Location and General Description
The mangroves are situated on the coastal plains of the Pacific, in the states of Michoacán, Guerrero, and Oaxaca. They are commonly associated with coastal lagoons, growing on the edge of these. Mangroves surround approximately eight of the eleven lagoons that are included in the ecoregion. Rivers that flow from the mountains of the Sierra Madre del Sur feed the mangroves and lagoons. The soils are commonly derived from sedimentary rocks; clay and mud compose the great majority of sediments that are stored in lagoons, as does sand.
The climate is tropical subhumid in the south near Oaxaca, but is drier to the northwest in Michoacán; summer rains are generalized throughout the region, but precipitation levels vary with altitude. The dominant mangrove species are red (Rhizophora mangle), white (Laguncularia racemosa), black (Avicennia germinans) and button mangrove (Conocarpus erectus) trees (Seeliger 2001). The salinity of the water and the degree of flooding in the area determine individual species abundance (Rzedowsi 1988). R. mangle is the most resistant of the four trees, while A. germinans and C. erectus are rare if the floods are permanent and submerge the trees too deeply in the mud. Herbaceous vegetation is scarce (Lot et al.1993), but species like Lyngbya sp., Cheatomorpha sp., and Ruppia maritima can be found in association with the mangroves. Other lagoons also include associations of tule (Typha sp.), Cyperus sp., and fruit trees like coconut (Cocos nucifera). Aquatic plants including water lilies such as Eichornia sp. and Chara sp. are common in the shallow lagoons.
In the southern pacific mangroves are responsible for most of the primary productivity in coastal lagoons. They supply lagoons with large quantities of detritus, which is later used by fish and invertebrates as a source of food. Detritus formed by decomposition of mangrove tree leaves constitutes an energy supply for communities associated with mangroves.
In addition to their importance as a unique habitat, and the extraordinary display of animal species that inhabit them; mangroves are a natural refuge for diverse species of birds, because they harbor many aquatic organisms on which birds feed such as oysters, crabs, invertebrate larvae and other bottom of the food chain organisms. These abundant primary resources make this ecoregion an attractive place for wintering birds to escape the colder northern climates and also serves birds in the process of migrating as refueling, stop-over areas. Resident species are represented by a great diversity of birds including wedge-tailed shearwaters (Puffinus pacificus), red-footed boobies (Sula sula), neotropic cormorants (Phalacrocorax brasilianus), little blue herons (Egretta caerulea), tricolored herons (Egretta tricolor), green herons (Bulbulcus virescens), sharp-shinned hawks (Accipiter striatus), Cooper's hawks (Accipiter cooperii), great black-hawks (Buteogallus urubitinga), zone-tailed hawks (Buteo albonotatus), laughing gulls (Larus atricilla), green-fronted hummingbirds (Amazilia viridifrons), Pacific-slope flycatchers (Empidonax difficilis) and many others (CONABIO2 1998). Winter resident birds also include many species such as American white pelicans (Pelecanus erythrorhynchos), American bitterns (Botaurus lentiginosus), ring-necked ducks (Aythya collaris), northern shovelers (Anas clypeata) and ruddy ducks (Oxyura jamaicensis) (CONABIO2 1998).
Other forms of wildlife in this ecoregion include both mammals and reptiles of many types however larger mammals do not live all the time in this ecoregion they wander using it as part of their range. A few of the mammal species that enter this ecoregion are: nine-banded armadillo (Daypus novemcinctus), white-tailed deer (Odocoileus virgianus), coyote (Canis latrans), tapir (Tapirus bairdii), jaguar (Panthera onca), sac-winged bat (Saccipteryx bilineata), northern tamandua (Tamandua mexicana) and hog-nosed skunk (Coneplatus mesoleucus) ( CONABIO 2000). Reptiles include species of iguanas (Ctenosaura spp.), skinks (Scincella spp.), lizards (Cnemidophorus spp.) and even subspecies of the venomous Brazilian rattlesnake (Crotalus durissus) and the endangered Morelet’s crocodile (Crocodylus morelitii) (CONABIO 2000).
There is not information on how well preserved this ecoregion is or how intact its habitat remains. Only one protected area is dedicated to the preservation of mangrove habitat, in Oaxaca. However, agriculture and cattle farming still threaten the habitat in Oaxaca as well as in Guerrero and Michoacán.
Types and Severity of Threats
Illegal hunting of wildlife threatens the biodiversity of the South Pacific coast mangroves. Native villagers have extensively hunted many species of aquatic birds (SEMARNAP 1999). Logging both commercially and locally for fuelwood is extensive in the region, which leads to loss of the mangrove associations and instability of the communities they support (Olson et al. 1996). Water pollution severely affects the plant and animal populations that inhabit lagoons and mangrove communities (CONABIO 1998). The introduction of exotic species such as blue tilapia (Oreochromis aureus) alters the ecological relationships among native organisms in the mangroves, and the extraction of wildlife could lead to progressive loss of biodiversity. All of these threats are accelerated and compounded currently by the continual increase in tourism (Olson et al.1996). Development to meet the needs of tourists is occurring and thus waste is increasing elevating pollution levels and further disrupting the mangrove ecosystems.
Management of the mangrove communities throughout the South Pacific coast is needed; deforestation rates should be especially controlled to avoid the quick loss of mangroves. Special attention should also be placed on the regulation of pollutants that are thrown to the coastal ecosystems (estuaries, mouths of rivers, lagoons and mangroves), to avoid poisoning and death of important plant and animal species.
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).
Comision Nacional Para el Conocimiento y Uso de la Biodiversidad (CONABIO) habitat and landuse classification database derived from ground truthed remote sensing data Insitituto Nacional de Estastica, Geografia, e Informática (INEGI)
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SEMARNAP. 1999. Parque Nacional Lagunas de Chacahua. www.semarnap.gob.mx/naturaleza/regiones/chacahua
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Prepared by: Alejandra Valero and Christine Burdette
Reviewed by: In process