Boundaries

This ecoregion includes the Iguaçu River basin and all its tributaries, from its headwaters to Iguaçu (Iguassu) Falls.

Topography

The Rio Iguaçu rises in the Serra do Mar and travels across the Paraná Plateau before dropping off the plateau at Iguaçu Falls near its confluence with the Paraná River. Elevations vary between 136 m and 1350 m asl, and average around 800 m (Hijmans et al. 2004). The ecoregion lies on sedimentary and basaltic rocks of the Paraná Plateau, with the main channel of the Rio Iguaçu flowing through a fault. Soils throughout the ecoregion range from fertile latosols to impoverished lithosols (WWF 2001).

Freshwater habitats

Rio Iguaçu meanders across the Paraná Plateau, encountering numerous rapids and falls along the way before its precipitous drop at Iguaçu Falls, which lies at the border of Brazil and Argentina. The Iguaçu Falls comprise 275 cascades, the most notable of which is the Devil’s Throat at 82 m in height, 700 m in length, and 150 m in width.  Tributaries and small headwater streams are mostly of moderate slope and cut through sandstone rocks.

Terrestrial habitats

The subtropical Araucaria moist forests cover this ecoregion in a complex of trees that include emergent Brazilian Araucaria (Araucaria angustifolia), Brazilian sassafras (Ocotea pretiosa) O. catharinense, gabiroba (Campomanesia xanthocarpa), and angico (Parapiptadenia rigida).  These forests are a relict of a once widespread ecosystem of mixed coniferous and broad-leafed trees (WWF 2001).

Description of endemic fishes

There are presently 39 endemic species representing more than 61% of the fish in the basin. There is also one endemic monotypic genus, Psalidodon (P. gymnodontus). Although this is currently recognized as a distinct species (Eschmeyer 2010), it has recently been re-described as a synonym of Astyanax gymnodontus (Pavinelli & Oliveira 2009). The high endemism in the basin is attributed to multiple cascades and the formidable Iguaçu Falls, which have provided effective barriers to dispersal between the Paraná and Iguaçu (Garavello et al. 1997 in Pavinelli & Oliveira 2009).

Other noteworthy fishes

Some groups that are absent in this ecoregion include Clupeiformes, Pleuronectiformes, several families of Characiformes and Siluriformes, and the genera (Piaractus, Brycon, Serrasalmus, Pseudoplatystoma, etc.), which are otherwise common throughout the Paraná basin.

Ecological phenomena

Large migratory fish are absent in the Iguaçu River, with the exception of Steindachneridion melanodermatum, which is restricted to the lower river (Agostinho et al. 2003).

Justification for delineation

This ecoregion falls within Gery’s (1969) Paranean region, and Ringulet’s (1975) Paraná-Platense icthyofuanistic province. The Iguaçu River basin has been isolated from the Paraná for more than 22 million years by the Iguaçu Falls and other cascades, resulting in speciation and high endemism (Agostinho et al. 2003; Garavello et al. 1997 in Pavinelli & Oliveira 2009).