Estrutura da comunidade de algas perifíticas em distintos substratos naturais da planície de inundação do alto rio Paraná, Brasil.

Abstract

Structure of periphytic algae community in different natural substrates (Eichhornia azurea Kunth, Nymphaea amazonum Martius and Zuccarini and Oxycaryum cubense (Poeppig and Kunth) Lye) was analysed in a semilotic environment permanently connected to the Paraná River, from the Upper Paraná River floodplain. Samples were quarterly collected from June/2008 to March/2009, from these three macrophytes which were scraped for removal of periphytic community. Limnological data from the study site were concomitantly obtained. The year 2008 was characterized by the irregularity of flood pulses, water levels and hydrological periods of the Paraná River. Homogenizing effect could be observed only for connected environments, such as the "Pau Véio" backwater. It was not possible to distinguish the characteristic periods of high water and low water. We found 406 taxa of periphytic algae. The most representative classes corresponded to Bacillariophyceae, Zygnemaphyceae, Cyanobacteria and Chlorophyceae. Taxonomic similarity based on specific composition during sampled periods and substrates showed a distinction mainly among sampled months, which June/2008 differed significantly from the others. Differences in composition of periphytic algae between the substrates were not pronounced and were due mainly to O. cubense. A total of 31 dominant taxa in the different periods and substrates have been described and illustrated, which 23 taxa constituted firstly taxonomic citations for the Upper Paraná River floodplain. O. cubense detained the highest species richness of periphytic algae, followed by E. azurea, however the mean values for this attribute were not significantly different. Substrate which included the highest average algal density corresponded to E. azurea, which has the stronger architecture and morphology favoring the growth of periphytic algae, mainly diatoms. Nymphaea amazonum occupied an intermediate position, while O. cubense, presented the lowest densities, because its more delicate architecture and fragile morphology, favoring mainly metaphytic algae such as taxa belonged to the class Zygnemaphyceae. Diversity values were high for all substrates, with significant oscillations in E. azurea, highlighting to importance of substrate diversity for periphyton. When considering period, the highest richness occurred in November 2008 and March 2009 and the opposite occurred to density, with lower values in these periods. In June 2008, the class Bacillariophyceae was prevalent (predominantly represented by Achnanthidium minutissimum), followed by Cyanobacteria, both for richness as density. This fact represents the greater tolerance of these algae during stressing periods, such as lack of nutrients and low temperatures occurred in June 2008, because of their greater competitive advantage towards other algal groups. November 2008 and March 2009 were characterized by the highest mean values of water levels and higher temperatures, which may have influenced the environment through the input of propagules and the establishment of a greater number of taxa during the disturbance event. Low taxonomic similarity and significant divergences in density and diversity of periphytic algal community demonstrated primarily the temporal and, secondarily but less pronounced, the spatial segregation of periphytic algae. These differences were due primarily to daily fluctuations of hydrometric levels wich characterize the sampled months, consequently confering variability to the limnological characteristics in environment. Morphology and architecture of macrophytes promote an environment with specific conditions, which secondarily influenced periphytic algae community. Architecture of O. cubense was probably responsible for the largest differences between periphyton communities among different substrates, because morphology of stem and leaf sheath which provides a differential microhabitat. E. azurea and N. amazonum present petiole morphologies apparently more similar.