Boundaries

This ecoregion includes all of the independent rivers running off the northern and eastern slope of the Guiana Shield into the Atlantic Ocean, from the Demerara River (Guyana) to the Oyapock (French Guiana and Brazil). It is limited to the south by the Amazon drainage divide.

Topography

This ecoregion lies on coastal lowlands of the Guiana Shield and is predominantly flat. Highlands include the Wilhelmina, Bakhuis, Van Asch Van Wijck, Kayser, Oranje, Lely mountain ranges in Suriname. The highest elevation is at Juliantop at 1286 m asl in the Wilhelmina Mountains.

Freshwater habitats

Freshwater habitats in the highlands range from moderate gradient small streams to rivers with rapids and some cataracts. Along the coastal plains are low gradient rivers, lakes, and swamps with seasonal flooding.

Terrestrial habitats

Guianan moist forests dominate the landscape with species such as andiroba (Carapa guianensis), kapok (Ceiba pentandra), cannonball tree (Couroupita guianensis), and oil tree (Pentaclethra macroloba). Between the moist forests and coastal mangroves lie permanently inundated swamp forests that stretch from the Corantijn River to the Marowijne River.

Description of endemic fishes

Endemism in the ecoregion is high with nearly nearly 40% of the species restricted to this ecoregion. Families with the largest number of endemics include Loricariidae, Characidae, Callichthyidae, and Cichlidae. Endemic genera include the monotypic Scissor, Derhamia, and Harttiella. Propimelodus was once considered endemic to this ecoregion, but two new species (P. araguayae and P. caesius) have recently been identified elsewhere in the Amazon Basin.

Other noteworthy fishes

The ecoregion contains 18 gymnotoid species, all of which have electrogenic or electro-sensory organs; the largest is the electric eel (Electrophorus electricus).

Ecological phenomena

The ecoregion contains the potamadromous barred sorubim (Pseudoplatystoma fasciatum).

Justification for delineation

This ecoregion lies in the Guyanan ichthyographic province outlined in Ringuelet (1975) and more broadly within the Guyanan-Amazonian ichthyographic  region (Gery 1969). It contains a unique assemblage of species with high endemicity along the northern slopes of the Guiana Shield.

Level of taxonomic exploration

Fair in general, poor in the upper portions of the basins.