By Jennifer Boudart
Mangroves occur in coastal waters at subtropical and tropical latitudes. These woody plants flourish in the intertidal zone, where there is a natural exchange of saltwater and freshwater. They anchor incredibly biodiverse ecosystems that support hundreds of species of wildlife and provide a wealth of valuable ecosystem services. They benefit local economies by providing spawning and nursery habitat for commercially important fish, crabs, and shrimp. They also serve as barriers against storms, reduce coastal erosion, sequester carbon, and improve water quality by filtering contaminants and trapping sediments.
Mexico is among the world's most mangrove-rich countries. Nearly 2 million acres of mangrove swamps are distributed along its Pacific and Gulf coasts. About two-thirds of Mexico's mangroves occur on the Gulf side, primarily on the Yucatán Peninsula. These are important habitats for resident and migratory waterfowl, which are attracted to an abundance of algae and invertebrates found among the mangroves and surrounding beds of aquatic grasses.
Of the 28 priority areas Ducks Unlimited de México (DUMAC) has identified for wintering waterfowl, 21 are coastal ecosystems with intertidal mangrove swamps. Waterfowl species that rely on these habitats include northern shovelers, redheads, canvasbacks, northern pintails, lesser scaup, American wigeon, gadwalls, green-winged teal, and blue-winged teal. In fact, 80 percent of the continental population of blue-winged teal winters in or passes through the mangroves along the Yucatán Peninsula.
Maintaining these ecosystems is crucial to waterfowl, as the abundance of food that these wetlands provide allows waterfowl to rebuild fat reserves and return to their breeding grounds in good condition. Despite being federally protected, mangroves remain vulnerable to negative impacts from human activities that alter the hydrology of these wetlands, and many of the country's mangrove habitats have been lost. When the exchange of saltwater and freshwater is interrupted, the resulting changes in water levels—even by just a few centimeters—along with increases in soil and water salinity, can cause mangroves to die.
To reverse the decline of these vital habitats, DUMAC launched its mangrove restoration program in 1995. As DUMAC Chief Executive Officer Eduardo Carrera explains, "Traditionally, mangrove restoration has centered on planting nursery-raised mangrove seedlings in areas that have suffered some kind of destruction. Unfortunately, most of those seedlings die because the proper hydrology has not been restored. Rather than planting seedlings, DUMAC works to restore the hydrology and reduce salinity levels on its project sites. Mangroves that are still present naturally reestablish themselves within a few years."
Typically, project work involves building culverts or digging channels to restore hydrology. DUMAC hires local people to provide the labor—another innovative feature of the program. "It's very important to involve local people in these efforts. They receive income for the work and develop a sense of ownership," Carrera notes. "They become committed to protecting the area from being damaged again." Completed projects provide other economic opportunities, such as improved subsistence fishing and participation in ecotourism.
Along the Pacific Coast, most DUMAC projects address the impacts of commercial shrimp farming, which has caused extensive mangrove losses. Shrimp farms are often abandoned after only a few years because the soil pH is altered to such an extent that growing shrimp is impossible. DUMAC works in these sites to remove old impoundments, restore the soil pH, and reconfigure the channels to reduce salinity levels. Within a few years, mangroves can become reestablished on these sites.
Most mangrove losses on Mexico's Gulf Coast are the result of changes in hydrology caused by urban development. Mangrove swamps on the Yucatán Peninsula are particularly vulnerable because there are no rivers or lakes to provide freshwater. Construction of roads, ports, hotels, and other infrastructure often cuts mangroves off from freshwater inputs, accelerates sedimentation, and causes salinization.
The Isla Arena Project in Campeche is one of six DUMAC projects completed on the Yucatán Peninsula to reverse these trends. Isla Arena is located within the Ría Celestún Biosphere Reserve, one of the most important wintering areas for waterfowl and shorebirds along the Gulf of Mexico. Through this $1.5 million project, DUMAC has restored the natural hydrology of more than 15,000 acres of coastal mangrove swamps.
Mangroves around Isla Arena had been negatively impacted by a road constructed some four decades earlier. Less than one percent of the road's nearly 10-mile length included culverts to allow freshwater to flow into the mangroves, and those culverts were not placed in areas that coincided with natural drainage. This reduced freshwater inputs; changed the level, frequency, and timing of flooding; and increased salinity in mangrove wetlands.
To address these problems, DUMAC installed seven culverts along the road to restore the exchange of freshwater and saltwater to and from the Gulf. More than 160 local residents were hired to dig nearly 14 miles of channels, which helped increase the freshwater connection and further reduce salinity levels.
In total, DUMAC has restored the hydrology of more than 31,000 acres of wetlands with the subsequent regeneration of 5,500 acres of mangroves in the Yucatán, which represents 20 percent of the mangroves lost in this region. Funding for these projects primarily comes from Mexico's National Forestry Commission (CONAFOR). "We have received funds from CONAFOR for almost every mangrove restoration project we have worked on to date," says DUMAC's assistant director, Gabriela de la Fuente. She says the North American Wetlands Conservation Act is the other main source of funding.
DUMAC's successful conservation of mangrove swamps and other waterfowl habitats in Mexico is crucial to the success of Ducks Unlimited's mission, says DU National Director of Conservation Craig LeSchack. "DUMAC plays an incredible role in Mexico from the standpoint of waterfowl conservation," he observes. "The Mexican federal government and the states recognize DUMAC's expertise. They rely on DUMAC's ability to make their dollars go further so they can deliver more conservation. In turn, DUMAC makes possible DU's continental mission to care for the entire life cycle of waterfowl."