Marismas Nacionales-San Blas mangroves
The Marismas Nacionales-San Blas mangroves ecoregion contains the most extensive block of mangrove ecosystem along the Pacific coastal zone of Mexico, comprising around 2000 square kilometres. All mangroves synthesize organic matter and filter nutrients, thus being ecologically critical for the maintenance of high productivity in tropical coastal zones. In fact, the mangroves in Nayarit are among the most productive systems of northwest Mexico. These mangroves and their associated wetlands also serve as one of the most important winter habitat for birds in the Pacific coastal zone, by serving about eighty percent of the Pacific migratory shore bird populations.
The Marismas Nacionales-San Blas mangroves can be viewed as a subset of the somewhat larger Northern Mesoamerican Pacific mangroves ecoregion; this larger ecoregion also includes elements of the Pacific coast of Baja California as well as elements of the Pacific coast of southern Mexico. The Marismas Nacionales-San Blas mangroves, however, are strictly confined to coastal zones of Nayarit and Sinaloa, Mexico.
Location and general depiction
The Marismas Nacionales/San Blas mangroves ecoregion is located in the physiographic province of the northwest mountains and plateaus of Mexico. It is situated on a vast plateau, with various beach landforms that isolate waters and shape them into many barrier coastal islands with lagoons, some of which are ephemeral, and at the mouths of many rivers including the Rio San Pedro. The coast of Nayarit contains 705 square kilometres of mangrove associations, representing about twenty-two percent of the area occupied by mangroves in Mexico. The coasts of Sinaloa harbour almost 1300 square kilometres of mangrove forest. Although the mangroves grow on flat terrain, the rivers that feed the mangroves descend from mountains, many of which belong to the physiographic province of the Sierra Madre Occidental. The climate varies from temperate-dry to sub-humid in the summer, when the region receives most of its rainfall (more than 1000 millimetres /year).
Red Mangrove (Rhizophora mangle), Black Mangrove (Avicennia germinans), Buttonwood (Conocarpus erectus) and White Mangrove trees (Laguncularia racemosa) are dominant trees in this ecoregion. In the northern part of the ecoregion near Teacapán the Black Mangrove tree is dominant; however, in the southern part nearer Agua Brava, White Mangrove is more prevalent. Herbaceous vegetation is rare, but other species that can be found in association with mangrove trees are: Ciruelillo (Phyllanthus elsiae), Guiana-chestnut (Pachira aquatica), and Pond Apple (Annona glabra).
The mangroves of Sinaloa and Nayarit represent the largest extent of mangroves in the Mexican Pacific. They are considered crucial habitat for many species of migratory birds, and harbour many species of high ecological and commercial value. They support enormous quantities of invertebrates, upon which many species of aquatic birds and other terrestrial vertebrates feed; thus, they are also natural promoters of biodiversity in aquatic environments. Odum & de la Cruz stated that two thirds of the fish populations worldwide depend on mangrove ecosystems during at least one or more life-stages, and these ecosystems have often been referred to as nurseries of 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 approximately 750 kilograms of biomass involving commercially important species .
There are are a number of reptiles and amphibians which including a important population of Morelet's Crocodile (Crocodylus moreletii) and American Crocodile (Crocodylus acutus) in the freshwater marshes associated with tropical Cohune Palm (Attalea cohune) forest. Also present in this ecoregion are reptiles such as the Green Iguana (Iguana iguana), Mexican Beaded Lizard (Heloderma horridum) and Yellow Bellied Slider (Trachemys scripta).
Four species of endangered sea turtle use the coast of Nayarit for nesting sites including Leatherback Turtle (Dermochelys coriacea), Olive Ridley Turtle (Lepidochelys olivacea), Hawksbill Turtle (Eretmochelys imbricata) and Green Turtle (Chelonia mydas).
A number of mammals are found in the ecoregion, including the Puma (Puma concolor), Ocelot (Leopardus pardalis), Jaguar (Panthera onca), Southern Pygmy Mouse (Baiomys musculus), Saussure's Shrew (Sorex saussurei). In addition many bat taxa are found in the ecoregion, including fruit eating species such as the Pygmy Fruit-eating Bat (Artibeus phaeotis); Aztec Fruit-eating Bat (Artibeus aztecus) and Toltec Fruit-eating Bat (Artibeus toltecus); there are also bat representatives from the genus myotis, such as the Long-legged Myotis (Myotis volans) and the Cinnamon Myotis (M. fortidens).
There are more than 252 species of birds, 40 percent of which are migratory, including 12 migratory ducks and approximately 36 endemic birds, including the Bumblebee Hummingbird, (Atthis heloisa) and the Mexican Woodnymph (Thalurania ridgwayi). Bojórquez 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 climatic conditions for many species, especially birds; this sheltering effect further elevates the conservation value of this habitat.
Some of the many representative avifauna are Black-bellied Whistling 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), Mexican Jacana (Jacana spinosa), Elegant Trogan (Trogan elegans), 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).
There is inadequate information on how well preserved the region is or how intact the habitat remains. Mangroves in the ecoregion have been gradually eliminated by indigenous peoples to their value as a source of wood for human use.
The conservation status of this mangrove ecoregion is considered Critically endangered, due to the variety and intensity of threats, and to the extent of present degradation. 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, water diversions 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) 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; 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, of which at least 60 are endangered. 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 and subsequent reportage. The ecoregion is denoted by the unit NT1420 under the World Wildlife Fund nomenclature.
The Marismas Nacionales-San Blas mangroves can be viewed as a subset of the larger Northern Mesoamerican Pacific mangroves ecoregion, which larger ecoregion includes elements of the Pacific coast of Baja California as well as certain coastal zone elements of the Pacific coast of southern Mexico. The Marismas Nacionales-San Blas mangroves, however, are strictly confined to coastal zones of Nayarit and Sinaloa, Mexico.
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