Abstrait

Structure and Dynamics of Benthic Macroalgae Communities in Lotic Ecosystems Under the Effect of Uneven Topography

Rogério Antonio Krupek

This study aimed to assess the effects of topographical gaps (waterfalls) of different proportions on the ecological characteristics and composition of benthic macro algae communities present in a lotic system. In this sense, the biotic (composition, richness, abundance, diversity, dominance and evenness) and abiotic (physical and chemical characteristics of water) characteristics were assessed in three topographical gaps of different proportions (2.80, 6.5 and 40 meters high). The analyses were made in a pre-established segment before and after each waterfall. Eight benthic macro algae taxa (50% belonging to the Cyanobacterial division, 37.5% to the division Chlorophyta and 12.5% to the division Heterokontophyta) were found. The floristic composition was similar both in different waterfalls and in different points of the same waterfall, which is due to the low occurrence of taxa, in addition to the wide distribution of some species (i.e., Phormidium retzii). Among the ecological parameters of communities, differences were found between the waterfalls (as to species richness and abundance, evenness and diversity index) and between different points of the same waterfall (abundance). The biotic variable most affected by micro-environmental variables (substrate size, depth and current speed) was the abundance of species. Thus, the presence of topographical gaps in the streambed or riverbed directly interfered, mainly, in the structure of benthic macro algae communities assessed, acting as a physical barrier and creating the specific conditions for the development of diverse communities in segments with similar lotic environments.