Moist Pacific Coast mangroves
The Moist Pacific Coast mangroves is an ecoregion along the Pacific coast of Costa Rica with a considerable number of embayments that provide shelter from wind and waves, thus favouring mangrove establishment. Tidal fluctuations also directly influence the mangrove ecosystem health in this zone. The Moist Pacific Coast mangroves ecoregion has a mean tidal amplitude of three and one half metres, but that may actually vary from two to six metres. Mangroves are more developed in this ecoregion than those further north, due to the higher rate of freshwater inflow that reduces salt accumulation in the mangroves by increasing evapotranspiration.
Location and general depiction
The moist Pacific Coast ecoregion runs along the coastline of Central America from near the town of Jaco, Costa Rica to the southwestern corner of the Peninsula de Azuero, Panama. This ecoregion encompasses the Gulfo Dulce, the Gulfo de Chiriquí, and the Gulfo de Montijo. This ecoregion's biological diversity results from its coverage of areas lying south of the Gulfo de Nicoya, which represent a transition zone of movement from dry to moist forest, with an abbreviated dry season (only January to March) and more precipitation in the wet season. Many of the streams and rivers, which help create this mangrove ecoregion, flow down from the Talamanca Mountain Range. Because of the resulting high mountain sediment loading, coral reefs are sparse along the Pacific coastal zone of Central America, and thus reef zones are chiefly found offshore near islands. In this region, coral reefs are associated with the mangroves at the Isla del Caño Biological Reserve, seventeen kilometres from the mainland coast near the Térraba-Sierpe Mangrove Reserve. The Térraba-Sierpe, found at the mouths of the Térraba and Sierpe Rivers, is considered a wetland of international importance.
In this ecoregion annual rainfall is higher than in the northern parts of Central America at greater than 2000 millimetres (mm), reaching 3647 mm at the southern end. The dry season is also shorter, averaging less than three months, resulting in better developed mangroves. Between May and December rainfall is influenced by the Intertropical Convergence Zone (ITCZ), an area of low atmospheric pressure where winds from the northern and southern hemispheres converge. These rains cover the ecoregion, and are considered the rainy season. The dry season occurs from January to April when the colder winds from the north push the ITCZ southward and bring about the upwelling of colder, nutrient-rich waters from below the surface. Small wetlands also function as reserves, slowly releasing water during the dry season. Fine sediment dominates most sites, although sandy backshore areas are also found.
he mangrove ecosystems of this ecoregion serve as wildlife refuge, nursery, spawning area, wildlife habitat, nutrient, sediment retention area, and shoreline protection. These features build upon each other to attract many diverse species of wildlife to the ecoregion for the purpose of attaining important resources such as food and shelter. There are numerous special status taxa that are found in the Moist Pacific Coast mangroves ecoregion, denoted variously as Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).
Because of high moisture availability, the salinity gradient is more moderate than in the more northern ecoregion such as the Southern dry Pacific Coast ecoregion. Resulting mangrove vegetation is mixed with that of marshland species such as Dragonsblood Tree (Pterocarpus officinalis), Campnosperma panamensis, Guinea Bactris (Bactris guineensis), and is adjacent to Yolillo Palm (Raphia taedigera) swamp forest, which provides shelter for White-tailed Deer (Odocoileus virginianus) and Mantled Howler Monkeys (Alouatta palliata). Mangrove tree and shrub taxa include Red Mangrove (Rhizophora mangle), Mangle Caballero (R. harrisonii) R. racemosa (up to 45 metres in canopy height), Black Mangrove (Avicennia germinans) and Mangle Salado (A. bicolor), a mangrove tree restricted to the Pacific coastline of Mesoamerica.
Other mangrove species found in the ecoregion are: White Racemosa (Laguncularia racemosa) and Tea Mangrove (Pelliciera rhizophorae), the latter tree requiring some component of freshwater influx into the habitat. A. germinans is also a restricted range tree, occurring strictly in the Costa Rican and Panamanian part of this ecoregion, and stretching slightly into northwestern Colombia. Dominant species change modestly in the southern more humid area of Costa Rica, where P. rhizoporae and R. racemosa thrive. Some other plantlife, which grows in association with mangrove species, is the fern Golden Leatherfern (Acrostichum aureum) and the trumpet tree Mangle Marica (Tabebuia palustris VU).
Two endemic birds listed by IUCN as threatened in conservation status are found in the mangroves of this ecoregion, one being the Mangrove Hummingbird (Amazilia boucardi EN), whose favourite flower is the Tea Mangrove (Pelliciera rhizophorae), the sole mangrove plant pollinated by a vertebrate. Another endemic avain species to the ecoregion is the Yellow-billed Cotinga (Carpodectes antoniae EN). Other birds clearly associated with the mangrove habitat include Roseate Spoonbill (Ajaia ajaja), Gray-necked Wood Rail (Aramides cajanea), Rufous-necked Wood Rail (A. axillaris), Mangrove Black-hawk (Buteogallus anthracinus subtilis),Striated Heron (Butorides striata), Muscovy Duck (Cairina moschata), Boat-billed Heron (Cochlearius cochlearius), American White Ibis (Eudocimus albus), Amazon Kingfisher (Chloroceryle amazona), Mangrove Cuckoo (Coccyzus minor), Yellow Warbler (Setophaga petechia), and Black-necked Stilt (Himantopus mexicanus VU) among other avian taxa.
Mammals although not as numerous as birds, include species such as the Lowland Paca (Agouti paca), Mantled Howler Monkey (Alouatta palliata), White-throated Capuchin (Cebus capucinus), Silky Anteater (Cyclopes didactylus), Central American Otter (Lontra longicaudis annectens), White-tailed Deer (Odocoileus virginianus), feeds on leaves within A. bicolor and L. racemosa forests. Two raccoons: Northern Raccoon (Procyon lotor) and Crab-eating Raccoon (P. cancrivorus) can be found both on the ground and in the canopy consuming crabs and mollusks. The Mexican Collared Anteater (Tamandua mexicana) is also found in the Moist Pacific Coast mangroves.
Reptiles including the Common Basilisk Lizard (Basiliscus basiliscus), Boa Constrictor (Boa constrictor), American Crocodile (Crocodilus acutus), Spectacled Caiman (Caiman crocodilus), Black Spiny-tailed Iguana (Ctenosaura similis) and Common Green Iguana (Iguana iguana) thrive in this mangrove ecoregion. Reptiles here consume fruits, invertebrates, birds, small mammals and even other smaller reptiles.
There are a number of amphibians in the ecoregion, including the anuran taxa: Almirante Robber Frog (Craugastor talamancae); Chiriqui Glass Frog (Cochranella pulverata); Forrer's Grass Frog (Lithobates forreri), who is found along the Pacific versant, and is at the southern limit of its range in this ecoregion. Example salamanders found in the ecoregion are the Colombian Worm Salamander (Oedipina parvipes) and the Gamboa Worm Salamander (Oedipina complex), a lowland organism that is found in the northern end of its range in the ecoregion .
The widespread and extensive destruction of forests in the defined EBA includes major stands of mangroves. This destruction of mangrove ecosystems has caused a decline in available habitat and the resulting decline in species numbers. Sites with the greatest remaining concentrations of mangroves are: Térraba-Sierpe (17,737 hectares); Estero Damas Palo Seco (2312 hectares); Coto Colorado (875 hactares).
A large area is protected in Costa Rica as Corcovado National Park on the Osa Peninsula. This park is also the largest tract of protected land on the Pacific side of Central America.
Ecological threat profile
In general, the river basins are of high topographic relief (i.e., exhibit steep slopes), have seasonally intense rainfall and highly erodable soils, which makes them prone to erosion caused by agricultural practices, deforestation, and livestock overgrazing. The direct result of such erosion is high sedimentation delivered to surface water bodies, which also brings elevated nutrient loads during the rainy season. Even though mangrove soils are too poor with drainage problems and high salinity and acidity preventing the profitable growth of crops, conversion of these lands to agriculture is an ongoing threat to the ecoregion. Agricultural practises also pose a threat due to the use of agrochemicals such as fertilizers, herbicides and pesticides which runoff into the mangrove ecosystems. Lands converted to agriculture are often subsequently abandoned because of high maintenance costs, and an acceleration of erosion.
Another ecological threat is urban encroachment, particularly near Puntarenas and Quepos, which were built in mangrove areas to begin with. Unregulated mangrove cutting for bark and uncontrolled harvesting of the clam "piangua" Anadara tuberculosa have been a threat at least in the past but the government has established quotas and extraction methods, and is preparing a management plan. Bark collectors have had a large impact on the Terraba range because they felled only the largest and most vigorous Rhizopora trees, which also created significant gaps in the canopy. Charcoal production in the Térraba-Sierpe mangrove reserve accounted for 1911 cubic metres of felled timber in 1987. Other threats according to Spalding include exploitation of mangroves for tannin, fuelwood, timber, and charcoal as well as urban development and oil spills such as the 1986 incident.
Justification of ecoregion delineation
Classification and linework for all mangrove ecoregions in Latin America and the Caribbean Basin follow the results of a mangrove ecoregion workshop and subsequent report. The reader should note that this ecoregion can be considered a subset of the World Wildlife Fund ecoregion termed the Southern Mesoamerican Pacific mangroves, which ecoregion can be considered to subsume the Moist Pacific mangroves and continue northward along the Pacific coast into southern Mexico to Oaxaca.
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