Half a million Bangladeshis risk mamu’s displeasure by coming into the Sundarbans each year to harvest its products. They come as fishermen, woodcutters, palm-frond cutters, cutters of thatching grass, harvesters of wild honey. The workers spend weeks at a time in the forest, living off its bounty as they earn a few taka for their labor. Seafood, fruits, medicines, tea, sugar, even the raw materials for beer and cigarettes are to be found in the Sundarbans larder.
Throughout the tropical world it’s the same: Mangrove forests are the supermarkets, lumberyards, fuel depots, and pharmacies of the coastal poor. Yet these forests are being destroyed daily. One of the greatest threats to mangrove survival comes from shrimp farming. At first glance, shrimp might seem the perfect export for a poor country in a hot climate. Rich countries have an insatiable appetite for it (shrimp has overtaken tuna to become America's favorite seafood), and the developing world has the available land and right climate to farm it.
A prime location for shrimp ponds, though, happens to be the shore zone occupied by mangroves, an unhappy conflict of interests that has a predictable outcome: The irresistible force of commerce trumps the all-too-removable mangrove. To compound matters, shrimp farmers typically abandon their ponds after a few crop cycles (to avoid disease outbreaks and declining productivity) and move to new sites, destroying more mangroves as they go.
Mangrove-rich Brazil was slow to stake its claim in the bonanza. By the time shrimp fever hit Brazil’s northeastern states, around the turn of the millennium, shrimp-farming pioneers such as Thailand, the Philippines, and Ecuador had been uprooting their mangroves for decades. Today, in the Brazilian port city of Fortaleza ponds the size of football fields crowd the landscape like rice fields. Paddle wheel aerators froth the water, and workers in kayaks fill feeding trays with fish meal. Even where mangroves have been spared, access to them is often blocked by the shrimp farms.
At the riverside settlement of Porto do Céu—“the gates of paradise”—an electrified fence shuts out villagers from their traditional harvesting grounds. But there is worse. The shrimp ponds have no lining, so salt water has percolated through the sandy soil and contaminated the aquifer beneath. The villagers have been forced to abandon wells that until recently drew sweet fresh water to the surface. The water is no longer sweet; it is salgada, saline, undrinkable.
At Curral Velho, a community to the west of Fortaleza, people have been finding a voice to oppose Big Shrimp. Demonstrations have been organized, land deals challenged, a public education center set up. Sister Mary Alice McCabe, an American nun who is helping the community in its struggle, says that one of the difficulties in raising awareness about carcinicultura—shrimp farming—is that most Brazilians aren’t aware of the environmental damage it causes. “‘Where does it happen, out at sea?’ they ask. ‘No, no, no,’ we tell them, ‘they’re digging up your mangroves, they’re destroying your coastline.’”
As serious as the threat from shrimp farming is to the world’s remaining mangroves, there looms a potentially more disastrous problem: rising sea levels. Standing as they do at the land’s frontiers, mangroves will be the first terrestrial forests to face the encroaching tides.
Loss of mangrove forests could prove catastrophic in ways only now becoming apparent. For more than 25 years Jin Eong Ong, a retired professor of marine and coastal studies in Penang, Malaysia, has been exploring a less obvious mangrove contribution: What role might these forests play in climate change? Ong and his colleagues have been studying the carbon budget of mangroves—the balance sheet that compares all the carbon inputs and outputs of the mangrove ecosystem—and they’ve found that these forests are highly effective carbon sinks. They absorb carbon dioxide, taking carbon out of circulation and reducing the amount of greenhouse gas.
By measuring photosynthesis, sap flow, and other processes in the leaves of the forest canopy, Ong and his team can tell how much carbon is assimilated into mangrove leaves, how much is stored in living trees, and how much eventually makes its way into nearby waterways. The measurements suggest that mangroves may have the highest net productivity of carbon of any natural ecosystem (about a hundred pounds per acre [45 kilograms per 0.4 hectares] per day) and that as much as a third of this may be exported in the form of organic compounds to mudflats. Mangroves, it seems, are carbon factories, and their demolition robs the marine environment of a vital element.
(责任编辑：威展小王)
