Composition of biological soil crusts from sand dunes of the Baltic Sea coast in the context of an integrative approach to the taxonomy of microalgae and cyanobacteria

Abstract

Most of the data on biodiversity, ecology and biogeography of microalgae and cyanobacteria are based on classical morphological approaches. However, morphological identification of these microorganisms is often possible only to higher taxonomic ranks such as genus, because of low morphological diversity and high variability along with the presence of cryptic taxa. This study compared the species composition of cyanobacteria, and green and streptophyte microalgae, isolated from biological soil crusts (BSCs) of maritime sand dunes (Baltic Sea, Germany) and identified through culture-dependent morphological methods combined with molecular phylogenetic data. Phylogenetic analyses (based on SSU rRNA and ITS-1,2 for microalgae, or the SSU-LSU ITS region for cyanobacteria) provided unambiguous identifications of 20 strains (37.7% of all strains investigated) to species level; the identifications had to be corrected after preliminary morphological determination of eight strains. For 27 strains (50.9%), identification with molecular markers was possible only to genus or group of closely related species, because a modern taxonomic revision of these taxa is preliminary, incomplete or non-existent. Identification to genus was problematic for six strains (11.3%). This combination of morphological and molecular methods (integrative approach) resulted in the discovery of rare, taxonomically or ecologically interesting taxa, and in the description of a new species of Tetradesmus (T. arenicola sp. nov.), a new combination for Chlamydomonas callunae (Heterochlamydomonas callunae comb. nov.), epitypification of the rare alga Actinochloris sphaerica and emendation of the recently described Eremochloris sphaerica. A microscopic culture-dependent method and an integrative approach provided similar results concerning the cyanobacterial and algal diversity of BSCs of Baltic sand dunes in general. However, this investigation using an integrative approach allowed us to precisely identify species of several important taxa (the most common and dominant species) in the community structure of BSCs, and also certain rare representatives.