Freshwater Ecoregions of the World
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175: Yucatan

Author

Salvador Contreras Balderas (Universidad Autónoma de Nuevo León), Jennifer Hales

Reviewers

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Biodiversity
Species Richness
# of Endemic Species
Threats
Description

Major Habitat Type

Tropical and subtropical coastal rivers

Countries

Mexico

Boundaries

Restricted to the Yucatán Peninsula, this ecoregion encompasses northern Campeche, all of Yucatán, and northern Quintana Roo. Isla Cozumel is also part of this ecoregion.

Drainages flowing into

Gulf of Mexico and Caribbean Sea

Main rivers or other water bodies

The Yucatán includes many coastal streams that drain into the Gulf of Mexico and Caribbean, grottos, cenotes, and aquadas (sinkholes) in the interior of the peninsula. The ecoregion is also home to Laguna Chichancanab.

Topography

The Peninsula de Yucatán is a flat karst area with almost no hills. Elevations are less than 300 m, and soils are generally of calcareous origin. Laguna Chichancanab is nearly flat and surrounded by low hills.

Climate

The climate is predominantly tropical savanna. The ecoregion receives around 1000 mm rainfall annually, most of which falls between July and September.  The mean annual temperature is 26 ºC. Winter lows are around 16.5 ºC on average, while summer highs exceed 34 ºC.

Freshwater habitats

There is almost no permanent surface water in the Peninsula de Yucatán. However, subsurface waters connect to the surface via cenotes, aguadas, and calderas. Such water bodies may have fresh or brackish waters, and often are connected by subsurface rivers. The ecoregion is also distinguished by the presence of rias, streams that flow inland from the sea.

Laguna Chichancanab is an endorheic basin with lagoons that are highly saline due to evaporation. Few fish besides pupfishes are able to survive in this environment. There are no known drainages into the lake. Instead, it is mostly rain-fed, with the size of the lake and individual pools influenced by the amount of rain.

Terrestrial Habitats

Yucatán dry forests characterize most of the central and western side of the ecoregion, whereas Yucatán moist forests occur in the east and southern edge. Mangroves line the coast on both the Gulf of Mexico and Caribbean sides. Endemism is high in the dry forests, with roughly 75% endemism among cacti. Common cactus species in the dry forests include Cephalocereus gaumeri, Pterocereus gaumeri, and Lemaireocereus griseus.

Fish Fauna

From a freshwater perspective, the Yucatán is relatively unexplored biologically, and thus it is estimated that its true biodiversity is richer than the described species would suggest. Nonetheless, there is information on a number of native and endemic freshwater species. The most speciose families include Poeciilidae, Cyprinodontidae, and Cichlidae.

Description of endemic fishes

The ecoregion contains only a handful of strict endemics, including the giant killifish (Fundulus grandissimus), Yucatan killifish (F. persimilis), ocellated killifish (Floridichthys polyommus), and Cyprinodon suavium (Cyprinodontidae). The Mexican blind brotula (Typhliasina pearsei) is an uncommon endemic species found in caves and sinkholes.  Cyprinodon suavium is a pupfish endemic to Laguna Chichancanab. Among the near-endemic freshwater fish are five other pupfish that are also endemic to the Laguna Chichancanab in the Mexican state of Quintana Roo. These species are the blackfin pupfish (Cyprinodon beltrani), boxer pupfish (C. simus), Maya pupfish (C. maya), thicklip pupfish (C. labiosus), and largefin pupfish (C. verecundus).

Other noteworthy fishes

The ecoregion’s karst-derived subterranean habitats support a number of unusual species, such as the blind swamp eel (Ophisternon infernale). The Yucatan pupfish (Cyprinodon artifrons), ocellated killifish (Floridichthys polyommus), and Yucatan flagfish (Garmanella pulchra) reach their southern limit in Central America in the region.

Other noteworthy aquatic biotic elements

Two frogs, Triprion petasatus and Bolitoglossa yucatana, as well as the Creaser’s mud turtle, Kinosternon creaseri, are endemic to the Yucatán ecoregion. The ecoregion’s karst-derived subterranean habitats also support several subterranean amphipod crustaceans.

Evolutionary phenomena

The presence of cenotes, aguadas, and calderas give ample opportunity to develop cave forms (e.g., Mexican blind brotula and blind swamp eel), often grading to surface types.

In Laguna Chichancanab, the Cyprinodon fishes have radiated and formed a monophyletic species flock with distinct feeding habits (eg, one eats snails, another eats crustaceans, another insects, another is a bottom-feeder, etc.).

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. The Yucatán is noted for its unusual habitats, endemic species, and its impoverished, but peculiar, fauna that includes some cave-adapted species. Also, the ecoregion’s tropical and dry climate distinguishes it from adjacent ecoregions.

Level of taxonomic exploration

Most water bodies have not been explored; however, some recent discoveries have been important in redefining the significance of the peculiar habitats in the region. Less than half of the cenotes have been studied. Laguna Chichancanab is fairly well known, but access is difficult.

References

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