Boundaries

This ecoregion includes all of the Pacific coastal drainages of Peru from Punta Mal Nombre south of the Río Piura drainage divide in the north, to the Río Locumba drainage in the south. The ecoregion is bordered to the west by the Pacific Ocean and to the east by the Western Cordillera of the Andes.

Topography

The Central Andean Pacific Slopes ecoregion extends from the flat plains, dunes, and low hills of the Sechura Desert along the coast up to the Western Cordillera, with its towering peaks that exceed 6000 m asl. Nevado de Huascaran in the snowcapped Cordillera Blanca of Peru is the highest peak at 6768 m asl, and nearby Huandoy is nearly 6400 m. Nevado Coropuna (6425 m), Nevado Ampato (6288 m), and Nevado Solimana (6117 m), stratovolcanos in the Central Volcanic Zone, also rise above 6000 m.

The landscape is scarred by the Colca and Cotahuasi canyons, both of which are twice as deep as the Grand Canyon. Cotahuasi Canyon (3535 m) is formed by the Río Cotahuasi (a tribuatary of the Río Ocoña) and the Colca Canyon (3400 m) is cut by the Río Colca.

Soils throughout the ecoregion are dominated by lithosols, which are shallow soils consisting of imperfectly weathered rock fragments. Eutric regosols and eutric fluvisols occur along the coastline, and andosols are common in the south along the Central Volcanic Zone (FAO 2003).

Freshwater habitats

The arid coastal plain is cut by more than fifty short rivers. Many are barely developed, and only a few are perennial (Lundburg et al. 1998). Most runoff is due to seasonal rainfall on the western slopes of the Cordillera Occidental of the Andes. During periods of drought, many of the rivers, like the Río Jequetepeque, are irregular with flows less than 1.0 m³/s. In contrast, Río Ocoña has considerable flow. This is reflected in the deeply cut Cotahuasi Canyon through which the Río Cotahuasi, a tributary of the Río Ocoña, flows.

Along the coast are wetlands, including several Ramsar sites, such as the Los Pantanos de Villa near Lima and Santuario Nacional Lagunas de Mejía near the mouth of the Río Tambo. These are saline and brackish lagoon systems that provide important habitats for migratory birds from both North America and the Andes, as well as important breeding areas for resident birds (Wetlands International 2005).

Salt lakes, such as the Ramsar site Bofedales y Laguna de Salinas, occur at high elevations (Wetlands International 2005). Other high-altitude freshwater systems include glacier lakes like Laguna Parón in the Cordillera Blanca.

Terrestrial habitats

This ecoregion encompasses the Sechura Desert, which extends from 20 to 100 km inland. Vegetation is scarce, although the flora includes various species such as pájaro bobo (Tessaria sp.), tillandsiales (Tillandsia sp.), beach grasses, grama salada (Distichlis spicata), verdolaguilla (Salicornia fruticosa), and endemics such as Tropaelun peltophorum, Drymaria weberbaueri, and Dioscorea chancayensi (WWF 2001).

The more abundant vegetated areas include riparian vegetation along river valleys and lomas vegetation that occurs in the fog-zone along seaward slopes of the Coastal Range between roughly 600-900 m asl (Péfaur 1982). Lomas are fog-zone plant communities comprising annual and short-lived perennial species and woody scrub vegetation. Some more conspicuous species include the Peruvian papaya (Carica candicans), pallilo (Capparis prisca), tara (Caesalpinia spinosa), and nettle (Loasa urens) (WWF 2001). These communities exhibit high endemism due to their isolated mesic populations and adaptations to desert conditions (Péfaur 1982).

Description of endemic fishes

There are presently 17 endemic species recorded in the ecoregion. More than half of the endemics are Siluriformes, followed by Characiformes and Cyprinodontiformes.

Other noteworthy fishes

In addition to the species restricted to this ecoregion, another 17 species are restricted to two ecoregions, bringing the number of endemics and near-endemics up to 80% of the population. For example, Basilichthys archaeus, B. semotilus, and Trichomycterus punctulatus only occur in the Central Andean Pacific Slopes and Atacama [338] ecoregions. Others, like the green terror (Andinoacara rivulata) and Guayas cichlid (Cichlasoma festae), are restricted to the Central and North Andean Pacific Slopes [336, 301] ecoregions.

Orestias is a genus of pupfish that occurs in the high altitude lakes of the altiplano. Although Lake Titicaca houses the largest number of endemic pupfish, this ecoregion contains several, including two endemics, Orestias elegans and O. ututo.

Juveniles of the marine species Odontesthes regia has been found in estuarine environments (Dyer 2000).

Justification for delineation

This ecoregion crosses two of Gery’s (1969) faunal regions -- Trans-Andean icthyographic region along the northern Peruvian coast and Andean region along the southern coast -- indicating an impoverishment in the fauna as one moves from north to south due increasing aridity. Ringuelet (1975) further divided the Trans-Andean icthyographic region, with this ecoregion lying in the Guayas (in el Del Pacífico o Trasandino) icthyographic province. The southern part of the ecoregion forms part of the northern extension of the Chilean icthyographic province (from Río Rimac south to Río Loa) according to Dyer (2000).  It contains a unique and highly endemic assemblage of species.

Level of taxonomic exploration

Good