Boundaries

This ecoregion includes the entire Río Magdalena drainage system covering the eastern slopes of the Cordillera Occidental and Abibe Highlands, both slopes of the northern Cordillera Central, and western slopes of the Cordillera Oriental and Santa Marta Massif. It also includes the inter-Andean valleys of the Cauca and Magdalena rivers to the Colombian Caribbean coast, as well as the Sinu drainage.

Topography

The Magdalena drainage originated around 10 mya with the uplift of the Cordillera Oriental. The basin is surrounded by the Cordillera Occidental, Cordillera Central, and Cordillera Oriental of the northern Andes. The volcanic Santa Marta Massif rises from the coast in the northern part of the ecoregion with elevations that exceed 5000 m asl. The central portion of the Magdalena basin is dominated by a vast depositional basin called the “Momposina Depression” where the floodplain is very extensive and the landscape is dominated by floodplain lakes, locally refered as “cienagas”.

Freshwater habitats

The Magdalena, its largest tributary the Río Cauca, and the Río Sinú have high gradient headwater and upland streams and a few natural mountain lakes; upland main stems of the Magdalena and Cauca are turbid, shallow, and rocky.  A large proportion of the mountain streams have their origin in high elevation páramos. On the coastal plain moderate to broad floodplains occur along large river channels; the lower basins and coastal regions have extensive swamps, marshes, and lakes. The Momposina Depression at the confluence of the San Jorge, Cauca, Magdalena, and Cesar rivers contains lakes (ciénagas), swamps, marshes, and narrow channels.  Ciénega Grande de Santa Marta may be an old deltaic system of the Río Magdalena, bounded on the west by the mouth of that river and on the east by the Sierra Nevada de Santa Marta.

Terrestrial habitats

The terrestrial habitats are variable, ranging from the Magdalena-Urabá moist forests and Sinú Valley dry forests toward the coast to the Magdalena Valley montane forests and Cauca Valley montane forests on the slopes of the Eastern and Central Cordilleras, and the intermontane Magdalena dry forests and Cauca Valley dry forests. Northern Andean páramo occurs at the highest elevations.  Extensive areas of tropical cloud forest are also found at mid-elevations along the cordilleras.

Description of endemic fishes

The Magdalena basin contains many endemic fishes, most notably Eremophilus (Trichomycteridae), Genycharax (Characidae), Carlastyanax (Characidae), and Centrochir (Doradidae), which are endemic genera to the basin. Ichthyoelephas is another local genus, restricted to this ecoregion and the North Andean Pacific Slopes - Rio Atrato ecoregion [301]. The unique characid genus Grundulus is found in the upper Magdalena around the savanna of Bogota, whereas the monotypic Dupouyichthys sapito (Aspredinidae) is only shared with the Maracaibo basin.  Several genera have assemblages of endemic species in the basin, including Apteronotus, Astroblepus, Brycon, Bryconamericus, Chaetostoma, Creagrutus, and Hemybrycon. Cynopotamus magdalenae and Acestrocephalus anomalus (Characidae), Pseudopimelodus schultzi (Pseudopimelodidae), Xyliphius magdalenae (Aspredinidae), Eremophilus mutisii (Trichomycteridae), and Creagrutus caucanus and C. brevipinnis (Characidae) are endemic to the upper Río Cauca; C. magdalenae is endemic to the Río Magdalena; and C. nigrostigmatus is only known from Caño Pechilín, a small coastal stream west of the mouth of the Magdalena (Harold & Vari 1994).

Other noteworthy fishes

Mountain stream fishes (astroblepids, trichomycterids, loricariids, characids) live in Andean uplands and mountains.  This ecoregion shares some species (e.g., characids Creagrutus affinis and Roeboides dayi) with river systems in the westerly adjacent North Andean Pacific Coasts - Río Atrato ecoregion [301], and others (e.g., characid Gilbertolus alatus, ctenoluciid Ctenolucius hujeta, and pimelodid Sorubim cuspicaudus) with the easterly adjacent Maracaibo ecoregion [303] (Harold and Vari 1994; Vari 1995; Menezes and Lucena 1998; Littmann et al. 2000; Lucena 2000).

Ecological phenomena

Historically several species undertook large migrations, especially the prochilodontids Prochilodus magdalenae and Ichthyoelephas longirostris.

Justification for delineation

This ecoregion falls within the Magdalenean ichthyographic region exemplified in Gery (1969) and Ringuelet (1975). It contains a unique assemblage of species, high degree of endemism at the species level, and presence of several unrelated endemic genera.

Level of taxonomic exploration

Good