Factors affecting assemblage attributes of freshwater Oligochaeta in Neotropical shallow floodplain lakes

Aim: Identify the effects of sediment composition and water conditions on diversity, richness, evenness, density and composition of freshwater Oligochaeta in shallow floodplain lakes. Methods: We sampled 13 shallow floodplain lakes quarterly during the year 2010 in the Upper Parana River floodplain. In each lake, four sediment samples were taken from the shore and central regions, three of them were used for biological analysis, and one for granulometric analysis. Concomitantly, temperature, dissolved oxygen, pH, conductivity, alkalinity, turbidity and chlorophyll-a were also measured. Initially, the biological samples were analyzed by a stereoscopic microscope and Oligochaeta specimens were picked up. Oligochaeta individuals were identified under optical microscope at the lowest possible taxonomic level. For data analysis, we quantified density, richness, evenness and diversity of freshwater Oligochaeta. We also calculated the sediment granulometric diversity using the Shannon-Wienner method. We correlated assemblage attributes of Oligochaeta with sediment diversity and the Oligochaeta species with the limnological variables using the Spearman correlation. Results: A total of 2,090 specimens were found distributed among 27 species. From the total specimens number, 57% were Pristina americana , followed by Dero Dero righii with 13%. We did not fond Oligochaeta specimens in five lakes. Assemblage attributes were not significantly correlated with sediment diversity, and 7 of the 27 species recorded showed significant correlations with at least some of the abiotic variables. Conclusions: We verified a greater contribution of water conditions on the assemblage attributes of freshwater Oligochaeta, when compared with sediment influences. Although we found low local diversity of Oligoachaeta, the wide range of water conditions offered by lakes culminates with a great species richness considering the whole landscape.