Location and General Description
This extensive mangrove ecoregion follows along the Pacific Coasts of Columbia and Ecuador encompassing stands of mangrove ecosystems along the way. Some of the larger stands are found in Tribugo Bay at the northern extent of the ecoregion then working south through the mouth of the San Juan River, Naya River, Guapi River, Mira River, Esmeraldas River finally ending at just south of the Mompiche Bay.
The ecoregion generally has two large mangrove zones divided by Cabo Corrientes in Colombia. Toward the north there is a predominance of the narrow continental platform, rugged coastal topography with elevations rising up to 1500 m, strong low-intensity coastal current upwellings and high annual precipitation, between 4000 and 8000 mm. The mouths of numerous small and clear water rivers empty into this northern part of the ecoregion throughout the year affecting vegetation structure. Toward the southern part of this ecoregion lies the sedimentary basin and the great coastal plain, with the dominant broad continental platform, flat coastal topography, no coastal current upwellings and lower annual precipitation of between 1000-4000 mm. The mouths of some large rivers including the Mataje, Mira, Patía, Sanquianga and Guapi River Deltas and about 25 minor rivers produce higher influx of freshwater but it is frequently much more turbid than the waters of the north (Prhal et al. 1990; Alvarez-León 1993). The lithology of the terrain consists primarily of lutites, sandstones, conglomerates and a lower proportion of limestones (Correa and González 1989).
The environmental parameters together with the microtopography lead to different types of mangrove forests: bar, inverted, coastal, dwarf, border and small island. Five families of vegetation with about 10 species have been identified for the mangrove ecosystems. These include Rhizophoraceae with Rhizophora harrisoni, R. Mangle, R. racemosa and R. samoensis; Caesalpinaceae with Mora oleifera; Avicenniaceae with Avicennia germinans and A. tonduzzi; Cambretaceae with Conmocarpus erecta, Laguncularia racemosa and Pellicieraceae with Pelliziera rhizophorae. Mangrove forests cannot be considered as an ecosystem separate from their surroundings due to the extensive areas they cover which are influenced by surface waters, sea water column and estuaries, soil and surrounding landscape vegetation (Prahl et al. 1990). The most significant, large groups of organisms associated with the ecoregion are: microorganisms (bacteria and fungi), algae communities (chlorophytes, rhodophytes and phaeophytes); invertebrates, polyquetae, molluscs (gastropods and bivalves); arthropods (amphipods, decapods and cirripedes); sinpunculids and priapulids; bryozoans; vertebrates; fish; reptiles (iguanas, "basiliscos"); birds and mammals (tigrillo, nutria, "venado", "guagua", "tatabro") (Cantera 1994). The mangrove forest is generally a transition zone dominated by the nato mangrove (Mora oleifera) and the naidisales (Euterpes spp.). The ferns Acrostichum aureum or "Ranconcha" that form the true fresh water marshes appear later, as succession progresses. The communities that occupy this zone are generally known by the name guandales or cuangarales consisting of forests with cuángare (Virola spp.), "Sajo" (Compnosperma panamensis), "Sande" (Brosimun utile) and others. Communities of palms such as Mauritiella pacifica, Manicaria saccata, and Euterpe cuatrecasa also appear in these swamps (Prahl et al. 1990).
The mangrove forest reflects the origins and reproductive potential of two-thirds of the species of fish in the world. Its dual status as a nursery and food source make high fish productivity (Castaño-Uribe 1989). Also notable are its action in the accretion or formation of soils, its role as a protective barrier defending the coast line against the permanent action of the tides and even against some natural phenomena like tsunamis and sea swells (Guevara-Mancera et al. 1998). The species Mora oleifera is a species endemic to the Pacific coast in the Americas; it is found from Parrita, Costa Rica to Esmeraldas, Ecuador (Gentry 1982; Jiménez 1994).
Mangrove species are characterized by adaptations for terrain that is unstable, anaerobic and inundated with saline influence (stilt or plank roots with lenticels and pneumatophores in some species). Mangroves also have reproductive strategies for coastal areas such as the high rate of reproduction and viviparous seedlings designed to float for great distances. Species of Rhizophora have a high plant reproduction rate allowing them to colonize very unstable terrain by opening their supporting surface. Samples with as many as five different stems interconnected by stilt roots are seen. In some species of Rhizophora, the cut trunks easily sprout again (Sánchez-Páez 1994). The ecological factors limiting the mangrove forests are high average temperature with little variation, abundant rains throughout the year, intermittent flooding caused by the tides and producing a mix of salt water and river water at river mouths and deltas. The mangrove forest floods periodically at high tide and is dry with the same frequency at low tide (Cuatrecasas 1958a) creating a source of natural selection for the vegetation capable of living with these conditions such as mangrove species and some palm species.
The development of the vegetation typical of mangrove ecosystems reflects in a general way the balance and interaction of all the factors that favor its development including temperature, wind and subsiquent evaporation rates, type of soil, salinity and fresh water sources and drainage and aeration of soils. For this reason, any one of them produces beneficial effects or destructive and limiting effects if they are much outside the range of resource tolerance of the species. Due to their open system characteristics, mangrove forests are able to release from 8 to 15 tons/hectare/year of organic matter, providing raw material to maintain a broad range of associated organisms, given the direct relationship with the marine and land system, necessarily favoring balance in the trophic chain (Guevara-Mancera et al., 1998).
Of the species associated with the mangrove ecosystem, the piangua hembra (Anadara tuberculosa) is the basis for exclusively small-scale fishing developed primarily by the communities located in the south-central part of the ecoregion and currently over-exploited (Borda and Portilla, 1999).
On the continent, Colombia has two Natural National Parks (Sanquianga and Ensenada de Utría) that based on their status as protected areas promote mangrove development and positively reduce the effects of human action on the ecosystem. In addition, positive expectations have been created with the implementation of Civil Society Natural Reserves. Three reserves have been established in northern Colombia and efforts to increase this number are ongoing.
Types and Severity of Threats
These species have traditionally been used for construction, firewood, poles, coal, piles, pulp, to obtain tannin, and for fishing gear, cattle pens, etc. (Sanchez-Páez et al., 1997). Definitive losses or reduction of the mangrove forest are due to man-made and natural causes. As a group the human activities that in one way or another have played a part in the loss of the forest would include the construction of infrastructure for expanding towns, airfields, aquiculture pools, cutting and utilization of trees in unsustainable ways, exploitation of fishing resources associated with the mangrove (piangua), cutting of trees to change soil use and establishment of coconut crops. Natural effects reduce the mangrove forest through fluviomarine erosional processes, geomorphological processes and desalination of mangrove soils, allowing the invasion of non-halo-helophytic species (Zambrano-Escamilla and Rubiano-Rubiano, 1996).
Other factors have also played a part in recent decades, leading to the death of mangrove forests, and are directly related to the contamination of water with domestic and industrial waste, particularly the spilling of hydrocarbons (Guevara-Mancera et al., 1998).
The most numerous habitat block is a continuous strip from the Mataje river to Chanzará bay near Guapi; it is interrupted only to the north of Ensenada de Tumaco (Zambrano-Escamilla and Rubiano-Rubiano, 1996).
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: Carlos Borda
Reviewed by: Emilio Constantino