Rio Negro-Rio San Sun mangroves
Northern Atlantic coast, Costa Rica Photograph by Pam Cubberly
Rio Negro-Rio San Sun mangroves consist of a disjunctive coastal ecoregion in parts ofCosta Rica, extending to the north slightly into Nicaragua and south marginally into Panama. Mangroves are sparse in this ecoregion, and are chiefly found in estuarine lagoons and small patches at river mouths growing in association with certain freshwater palm species such as the Yolillo Palm (Raphia taedigera), which taxon has some saline soil tolerance, and is deemed a basic element of the mangrove forest here. These mangrove communities are also part of a mosaic of several habitats that include mixed rainforest, wooded swamps, coastal wetlands, estuarine lagoons, sand backshores and beaches, sea-grasses, and coral reefs.
This coastal area generally consists of low alluvial floodplain (sea level to twenty metres above sea level), intermixed within a network of black-water canals and creeks. In between are intertidal zones and backshores that are important nesting areas for endangered sea turtle species, that feed in the seagrass beds and visit mangrove habitats. This mangrove ecoregion is highly threatened by the human population explosion of the region and associated pressures on coastal development.
Location and general depiction
This ecoregion is situated along the ocean coastline just penetrating Nicaragua then extending southward to the border of Costa Rica and Panama (Ecoregions of Panama). The paucity of mangroves here is a result of the robust influx of freshwater to the coastline ocean zone of this ecoregion. Among the highest rates of rainfall in the world, this ecoregion receives over six metres (m) a year at the Nicaragua/ Costa Rica national border. Peak rainfall occurs in the warmest months, usually between May and September. A relatively dry season occurs from January to April, which months coincides with stronger tradewinds. Tides are semi-diurnal and have a range of less than one half metre. The sparseness of mangrove patches explains why little information is available for Atlantic coast mangroves in this ecoregion, and few publications have emerged that directly reference mangroves in this region.
The area is disturbed at least once in a century by hurricanes, which may result in a die-off of all mangroves, as occurred in the year 1988 as an outcome of Hurricane Joan, although the mangroves continue to regenerate. This weather induced periodicity keeps the mangroves relatively young and small in stature, and explains why the mangrove forests in this ecoregion tend to be found in even-age stands
Biodiversity features
The area of Costa Rica near the [[Nicaragua]n] border is considered to be the most species-rich in Costa Rica. Although not restricted to mangroves, incomplete census studies of wildlife conducted at a local biological station report 120 species of mammals, over 300 avian species and more than 100 species of reptiles and amphibians have been documented.
Of the sixteen species of endangered mammals known in Costa Rica, thirteen were found in this survey. Six of the seven nationally endangered reptiles occur in the ecoregion. Threatened species found in the region such as the American Crocodile (Crocodylus acutus), Baird's Tapir (Tapirus bairdii), Green Sea Turtles (Chelonia mydas), Dermochelys coriacea, and the Manatee (Trichecus manatus).
Reptiles
Reptiles include the Basilisk Lizard (Basiliscus basiliscus), Caiman (Caiman crocodilus), Green Sea Turtle (Chelonia mydas), Leatherback Turtle (Dermochelys coriacea) and Green Iguana (Iguana iguana). The beaches along the coast within this ecoregion near Tortuguero are some of the most important for nesting green turtles. The offshore seagrass beds, which are among the most extensive in the world, are a source of food and refuge for the endangered Green Sea Turtle (Chelonia mydas).
Amphibians
Several species of frogs of the family Dendrobatidae are found in this mangrove ecoregion as well other anuran species and some endemic salamander taxa.
Flora
Mangroves play an important role in trapping sediments from land that are detrimental to the development of both coral reefs and sea grasses that are associated with them. Mangrove species including Rhizopora mangle, Avicennia germinans, Laguncularia racemosa, Conocarpus erecta and R. harrisonii grow alone the salinity gradient in appropriate areas. Uncommon occurrences of Pelliciera rhizophorae and other plant species associated with mangroves include Leather ferns Acrostichum spp., which also invade cut-over mangrove stands and provide some protection against erosion. In this particular ecoregion, the mangroves are associated with the indicator species, freshwater palm, Raphia taedigera. Other mangrove associated species are Guiana-chestnut ( Pachira aquatica) and Dragonsblood Tree (Pterocarpus officinalis).
Mammals
Mammal species found in this highly diverse ecoregion include: Lowland Paca (Agouti paca), primates such as Mantled Howler Monkey (Alouatta palliata), Geoffrey's Spider Monkey (Ateles geoffroyi), White-faced Capuchin (Cebus capucinus), Brown-throated Sloth (Bradypus variegatus), Silky Anteater (Cyclopes didactylus) and Nine-banded Armadillo (Dasypus novemcintus). Also found in this ecoregion are carnivores such as Ocelot (Leopardus pardalis), Central American Otter (Lutra annectens), Jaguar (Panthera onca), Northern Racooon (Procyoon lotor), and Crab-eating Racoon (P. cancrivorus).
Birdlife
The ecoregion is of great importance as a stopover for migratory birds and is a breeding area for a number of fish that are important to the subsistence economy of the ecoregion. Birds that visit mangroves during migration include Spotted Sandpiper (Actitis macularia), Red-lored Amazon (Amazona autumnalis), Snowy Cotinga (Carpodectes nitidus), Wilson's Plover (Charadrius wilsonia), Green Kingfisher (Chloroceryle americana), Lesser Nighthawk (Chordeiles acutipennis), Common Nighthawk (Chordeiles minor), Keel-billed Motmot (Electron carintum), and Osprey (Pandion haliaetus) among numerous other avian taxa.
Ecological status
There also appears to be an increased incidence of tropical storms and hurricanes. According to data for the Corn Islands which are immediately outside the boundaries of this ecoregion, suggest that tropical storms occur on an average of once a year and that hurricanes are expected once every fifty years. However, in 1996, three tropical storms and one hurricane occurred, and three hurricanes have struck the Corn Islands in the past eight years. Although it is not possible to unequivocally link these particular extreme events with climate change, an increase in their frequency is consistent with certain scenarios of climate change, in that tropical storms have a tendency to occur over warmer ocean waters.
The protected areas in this region, include the Indio Maíz biological reserve in Nicaragua and the Tortuguero National Park and the Humedal Caribe Noreste in Costa Rica, are part of a network of Caribbean sites linked by a Meso-American Biological Corridor intended to insure continuity of biogeographical links between North and South America. The Humedal Caribe Noreste is also considered a wetland of international importance under the RAMSAR convention.
Ecological threat profile
Deforestation in the upper watershed has resulted in drainage and sedimentation problems. Also associated with these problems are the acceptable management practices used on banana plantations. The redirection of surface water flow as a result of dam construction is changing the mangrove habitat by either adding or removing the natural amount of freshwater inflow to the ecoregion. A list of other threats includes land use changes as a result of unplanned settlements, illegal hunting, development of an international port, plans for another canal between the Caribbean Sea and the Pacific Ocean, gold mining on the [[Nicaragua]n] side of the border, sewage contamination from towns, runoff of agricultural chemicals, and erosion. For lack of a unified management plan, these threats appear to vary depending on the side of the border and are more acute in Costa Rica.
Justification of ecoregion delineation
Classification and linework for all mangrove ecoregions in Latin America and the Caribbean follow the results of the 1996 WWF mangrove ecoregion workshop and subsequent reportage.
Further reading
- B. Kjerfve and D.J. Macintosh. 1997. The impact of climatic change on mangrove ecosystems. B. Kjerfve, L.D. Lacerda, and E.H.S. Diop E.H.S., editors. Mangrove ecosystem studies in Latin America and Africa. UNESCO, Paris France.
- Ecoregional Workshop: A Conservation Assessment of Mangrove Ecoregions of Latin America and the Caribbean. 1994. Washington D.C., World Wildlife Fund.
- Olson, David M., Eric Dinerstein, Gilberto Cintrón and Pia Iolster. 1996. A Conservation Assessment of Latin America and the Caribbean: Report from WWF's Conservation Assessment of Mangrove Ecorsystems of Latin America and the Caribbean Workshop. WWF, Washington D.C.
- Roth, L.C. 1997. Implications of periodic hurricane disturbance for the sustainable management of caribbean mangroves. B. Kjerfve, L.D. Lacerda, and E.H.S. Diop, editors. Mangrove ecosystem studies in Latin America and Africa. UNESCO, Paris France.
- Ryan, J.D., L.J. Miller, Y. Zapata, O. Downs, and R. Chan. 1998. Great Corn Island, Nicaragua. B.Kjerfve, editor, Caribbean coral reef, seagrass and mangrove sites. UNESCO, Paris France.
- P.B. Tomlinson. 1994. The Botany of Mangroves. Cambridge University Press. Pages 166-168. ISBN: 052146675X
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