Diversity of subaerial algae and cyanobacteria growing on bark and wood in the lowland tropical forests of Singapore

Background and aims - Knowledge on diversity and distribution of algae and cyanobacteria in subaerial habitats still lags behind those of freshwater and marine environments. Notably, data on diversity of microalgae in tropical corticolous habitats are still scarce. We investigated species composition of subaerial epixylic algae and cyanobacteria from two Singaporean rainforest localities. We asked whether there are differences in species composition and alpha-diversity of samples taken in different areas and in different habitat types (bark vs. decaying bare wood). In addition, we asked whether there are differences in species turnover (beta-diversity) among different habitat types and areas. Methods - The cultivation-based approach and the microscopic analysis of populations were used. In total, 20 samples of bark and decaying wood from two forested areas were analyzed. Statistical analyses involved the non-metric multidimensional scaling (NMDS) of species data. Significance of differences in algal composition between groups of samples was evaluated by the non-parametric two-way ANOSIM (Analysis of Similarities) using the crossed design with permutations in blocks. The SIMPER method was used to identify species that characteristically discriminate between habitat types and sampling areas. Key results - In total, 57 species were identified. Green algae (Trebouxiophyceae, Chlorophyceae, Trentepohliales) were dominant, and Cyanobacteria were the second most frequent group. The dominants of the subaerial assemblages differed from corresponding temperate habitats and, in addition, their alpha-diversity was considerably higher. Several green algal morphospecies were characteristic for the bark localities (e.g. Diciyochloropsis spp., Pseudomarvania aerophytica, Printzina effusa and Printzina lagenifera). The alpha-diversity was similar in both habitat types, but the species turnover among samples (beta-diversity) was significantly higher in the decaying wood samples. Conclusions - Tropical corticolous habitats probably harbour higher diversity than corresponding temperate habitats. High beta-diversity of decaying wood illustrates general importance of this substrate for biodiversity of subaerial algae in the tropics.