Mexican South Pacific Coast mangroves
The Mexican South Pacific Coast mangroves ecoregion extends along the coastal zone of southern Mexico on the Pacific versant. Mangrove tree roots provide shelter for a considerable variety of fish, invertebrates, and medium-sized vertebrates that use these crevices as protective refuges. Mangroves promote biodiversity by providing shelter and food to many organisms. The relationships that are established and maintained in mangrove communities are ecologically beneficial, such as the use of these ecosystems by mammal species when resources are scarce in other areas. Mangroves are natural stabilisers of lagoon shores which help to maintain the coastal landscape, upon which many other species depend. Mangroves are recognised as important mechanisms for soil retention, and also allow for the formation of soil because they consolidate deposited sediment with organic matter, which supports the terrestrial communities associated with mangroves.
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 sub-humid 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 Mangrove (Rhizophora mangle), White Mangrove (Laguncularia racemosa), Black Mangrove (Avicennia germinans) and Buttonwood (Conocarpus erectus) trees. The salinity of the water and the degree of flooding in the area determine individual species abundance. R. mangle is the most resistant of the four trees, while A. germinans and C. erectus are rare if the floods are permanent, and trees become too deeply submerged in mud. Herbaceous vegetation is scarce, but species such as 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 certain fruit trees such as the coconut (Cocos nucifera). Aquatic plants, including water lilies such as Eichornia sp. and Chara sp., are common in the shallow lagoons.
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 ecological 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 considerable diversity of bird taxa, including the Wedge-tailed Shearwater (Puffinus pacificus), Red-footed Booby (Sula sula), Neotropic Cormorant (Phalacrocorax brasilianus), Little Blue Heron (Egretta caerulea), Tricolored Heron (Egretta tricolor), Green Heron (Butorides virescens), Sharp-Shinned Hawk (Accipiter striatus), Cooper's Hawk (Accipiter cooperii), Great Black Hawk (Buteogallus urubitinga), Zone-tailed Hawk (Buteo albonotatus), Laughing Gull (Leucophaeus atricilla), Green-fronted Hummingbird (Amazilia viridifrons), Pacific-slope flycatchers (Empidonax difficilis) and many other avian taxa. Winter resident birds also include many species such as the American White Pelican (Pelecanus erythrorhynchos), American Bittern (Botaurus lentiginosus), Ring-necked Duck (Aythya collaris), Northern Shoveler (Anas clypeata) and Ruddy Duck (Oxyura jamaicensis).
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), Greater Sac-winged Bat (Saccopteryx bilineata), northern tamandua (Tamandua mexicana) and hog-nosed skunk (Coneplatus mesoleucus). 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 moreletii).
There is not information on how well preserved this ecoregion is or the extent to which its habitat remains intact. Only a single protected area is dedicated to the preservation of mangrove habitat, in Oaxaca. Moreover, agriculture and cattle farming continue to threaten the natural habitat in Oaxaca as well as in the Mexican states of 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. Logging, both commercially and locally for fuelwood, is also widespread in the region, which deforestation leads to loss of the mangrove associations and instability of the communities they support. Water pollution severely affects the plant and animal populations that inhabit lagoons and mangrove communities. 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. 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 and subsequent report.
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