Substrate roughness affects stream benthic algal diversity, assemblage composition, and nestedness

v. 30, n. 4, p. 1049-1056, 2011Heterogeneity generated by irregularities on the surface of streambed substrates is animportant determinant of local species diversity of algae. However, few investigators have examined theeffects of substrate roughness on the composition of algal growth forms and on patterns of speciesdistribution. We examined the influence of substrate roughness on stream benthic algal assemblagesthrough a field experiment with 2 treatments (smooth and rough artificial substrates for algal colonization).We assessed whether species richness, density, and assemblage composition of benthic algae (all taxaand those in 5 growth-form groups) differed between treatments and whether differences in speciescomposition between substrates were the result of species turnover or nestedness. We also used a datasubsampling procedure to investigate the effect of differences in species richness between treatments. Totalspecies richness was higher on rough than on smooth substrates, but density did not differ betweentreatments. Species richness, density, and composition of the adnate/prostrate growth form did not differbetween treatments. The erect/stalked growth form had higher species richness on rough substrates,but did not differ in density between treatments. All other growth forms (filamentous, motile, andmetaphyton) had higher species richness and density on rough substrates and differed in speciescomposition between substrates. The results of the subsampling analysis indicated that assemblagecomposition was affected by differences in species richness and by changes in species composition (i.e.,turnover). Species distribution had a nested pattern, in which the assemblages on smooth substrates were asubgroup of the species occurring on rough substrates. We suggest that the differences in assemblagecomposition between smooth and rough substrates resulted from variability in species’ capabilities tocolonize substrates with or without crevices. This variability resulted in both nestedness and turnover