor, species-level microscopic identification of most subaerial algae and Cyanobacteria is complicated (Ettl & Gartner 1995). In comparison to that of planktic and benthic communities, the morphological diversity of terrestrial microalgae is strikingly low; most taxa have coccoid spherical to oval cells, or simple filamentous thalli (Hoffmann 1989, Ettl & Gartner 1995). Consequently, most microscopic studies of subaerial assemblages have been based on either limited datasets acquired from approximate morphological identification of cultured strains (e.g. Nakano et al. 1991, Neustupa & Skaloud 2008), or direct observations of natural samples. Research on natural samples has typically been concentrated on several conspicuous groups, such as Trentepohliales, Klebsormidium, and Prasiola (e.g. Rindi & Guiry 2004, Hedenas et al. 2007). Recent molecular studies of subaerial microalgae have mostly been focused on phylogenetics and taxonomy of new and little-known microalgal and cyanobacterial lineages thriving in these microhabitats (Rindi et al. 2006, Zhang et al. 2008, Neustupa et al. 2013). They illustrated that the real phylogenetic diversity of subaerial microalgae was probably grossly underestimated by traditional morphological taxonomy. Molecular data revealed that the micro-algal communities of these habitats include numerous as yet unknown phylogenetic taxa. Some have been described as new micro-algal genera, such as Spongiochrysis, Heveochlorella, Hylodesmus, and Leptochlorella (Rindi et al. 2006, Zhang et al. 2008, Elias et al. 2010, Neustupa et al. 2013). Despite methodological limitations, microscopy still provides the very core of current knowledge on ecology and distribution patterns of subaerial algae, including those in corticolous biofilms. Tropical corticolous biofilms are often