Location and General Description
Usumacinta mangrove ecoregion is located in the state of Tabasco, Mexico. The delta of the rivers Usumacinta and Grijalva delineates the mangrove habitat as well as other hydrophyllic communities. Soils are deep, very acidic, and rich in organic matter; this, together with their clay-like nature, makes them among the most productive soils in the country (López-Hernández & Pérez-López 1993). The climate is warm-humid with abundant rains in summer, and this mangrove ecoregion is one of the wettest, with 1,600 mm annually, in the area. Due to its climatic and biologic characteristics, Usumacinta mangroves and the nearby floodlands are considered the most important wetlands of the country (SEMARNAP 1997). The area is situated in a vast plateau with occasional flood plain formations. The coastal plains form part of the Grijalva-Usumacinta fluvial system, which constitutes Mexico's biggest discharge of freshwater into the ocean (SEMARNAP 1997). Mangroves carry clay-mud sediments due to the influence of the Usumacinta-Grijalva current. Intrusions of salt water during the dry season allow mangroves to form up to 30 km inland.
The vegetation is established on top of the fluvial plain and on soils with very high organic matter content. Red mangrove (Rhizophora mangle), white mangrove (Laguncularia racemosa), and black mangrove (Avicennia germinans) are the key species in the community, and they are associated with Dalbergia brownii scrubs as well as with other hydrophyllic communities formed by Acoelloraphe wrightii or Sabal mexicana palm trees (Rzedowski 1988). As in most mangroves, herbaceous associations are not abundant in these communities because they are intolerant to permanent floods (Lot et al. 1993).
It has been estimated that the mangroves surrounding Laguna de Términos, of this ecoregion receive at least 33% of the population of migrant birds that follow the Mississippi route (SEMARNAP 1997), another fact that gives special importance to this place as a natural refuge. Mangroves are also recognized as good soil retainers (Rzedowski 1988), and this ecoregion is not exempt from this biologically important feature. The area contains 374 species of plants, 60 species of fish, 26 amphibians, 85 reptiles, 279 birds, and 134 mammals. Along with the aquatic vegetation that is present in Laguna de Términos, the area contains 1,468 species of aquatic and terrestrial organisms, of which 30 are endemic to Mexico. Moreover, Laguna de Términos holds nearly 90 endangered species. The diverse geomorphological features of Usumacinta mangroves allow the formation of a complex hydrological system of marshes, lagoons, and other water bodies that together share most of the aquatic species of the ecoregion. The area is highly important as a refuge for the manatee (Trichechus manatus), an endangered species.
Black hawk-eagle (Spizaetus tyrannus), masked duck (Oxyura dominica), king vulture (Sarcoramphus papa) and crane hawk (Geranospiza caerulescens) are all resident species that are considered rare according to the IUCN red list. Cacomistle (Bassariscus sumichrasti), Underwood's long-tongued bat (Hylonycteris underwoodi), Davis' round-eared bat (Tonatia evotis) and Mexican agouti (Dasyprocta mexicana) are mammals found in this mangrove ecoregion.
Mangroves have been gradually eliminated in this ecoregion, due to their importance as a source of food and timber for local villagers (López-Hernández & Pérez-López 1993). It is estimated that only 13.5% of the area encompassed by the mangroves and nearby habitats remain intact. The Usumacinta mangrove ecoregion forms part of the Biosphere Reserve of Pantanos de Centla, which was established in 1992, and were designated as a wetland of international importance under the RAMSAR convention in 1995 (Frazier 1999). Federal protection has begun, and a management plan for the area is currently being undertaken to prevent accelerated habitat loss, and to introduce the idea of sustainable natural resource use in such a rich and biologically diverse ecoregion; one of the most important wetlands in Mexico.
Types and Severity of Threats
Exploitation of local fisheries and of mangrove trees is the major threat to the habitat. This is the primary reason for high numbers of species in danger of extinction, in the state of Tabasco. Habitat fragmentation and destruction are bound to continue, and with them, a major loss of animal species of great importance. The area contains 19 species of threatened animals, as well as 5 that are considered rare species. Moreover, the mangroves and adjacent habitats are home to most of the individuals of storks (Jabiru mycteria) that survive in Mexico, and are the preferred breeding place of the endangered Morelet’s crocodile (Crocodylus moreletii).
Long-term threats to the region include overexploitation of resources, continuous industrial pollution of the waters due to human overpopulation, oil extraction, and the possible construction of building a hydroelectric plant that would impact a large part of the aquatic habitat. According to IUCN (Scott & Carbonell 1986), the Gulf Coast contains the largest area of wetlands in North America.
Justification of Ecoregion Delineation
Classification and linework for all mangrove ecoregions in Latin America and the Caribbean follow the results of a mangrove ecoregion workshop (1994) and subsequent report (Olson et al. 1996).
Ecoregional Workshop: A Conservation Assessment of Mangrove Ecoregions of Latin America and the Caribbean. 1994. Washington D.C., World Wildlife Fund.
Flores-Villela, O. & Gerez, P. 1988. Conservación en México: síntesis sobre vertebrados terrestres, vegetación y uso del suelo. Instituto Nacional de Investigaciones Sobre Recursos Bióticos. Conservación Internacional. 302 pp.
Frazier, S. ed. 1999. A directory of wetlands of international importance (designated under the RAMSAR convention). Compiled by Wetlands International. http://www.wetlands.agro.nl/ramsar.database.
INIREB. 1986. Plan de Manejo para la reserva de la biósfera "Los pantanos de Centla, Tabasco, México".
López-Hernández, E.S. & Pérez-López, C. 1993. Guia para la Interpretación de la Naturaleza en los Pantanos de Centla, Tabasco. Centro de Investigacion de Ciencias Biológicas, Unidad Sierra. Tabasco, México. 106 pp.
Lot, A., Novelo, A., & Ramírez-García, P. 1993. Diversidad de la flora acuática mexicana. In: Ramamoorthy, T.P., Bye, R., Lot, A., & Fa, J. (eds). Diversidad Biológica de México. Orígenes y Distribución. Instituto de Biología, UNAM. Pp. 563-578
Olson, D.M., E. Dinerstein, G. Cintrón, and P. Iolster. 1996. A conservation assessment
of mangrove ecosystems of Latin America and the Caribbean. Final report for The
Ford Foundation. World Wildlife Fund, Washington, D.C.
Rzedowski, J. 1988. Vegetación de México. Editorial Limusa, México. 431 pp.
Scott, D. A. & Carbonell, M. (Comp.). 1986. Inventario de Humedales de la Región Neotropical. IWRB Slimbridge & IUCN Cambridge. U.K. 714 pp.
SEMARNAP. 1997. Programa de Manejo del Area de Protección de Flora y Fauna Laguna de Términos. SEMARNAP, México. 167 pp.
Prepared by: Alejandra Valero
Reviewed by: In process