Abstract
Abstract The drainages of the Iguaçu River basin, as well as the main channel of the river, have peculiar characteristics resulting from geomorphological processes in this area, including the formation of the Iguaçu River Falls. This slope in the lower portion of the basin is a biogeographical barrier to many organisms. In this study was inventoried the fish fauna of streams of the lower Iguaçu River basin, evaluating possible differences in the species composition upstream and downstream of this biogeographical barrier. Sampling were conducted between 2004 and 2013, in five streams, three upstream and two downstream of the Iguaçu River Falls, using electrofishing. The nMDS analysis was run to investigate possible groupings of similar fauna between the streams sampled. The scores of this test were tested as to the significance of groupings with the Hotelling T2 test. The indicator value method (IndVal) was used to detect the distribution of species among the groups of the streams upstream and downstream of the Iguaçu River Falls. We collected 18,908 individuals of six orders, 11 families, and 40 species. Siluriformes and Characiformes had the highest species richness; Cyprinodontiformes presented the highest abundance. Considering the species recorded, 21 are considered natives to the Iguaçu River basin, including 15 endemic, wich were found only in streams upstream of the falls. Additional 18 species were verified only in the streams downstream of such barrier. Four species were common to both stretches. The axis 1 of the nMDS separated two groups: streams upstream (S1, S2 and S3) and streams downstream of the Iguaçu River Falls (S4 and S5). The indicator species analysis also indicated a distinction between the groups of streams, that were significantly different (Hotelling's T2 = 234.36, p ˂ 0.0001). The number of endemic species in the streams upstream of the Falls (15 spp.) evidences a significant effect of isolation promoted by the Iguaçu River Falls, and confirms the role of this barrier in the vicariant processes and endemism typical of this basin. These results emphasize the importance of conserving these ecosystems, once the extinction of species in this region means the irreversible loss of them.
Highlights
The Paraná State, Southern Brazil, has 16 basins (Parolin et al 2010), including the Iguaçu River basin, formed by the longest river in the Paraná State with approximately 1,080 km (Garavello et al 2012)
The Iguaçu River and its tributaries features a fauna of small-sized fish, with a high degree of endemism (Vicari et al 2006), possibly due to the geographical isolation given by the Iguaçu River Falls that isolated this river from the lower Paraná River basin (Baumgartner et al 2012)
The number of species observed in this study (40 spp.) can be considered high, especially if evaluated some issues: (i) the number of species recorded for other water bodies with similar size in the Neotropics (Bertaco 2009, Couto & Aquino 2011, Marceniuk et al 2011, Oyakawa & Menezes 2011, Cetra et al 2012, Daga et al 2012), as well in other streams in the Paraná State (Araújo et al 2011, Delariva & Silva 2013, Gubiani et al 2010); (ii) the proportion of species registered represents 37.7% of the total number of species recorded for the Iguaçu River basin (106 spp.), including those observed in the main channel of the river (Baumgartner et al 2012)
Summary
The Paraná State, Southern Brazil, has 16 basins (Parolin et al 2010), including the Iguaçu River basin, formed by the longest river in the Paraná State with approximately 1,080 km (Garavello et al 2012). Considering the confluence of the Atuba and Iraí rivers as its origin, the Iguaçu River runs in the east-west direction from its headwaters in the Serra do Mar to its mouth on the Paraná River (Baumgartner et al 2012). Along its course, it crosses different geological and geomorphological units, with an altitude range of 830 m, considered as a typical plateau river, with numerous rapids and falls. The Iguaçu River and its tributaries features a fauna of small-sized fish, with a high degree of endemism (Vicari et al 2006), possibly due to the geographical isolation given by the Iguaçu River Falls that isolated this river from the lower Paraná River basin (Baumgartner et al 2012)
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