This paper aimed to describe the successional changes in the structure of periphytic algal assemblages in a lotic environment, during the rainy period, indicating the descriptor species. The study site was Corvo stream (22º39'S, 52º46'W), a tributary of the Paranapanema river, located near the Rosana Reservoir, in the northwestern Paraná state, Brazil. Periphyton samples on artificial substrate and abiotic data were obtained from 21 November to 12 December 2003, at three-days intervals. Algae were identified and quantified using inverted microscope at 400X, according to Utermöhl. The analysis of the succession dynamics considered the following parameters: species richness, total density, relative abundance of taxa, descriptor species, Shannon-Wiener diversity and evennes. Fluctuations in total density were determined mainly by Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Zygnemaphyceae. Higher values of abundance of the periphytic algae were recorded for small species of diatoms, known as efficient colonizers, which were abundant throughout the study period and showed rapid growth, as well as for Cyanobacteria and filamentous green algae (Oedogonium spp. and Stigeoclonium spp. ), which were more abundant in the latter successional stages and showed slower growth. The first ones are among the r-strategists, while the latter are among the C-S strategists (more competitive algae in mesotrophic and stable systems). Shannon-Wiener diversity was high (2.2 to 3.1), with the highest value in the third week of study. According to the principal components analysis, nutrients concentrations, pH and turbidity were the most important abiotic factors for explaining the community structure changes throughout the succession.
community structure; diversity; periphyton; river; succession
