Boundaries

This coastal ecoregion encompasses the Río Papaloapan basin, which covers most of central Veracruz, two disjunct portions of eastern Puebla, and part of northern Oaxaca.

Topography

The headwaters of the Papaloapan rise in the Sierra Madre Oriental in the western part of the ecoregion, and then drain towards the Gulf of Mexico. Elevations in the ecoregion range from sea level to over 3000 m asl. Sierra Madre de Oaxaca lies in the southwest and the Eje Volcánico lies at the northern border.

Freshwater habitats

Freshwater habitats include headwaters, springs, creeks, lakes, lagoons, falls, rapids, and pools.

In the northeastern part of the ecoregion is Laguna de Catemaco, a volcanic crater lake 335 m above sea level. A number of small streams flow down the interior face of the crater into the lake, which has an outlet to the northeast into a river known locally as the Río Grande. Twelve kilometers downstream of the outflow, a 45-meter high waterfall, the Salto de Eyiplanta, effectively isolates the lake from the lower reaches of the Río Papaloapan system. The lake is extremely turbid due to suspended particles of basaltic dust.

Terrestrial habitats

The ecoregion contains a variety of terrestrial ecoregions, including moist forests, dry forests, and mangroves along the coast and pine-oak forests, dry forests, and matorral at higher elevations.

Description of endemic fishes

The Papaloapan ecoregion is characterized by relatively high endemism within its ichthyofauna. Around 28 percent of the native fish species are endemic to this region. Endemics include the graceful priapella (Priapella bonita), Olmec priapella (P. olmecae), blindwhiskered catfish (Rhamdia reddelli), and species of Atherinella and Xiphophorus. Also within this ecoregion is Laguna de Catemaco, a remarkable lake with endemic fish such as the Catemaco characin (Bramocharax caballeroi).

Justification for delineation

Ecoregion delineations were based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government. Although the Papaloapan, Coatzacoalcos, and Usumacinta rivers share genera or lower level species complexes, there are endemic and distinctive species for each basin, like the series of Priapella, Atherinella, Theraps, and Thorichthys. This justified the distinction of each basin as a separate ecoregion.

Level of taxonomic exploration

Poor along the western mountainous headwaters and also around coastal lagoons, but regular within the middle ranges.