Location and General Description
The Marismas Nacionales/San Blas mangroves ecoregion is located in the physiographic province of the northwest mountains and plateaus of Mexico (Ferrusquía-Villafranca 1993). It is situated on a vast plateau with various beaches that isolate waters and shape them into many barrier coastal islands with lagoons, some of which are ephemeral, (Contreras 1988) and at the mouths of many rivers including the Rio San Pedro. The coast of Nayarit contains 705 km2 of mangrove associations, representing 22% of the area occupied by mangroves in Mexico (Bojórquez et al. 1997). Although the mangroves grow on flat terrain, the seven rivers that feed the mangroves descend from mountains, which belong to the physiographic province of the Sierra Madre Occidental. The climate varies from temperate-dry to subhumid in the summer, when the region receives most of its rainfall (more than 1000 mm/year).
Red (Rhizophora mangle), black (Avicennia germinans), button (Conocarpus erectus) and white mangrove trees (Laguncularia racemosa) are occur in this ecoregion. In the northern part of the ecoregion near Teacapán the black mangrove is dominant; however, in the southern part nearer Agua Brava the white mangrove dominates according to Seeliger (2001). Herbaceous vegetation is rare (Lot et al. 1993), but other species that can be found in association with mangrove trees are: ciruelillo (Phyllanthus elsiae), zapotón (Pachira acuatica), and anona (Anona glabra).
The mangroves of Sinaloa and Nayarit represent the largest extent of mangroves in the Mexican Pacific (Bojórquez et al. 1997). They are considered crucial habitat for many species of migratory birds, and house many species of high ecological and commercial value (Ibid.). They support enormous quantities of invertebrates on which many species of aquatic birds and other terrestrial vertebrates feed; thus, they are natural promoters of biodiversity in aquatic environments. Odum & de la Cruz (1967) stated that 2/3 of the fish populations worldwide depend on mangrove ecosystems during at least one or more stages of their lives and these ecosystems have often been referred to as nurseries for the marine world.
Mangroves form a natural refuge for many species of invertebrates and vertebrates; it is estimated that each hectare of mangrove removed will lead to a loss of 750 kg of commercially important species (Bojórquez 1997). There are endemic reptiles and amphibians which including a important population of Morelet’s crocodile (Crocodylus moreletti)and crocodiles (Crocodylus acutus) in the freshwater marshes associated with tropical palm forest (Orbygnia cocyule) (Olson et al 1996). Also present in this ecoregion are reptiles such as green iguanas (iguana iguana), Mexican beaded lizards (Heloderma horridum), yellow bellied slider (Trachemys scripta) and mammals including pumas (Puma concolor), ocelots (Leopardus pardalis), jaguars (Panthera onca), southern pygmy mouse (Baiomys musculus), Saussure's shrew (Sorex saussurei) and many bat species such as fruit eating (Durmanura phaeotis, D. aztecus, D. toltecus) and myotis (Myotis volans, M. furtidens). Four species of endangered sea turtle use the coast of Nayarit as a nesting site including leatherback turtles (Dermochelys coriacea), olive Ridley turtles (Lepidochelys olivacea), hawksbill turtles (Eretmochelys imbricata) and green turtles (Chelonia mydas).
There are more than 252 species of birds, 40% of which are migratory, including 12 migratory ducks (Frazier 1999) and approximately 36 endemic birds including the bumblebee hummingbird, (Atthis heloisa) and the Mexican woodnymph (Thalurania ridgwayi) (CONABIO 1999). Bojórquez (1997) considers the mangroves of Nayarit and Sinaloa among the areas of highest concentration of migratory birds. This ecoregion also serves as wintering habitat and as refuge from surrounding habitats during harsh times for many species, especially birds (Olson 1996) elevating the conservation value of this habitat. Some of the many representative avifauna are black-bellied tree duck (Dendrocygna autumnalis), great blue heron (Ardea herodias), roseate spoonbill (Ajaia ajaja), snowy egret (Egretta thula), sanderling (Calidris alba), American kestrel (Falco sparverius), blue-winged teal (Anas discors), northern jacana (Jacana spinosa), elegant trogan (Trogan ambiguus), summer tanager (Piranga rubra), white-tailed hawk (Buteo albicaudatus), merlin (Falco columbarius), plain-capped starthroat (Heliomaster constantii), painted bunting (Passerina ciris) and wood stork (Mycteria americana) (CONABIO 1999).
There is not adequate information on how well preserved the region is or how intact the habitat remains. Mangroves have been gradually eliminated due to their potential as a source of wood for human use.
Types and Severity of Threats
Water pollution due to industrial and agricultural activities threatens the biota that depends on the resources provided by mangroves and other water bodies. Logging is extensive in the area, and could eventually lead to loss of the habitat for all these species. Artificial drainage and construction of dams for use as cultivable lands and highways alter hydrological regimes, putting these actions among the major threats facing mangroves. Drainage also leads to a loss of the nutrients stored by mangroves, which destabilizes the communities that depend on them. The introduction of exotic species such as the common carp (Cyprinus carpio), and the blue tilapia (Oreochromis aureus) (CONABIO 1998) also alters the original relationships among the native members of these communities.
The destruction of mangroves has had severe consequences for the fish industry of countries like Ecuador, Malaysia, Philippines, India, and Japan (Bojórquez et al. 1997); if the deforestation of Mexican mangroves persists, the same could happen to Mexico’s fisheries. Long-term threats to the region are overexploitation of resources and continuous industrial pollution of the waters due to human overpopulation. The site was designated as a wetland of international importance under the RAMSAR convention in 1995 because it contains 51 endemic vertebrates and at least 60 endangered ones. Important solutions include managing the mangroves, as well as regulating the illegal extraction of wildlife and water pollution by humans and industrial settlements.
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).
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Prepared by: Alejandra Valero and Christine Burdette
Reviewed by: In process