Boundaries

This ecoregion includes all the coastal drainages along South America’s western coast between the Río Sama drainage in southern Peru and the coastline south of Antofagasta in northern Chile. The eastern limit of this ecoregion is bordered by the Western Cordillera of the Andes.

Topography

The Atacama Desert lies between the Cordillera de la Costa and the Western Cordillera of the Andes in a crisscross network of hills and mountains. The highest elevations occur around a group of stratovolcanos, of which Aucanquilcha and San Pedro stand the tallest at 6176 m and 6145 m asl, respectively. The Cordillera de la Costa runs parallel to the Chilean coast between 18º and 28 º S, with an average elevation of 1500 m asl. It is composed of Mesosoic igneous and sedimentary rocks (Clarke 2006). Further inland is the Central Depression, which is a flat surface, interrupted by undulating hills formed by overlapping alluvial fans, and fluvial, lacustrine, and evaporitic deposits. To the east lies the Precordillera (also called the Cordillera Domeyko between 22º and 27 ºS) composed of a basement of Paleozoic sedimentary, igneous, and volcanic rocks (Moreno & Gibbons 2007).

Freshwater habitats

Convective air masses from the Amazon Basin bring precipitation to the Andes, resulting in runoff and groundwater that drain the Western Cordillera toward the Pacific Ocean via rivers and low-energy permanent (Quebrada Tana, Quebrada Guataguata) and intermittent (Quebrada la Higuera) streams called quebradas. High levels of groundwater support instream wetland vegetation along the beds of the perennial streams, as well as at the base of the Andes where basin aquifers intersect groundwater flow paths (Rech et al. 2003). Fed by snowmelt, the Río Loa is the longest permanent river (440 km), rising from the base of the Volcán Miño. Río Lluta originates at the Volcán Tacora, carving its path to the Pacific where it empties into an estuary near Arica. Toward the south the quebradas do not reach the ocean, but rather empty into inland basins such as the Pampa del Tamarugal (Santoro et al. 2005). In the central part of the Atacama, freshwater is restricted to brackish springs. The two Ramsar sites located in the Atacama ecoregion (Salar de Surire, Salar del Huasco) are salt marshes and brackish lagoons located in endorheic basins in the Andes (Wetlands International 2005). There are also salt flats in the Atacama, with Salar Grande being one of the oldest. In these systems water inflow is variable, and may originate from minor drainage systems, underground water, or springs, which may be thermal (Moreno & Gibbons 2007). In the eastern edge of the ecoregion is a geyser field called El Tatio, located around 4200 m asl in the Andes.

Terrestrial habitats

Vegetation of the Atacama Desert is concentrated around coastal hillsides that intercept a layer of fog that supports oases of vegetation known as lomas. These are fog-zone communities that develop on the seaward hillsides of the Cordillera de la Costa and along quebradas at low elevations (0-1100 m asl). Lomas communities comprise short-lived perennial and annual plants (Gramineae and Herbaceae) and woody scrub vegetation (Santoro et al. 2005). Tillandsia landbeckii is an air plant associated with lomas communities. However, much of the ecoregion is practically barren. Some of the few species in the northern desert zone include cacti such as Eulychnia iquiquensis and Copiapoa sp., which grow at elevations above 500 m (WWF 2001).

Description of endemic fishes

This ecoregion contains no strict endemic species.

Justification for delineation

This ecoregion forms part of the northern extension of the Chilean icthyographic province (from Río Rimac down to Río Loa) (Dyer 2000). It reflects a highly impoverished fauna due to the ecoregion’s hyper-aridity.

Level of taxonomic exploration

Fair