Location and General Description
This mangrove ecoregion is divisible into eastern and western parts, to either side of the Bahía de São Marcos, where the island of São Luis is located. The eastern part consists of extensive sand dunes interspersed with mangroves, which are restricted to river mouths and bays. The western part, which receives fined grained sediment deposited by the Amazon River, consists of hundreds of islands and mudflats. These are continuously colonized and stabilized by mangroves, which cover the coastal fringe and also penetrate inland along its numerous rivers, bays and estuaries (Rebelo-Mochel 1997). Because of flat topography and high tidal ranges, that average 4 m but are known to exceed 8 m in some locations, saline waters and mangroves can be found over 40 km inland. The climate is hot and humid, with a mean annual temperature of 26° C. Annual precipitation is also high, averaging 2,500 mm but reaching levels of over 4,000 mm. Because of high freshwater inputs from rainfall as well as from numerous rivers, mangrove vegetation is also found associated with palms and freshwater macrophytes (Kjerfve and Lacerda 1993). Towards the eastern side of the north coast of Brazil, mangroves are progressively less developed because of higher salinity and longer dry seasons.
The mangroves of the Maranhão ecoregion are one of the most important areas for shorebirds in South America - approximately 200,000 were found in censuses conducted in 1982 and 1986 or 50% of Brazil’s total population of shorebirds and 7% of South American shorebirds that have been verified. They are also an important feeding and reproductive area for herons (Ardeidae) and spoonbills (Ajaia ajaja) (Frazier 1999).
Rhizopora mangle is the most frequently occurring mangrove species and is found closest to the coast at heights of up to 25 m. Also particularly well developed along the north coast of Brazil is Avicennia germinans and A. schaueriana, which may be over 1 meter in diameter and reach heights of up to 45 meters. Other true mangrove species found in this region are R. racemosa, R. harrisonii, Laguncularia racemosa and Conocarpus erectus. Non-tree species associated with these mangroves are Spartina alterniflora that grows on the seaward fringe, and Hibiscus tiliaceus and the fern Acrostichum aureum, that are both found in the landward margins and dry saline areas within mangroves. Species found associated with these mangroves because of their location adjacent to tropical forests and because of high freshwater input include the tropical forest species, leguminosae vine (Dalbergia brownei), and Apocynaceae liana (Rhabdadenia biflora); freshwater macrophytes, Araceae Montrichardia arborescens, and Leguminosae Mora oleifera; and palm species, Euterpe oleracea and Orbygnia martiana (Kjerfve and Lacerda 1993).
Rare and endangered species include the birds scarlet ibis (Eudocimus ruber), and wattled jacana (Jacana jacana), the mammals tucuxi (Sotalia fluviatilis) and manatee Trichechus manatus, and several marine turtles, for whom it is a breeding area (Frazier 1999; Diegues et al 1995).
This ecoregion contains approximately 36% of the total Brazilian mangrove area, which is largely intact because of low population density and poor accessibility (Kjerfve and Lacerda 1993). Protected areas include the Bacanga State Park on São Luis Island, and the Lencóis Maranhenses National Park, which is considered a wetland of international importance under the RAMSAR convention, and is also a Western Hemisphere Shorebird Reserve Network Site. In addition there are three environmental protection areas, an extractive reserve and a state park. However, it is not clear what percentage of these consist of mangroves.
Types and Severity of Threats
Over exploitation of the resources available in the mangroves of this ecoregion is a major threat. These mangroves however, are important to the subsistence economy of numerous artisanal fishermen, particularly for their abundance of crabs. In addition to fishing, mangroves are used as timber for construction of boats and houses, and their barks as a source of tannin used to dye ship sails. They are also used for firewood and charcoal. In some areas, mangroves have been converted to rice cultivation or to residential and industrial development, which has resulted in the extraction of forest products for industrial use, and the discharge of domestic and industrial wastes. The mangroves of Tutóia alone, which are near the Piauí border, were found to support 1,800 artisanal fisherman who caught 1,162 tons of shrimp in 1977. Other concerns are commercial fishing primarily for shrimp, and gold mining which has led to mercury contamination. (Kjerfve and Lacerda 1993; Rebelo-Mochel 1997; Ubiratan et al 1999).
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: Sylvia S. Tognetti and Christine Burdette
Reviewed by: In process