Boundaries

This ecoregion includes the drainage basin of the upper Rio Paraná and its tributaries above the former Guaíra Falls (Salto de Sete Quedas). Although this represents the historical divide, the Itaipú Reservoir above the Itaipú Dam is also incorporated. The ecoregion is bounded to the north, east, and south by the Central Brazilian and Coastal Highlands, with the general slope of the basin draining to the south-southwest. The ecoregion lies almost entirely within the borders of Brazil, except for the southwestern edge, which lies in Paraguay.

Topography

The upper Paraná is part of a sedimentary basin bordered by Precambian rocks of the Central Brazilian Highlands and Coastal Brazilian Highlands to the north and east (Lundberg et al. 1998). Elevations extend from around 120 m to over 1500 m asl in the Serra da Mantiqueira (Hijmans et al. 2004). The landscape is marked by plateaus, rolling hills, and deeply cut valleys (Resende 2004).

Freshwater habitats

After the Amazon the Rio Paraná is the second largest river in South America, and forms part of the second largest basin, the La Plata basin. It lies on the Guaraní Aquifer, one of the largest aquifer systems in the world.  The upper Paraná extends from the confluence of the Paranaíba and Grande rivers, which rise from the Serra dos Preneos and Serra da Mantiqueira. These rivers flow through foothills, and are interrupted by rapids and waterfalls (Bonetto 1986a). Many of the waterfalls occur close to the confluences of tributaries and the main stem of the Paraná. Some of the large right bank tributaries like the Ivinheima, Iguatemi, and Amambai rise from springs from the sedimentary basin and tend to be short and meandering with a low slope and sandy bottoms. In contrast, left bank tributaries like the Piquiri, Ivai, and Tietê rise from springs in the crystalline rocks of the Serra do Mar and tend to be long and rapid with steep slopes and rocky bottoms (Agostinho et al. 2003).  The riverbed of the main channel of the Paraná is rocky with patches of sedimentary soils, although between the Porto Primavera Dam and Itaipu Reservoir the bottom is sandy (Agostinho et al. 2003; Resende 2004). Spawning habitats occur in both rocky and sandy bottoms of the upper and lower parts of tributaries like the Piquiri and Ivinheima, as well as along the main stem of the Paraná. The floodplain along the lower part of the upper Paraná includes anastomosing channels, sandbars, small and large islands, and lagoons. The lagoons provide nursery habitats for many species, and contain particularly diverse assemblage of phytoplankton, zooplankton, aquatic macrophytes, rotifers, periphyton, and fishes (Agostinho et al. 2003).

In contrast to the lower Paraná, the upper Paraná has a lower conductivity (40-50 (µS/cm), lower total suspended solids (between 40-180 mg/l), and lower pH (7-7.2). Discharge levels peak in January/February, and are lowest in August/September at the end of the dry season (Quirós et al. 2007). It is also characterized by high silica and low calcium concentrations (Bonetto 1986a).

Despite its exceptional diversity, the upper Paraná and its tributaries have undergone extensive modifications for flood control and hydroelectric power. As a result only small areas of the natural floodplain remain. In the southern part of the ecoregion the floodplain may reach up to 20 km in width.

Terrestrial habitats

The terrestrial habitats in the ecoregion range from cerrado in the north to the moist Atlantic coastal forests in the south and east. In between lies the Alto Paraná Atlantic forests ecoregion, which is a semi-deciduous forest region that is transitional between the drier cerrado and moist forest habitats. Here, canopy trees are dominated by species from the families Lauraceae, Apocynaceae, and Leguminosae. Gallery forests and flooded grasslands border the larger rivers (World Wildlife Fund 2001).

Description of endemic fishes

Although the number of fish species recorded from the upper Paraná is lower than the lower Paraná (around 340 species), the number of endemics is more than two and a half times as high. Presently there are 131 endemic species and seven endemic genera recorded from the upper Paraná. The families Characidae, Loricariidae, and Rivulidae contain the highest number of endemic species. The six endemic genera are all monotypic, and are represented by the species Aphyocheirodon hemigrammus, Coptobrycon bilineatus, Lophiobrycon weitzmani, Tembeassu marauna, Microlepidogaster perforatus, and Otothyropsis marapoama.  Rhinolekos is represented by three species. Rapids and waterfalls that occur along the main stem and tributaries limit fish distributions upstream, contributing to the high level of endemism in the ecoregion (Resende 2004).

Ecological phenomena

The upper Paraná is home to a number of species that migrate up to hundreds of kilometers to spawn during spring floods. The streaked prochilod (Prochilodus lineatus) – also known as curimbatá or sábalo – covers some of the longest distances. Other migratory species include the tabarana (Salminus hilarii), dorado (Salminus brasiliensis) piavuçu (Leporinus obtusidens), biara (Rhaphiodon vulpinus), and pacu (Piaractus mesopotamicus) (Characiformes); and spotted sorubim (Pseudoplatystoma corruscans), granulated catfish (Pterodoras granulosus), and cascudo-preto (Rhinelepis aspera) (Siluriformes).

Justification for delineation

The upper Paraná north of the Guaíra Falls is a region of high endemism. It falls within Gery’s (1969) Paranean region, and was further refined by Ringulet (1975) as the Upper Paraná icthyofuanistic province (Bonetto 1986b).

Level of taxonomic exploration

Good across most of the geography.