Abstract
This study investigated the structure of the Oligochaeta and Chironomidae assemblages associated with monospecific stands of two submerged macrophyte species: Egeria najas and Hydrilla verticillata. Samplings were carried out in Leopoldo Backwater and Parana river, in August 2008. To assess the structure of Oligochaeta and Chironomidae assemblage in each macrophyte we calculated: species density, richness, diversity, and evenness. A detrended correspondence analysis (DCA) was used to summarize Oligochaeta and Chironomidae assemblages composition. The highest values of species density and richness for the two groups were recorded in H. verticillata. Although there were no significant differences in density, richness and Shannon diversity, the assemblage composition of these groups was significantly different between plant species. These results suggest that despite being a recent colonizer in the upper Parana river habitats, the non-native species H. verticillata seems to provide favorable conditions for the establishment of native assemblages of Chironomidae and Oligochaeta. Moreover, differences in the species composition of Oligochaeta and Chironomidae arose from peculiar characteristics of each plant, as attached microorganisms and organic matter, so that other factors, rather than plant architecture can also influence the assemblage of these groups.
Highlights
Aquatic macrophytes assemblages play important roles in freshwater environments (PELICICE et al, 2005; THOMAZ et al, 2008), since they affect resources partitioning (MCCOY; BELL, 1991; CAMPEAU et al, 1994), promote changes in bioticActa Scientiarum
The values of limnological variables presented a slight variation between the macrophyte stands, except for CO2 total and turbidity (Table 1). The latter was higher in Egeria najas stands, because this plant was collected in the entry of the backwater, while Hydrilla verticillata was collected in stands in the Paraná river, which presents clear water
Allonais paraguayensis and Stylaria lacustris were only recorded in H. verticillata, whereas P. americana was exclusive for Egeria najas
Summary
Aquatic macrophytes assemblages play important roles in freshwater environments (PELICICE et al, 2005; THOMAZ et al, 2008), since they affect resources partitioning (MCCOY; BELL, 1991; CAMPEAU et al, 1994), promote changes in bioticActa Scientiarum. The plants structure influences the colonization by those organisms, with more intense colonization in the plants that show higher structural complexity (JACKSON, 1997; CHERUVELIL et al, 2002; DIBBLE et al, 2006). In this way, distinct aquatic macrophyte communities will sustain different invertebrates communities (THORP et al, 1997; MELO et al, 2002; TAKEDA et al, 2003). The habitat selection process is not well understood, and probably involve several mechanisms, since simpler ones, as the presence or absence of predators (RESETARITS, 2005) and resources availability (DE HAAS, 2006) to more complex ones, as physical and/or chemical barriers that prevent colonization (DE HAAS, 2006)
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