Boundaries

This ecoregion includes the entire drainage basin of the Rio Parnaíba and coastal drainages as far west as the Rio Munim drainage in Maranhão along São Marcos Bay.

Topography

The Parnaíba rises in the Serra da Tabatinga and flows in a northeasterly direction to the Atlantic Ocean. The Chapada das Mangabeiras, which divides the Parnaíba from the Tocantins basin, forms the western border. The eastern border of the ecoregion is flanked by the Serra da Ibiapaba, which runs north-south from near the Atlantic Ocean inland to the Serra Dois Irmãos. Elevations range from sea level to more than 900 m asl in the Serra da Ibiapaba. Crystalline and sedimentary soils characterize the upland areas whereas alluvial deposits are found at lower elevations.

Freshwater habitats

The Parnaíba basin is one of the largest basins in northeastern Brazil. Most tributaries below Teresina are perennial and fed by pluvial sources. However, a majority of the Parnaíba’s right bank tributaries are temporary, resulting in a lower average discharge rate (1272 m³/s) than other rivers in Brazil (Marques et al. 2004).

Terrestrial habitats

Terrestrial habitats in the ecoregion range from cerrado, which was once extensive throughout much of the Central Brazilian Plateau, to Atlantic dry forests and caatinga in the east along the western slopes of the Serra da Ibiapaba. Gallery forests line rivers and streams. Lower elevations are dominated by Maranhão Babaçu forests, which form a transitional area between the humid forests of the Amazon Basin and the drier cerrado of the Central Plateau. Mangroves and restingas line the coast.

Description of endemic fishes

There are no endemic genera in the ecoregion. However, more than 20% of the species are endemic. Characids, cichlids, and loricariids each contain three endemics. These are followed by anastomids and callichthyids with two species each, as well as some families with single endemics, such as the catfish Auchenipterus menezesi, Hassar affinis, and Pimelodella parnahybae, and the Parnaíba River stingray (Potamotrygon signata).

Other noteworthy fishes

Nearly half of the species within the Parnaíba ecoregion also occur within the Amazon lowlands ecoregion [316].

Ecological phenomena

The piraíba (Brachyplatystoma filamentosum) and Laulao catfish (B. vaillantii) are known for their spawning migrations.

Justification for delineation

This ecoregion straddles the Amazon and East Brazilian ichthyographic regions outlined by Gery (1969) and Ringuelet (1975).

Level of taxonomic exploration

Good