Boundaries

This coastal ecoregion stretches all the way from the Golfo de Tehuantepec in Oaxaca, Mexico to the Choluteca basin at the Golfo de Fonseca in southern Honduras. It encompasses numerous rivers on the southern slopes of the Continental Divide that drain into the Pacific Ocean.

Topography

This ecoregion lies to the southwest of the Continental Divide, and includes a narrow alluvial plain, a piedmont region, and a mountainous volcanic belt. Elevations range from sea level to nearly 4000 m. Off the coast of El Salvador lies the Middle America Trench, an active subduction boundary and seismic zone between the Cocos and Caribbean plates (Dewey et al. 2004). As a consequence of plate subduction, El Salvador is bisected by the volcanic front, a linear belt of active volcanoes, and accompanying seismic zone where earthquakes are common (White et al. 2004).

Freshwater habitats

Freshwater habitats in this ecoregion include an interesting combination of mountain streams, canyon creeks, coastal lagoons, and crater lakes. Mangroves and tidal flats dominate estuarine shorelines, with salt marshes occurring inland in hypersaline sediments.

Mexico is home to numerous minor coastal basins. Of these, Rìo Tehuantepec is the largest, and includes the coastal lagoon complex of Mar Muerto, Superior, and Inferior. Among the most important watersheds in El Salvador is the Lempa River. It originates in Guatemala, flows a short distance through southwestern Honduras, and then travels through much of the central plateau in El Salvador before it cuts through the southern volcanic range to empty into the Pacific. Other rivers are generally short and drain the Pacific lowlands or flow from the highlands to the Pacific. Numerous lakes of volcanic origin are found in the interior highlands of Guatemala and El Salvador.

Terrestrial habitats

Chiapas-Fonseca covers four different habitat types, including mangroves, tropical and subtropical dry broadleaf forests, tropical and subtropical moist broadleaf forests, and tropical and subtropical coniferous forests. Mangroves and tidal flats line most of the coastline with species of Rhizophora mangle, R. harrisonii, and R. racemosa (Chapman 1992). 

The Central American dry forest ecoregion is the larger and southernmost of the dry forest terrestrial ecoregions in this freshwater system. Ranging between 0 and 800 m, it is characterized by an upper story dominated by species of the Leguminosae superfamily, and a lower story that usually includes more evergreen species and members of the Rubiaceae family. The ecoregion is noted for its elements from both North and South America. It also contains a large percentage of endemic flora and fauna, with at least 50 plant species endemic to the region (Bullock 1995).

Forming a transition between the low elevation dry forests and high elevation pine-oak forests is a strip of moist forests that flank the western Sierra Madre de Chiapas in the northern part of the ecoregion. These are replaced by pine-oak forests at higher elevations. The largest of these ecoregions is the Central American pine-oak forests. This terrestrial ecoregion, which extends across the eastern side of the Chiapas-Fonseca ecoregion, supports a rich assortment of conifer species, including pines (Pinus spp.) and oaks (Quercus spp.). Pine-oak forests are found at altitudinal ranges that vary from 600 to 1,800 m above sea level (Harcourt & Sayer 1996). Unfortunately the pine-oak forests in El Salvador have almost entirely been cleared (WWF 2001).

Description of endemic fishes

The ecoregion contains a large number of endemic species compared to its neighbors to the north and south [170, 204]. Some of the endemics include the blackthroat cichlid (Amphilophus macracanthus), Pacific foureyed fish (Anableps dowei), Soconusco gambusia (Brachyrhaphis hartwegi), Riverine stargazer (Dactyloscopus amnis), Poecilia marcellinoi, Tonala catfish (Rhamdia parryi), Amatitlan cichlid (Vieja guttulata), and Oaxaca cichlid (V. zonata).

Other noteworthy fishes

Lake Guija, El Salvador’s largest natural lake, and Laguna de Metapan harbor at least two globally threatened fish species, Cichlasoma guija and C. trimaculatu. (WorldBank 2005).

Justification for delineation

The Mexican portion of this ecoregion was based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government. For the rest of the ecoregion, fish provinces from Bussing (1976) were revised and subdivided on the basis of the application of the similarity index to subbasin fish presence/absence data. Endemic species as well as the northernmost limit of several taxa help distinguish this ecoregion.

Level of taxonomic exploration

Fairly good