Mangrove Threats and Solutions
Straddling land and sea and teeming with life, mangrove forests are key to healthy coastal ecosystems, but it is only in the last few decades that people have begun to realize their importance. Ironically, during this same period, mangroves have disappeared with alarming speed. By some estimates, less than 50 percent of the world's mangrove forests were intact at the end of the 20th century, and half of those that remain are in poor condition. Mangrove forests are among the most threatened habitats in the world, and mangrove loss is rampant across the globe. Thailand has lost 84 percent of its mangroves, the highest rate of mangrove loss of any nation, while the Ivory Coast, Guinea-Bissau, Tanzania, Mexico, Panama, Malaysia, Myanmar, Pakistan, and the Philippines have each lost more than 60 percent of their mangrove forests. Most mangroves grow on public land, only about 1 percent of which receives any sort of protection. Even where some legal designation or protection is in place, preserving mangroves is difficult because of development in the form of:
By far the greatest threat to the world's mangrove forests is the rapidly expanding shrimp aquaculture industry. Hundreds of thousands of acres of lush wetlands have been cleared to make room for artificial ponds that are densely stocked with shrimp. Shrimp farmers dig channels to supply the ponds with enormous quantities of freshwater and seawater. These water diversions alter the natural flow of water that maintains the health of surrounding mangroves as well as ecosystems farther inland and offshore. Diverting water can harm mangroves by preventing their seeds from being dispersed via seawater, and it can kill the trees by cutting off freshwater supplies. When diverted inland, seawater may contaminate farmland or freshwater below the ground. Shrimp farmers also use massive amounts of chemicals and antibiotics to keep the overcrowded shrimp healthy. This chemical soup, along with enormous quantities of organic waste, contaminate surrounding freshwater and coastal waters. In addition, the process of catching wild shrimp larvae to stock the ponds is hugely wasteful. Fishermen use nets that damage the ocean floor and trap many species besides shrimp, leaving marine habitats damaged and local fisheries depleted. The social costs of shrimp aquaculture are also high. Rather than bolster local economies, shrimp farming can actually deplete the local peoples' ability to support themselves. Because shrimp is a cash crop, not a subsistence crop, the profits from shrimp farming are exported, and the jobs it generates are usually temporary. The average Asian intensive shrimp farm survives only two to five years before pollution and disease force it to shut down. Local people are left with a devastated landscape that can no longer support fishing, farming, or wood gathering, and many are forced to move away.
Tourism is a booming industry and an important source of income in many developing nations. Unfortunately, irresponsible tourism can destroy the very resources people are coming to see. As tourists hike, drive, or paddle into once-remote areas, they bring with them garbage, sewage, noise, fumes, lights, and other disturbances that can damage mangroves and the surrounding ecosystems. Walking off paths, lighting fires, feeding wildlife, anchoring on reefs, and collecting shells and plants are also destructive. Tourism can be sustainable when groups are small and people leave the habitat the way the found it.
Many thousands of acres of mangrove forest have been destroyed to make way for rice paddies, rubber trees, palm oil plantations, and other forms of agriculture. Farmers often use fertilizers and chemicals, and runoff containing these pollutants makes its way into water supplies. Despite their resilience, mangroves can tolerate only a limited amount of industrial and agricultural pollution without dying. In addition, waterways are often diverted for irrigation or paved over for roadways, which alter the natural flow of water. Because mangrove forests are adapted to tidal fluctuations, they can be destroyed by such changes to their habitats.
Coastal development takes many forms, from ports and docks to hotels, golf courses, marinas, and convention halls. Everyone loves being near the sea, but as streams and wetlands are filled by roads and concrete, they can no longer process natural chemicals. Worse still, pollutants that accompany development can damage individual trees or whole tracts of mangroves. With buildings come people, traffic, garbage, and noise, each of which takes its toll on the plants and animals that inhabit rich coastal ecosystems.
Charcoal and Lumber Industries
Chopping down mangroves for charcoal and timber is an important cottage industry for many coastal communities. Mangrove wood is used for building material, fencing, and fuel. It also yields valuable, high-quality charcoal. In places where fishing has declined below subsistence levels, many people have turned to charcoal production for their livelihood, which furthers the cycle of habitat loss and fishery decline.
More and more people around the world are organizing to protect and restore these ecologically, biologically, and culturally diverse coastal forests. Heightened awareness of the importance of mangroves has led to projects ranging from small-scale mangrove replanting efforts to replumbing the Everglades. Communities around the world are learning how to protect mangroves and use them in sustainable ways.
More About This Resource...
Our innovative Science Bulletins are an online and exhibition program that offers the public a window into the excitement of scientific discovery. This essay was published in May 2004 as part of the Mangroves: The Roots of the Sea Bio Feature.
- It opens by stating that, straddling land and sea and teeming with life, mangrove forests are key to healthy coastal ecosystems.
- It then looks at how mangrove loss is rampant across the globe, detailing development threats.
Supplement a study of biology with a classroom activity drawn from this Science Bulletin essay.
- Have students read the essay (either online or a printed copy).
- Have students write a brief reaction to the essay, explaining in their own words why mangroves are among the most threatened habitats in the world.