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Stemming the tide.

Destruction of the world's mangroves has continued at an alarming rate with devastating results for the indigenous populations involved. While campaigns and action over the last decade have begun to address the problem, Chris Hellier asks whether it's a question of too little, too late to save what remains of our forests of the sea

IN THE MID-19TH CENTURY, an anonymous explorer in northern Australia described the region's mangrove forest as "a greedy usurper that occupies the marshy no-man's-land between dry land and water". Mangroves are one of the least-known ecosystems in the world. Often described as useless swamps or wastelands, these inshore forests play a crucial role in tropical ecology, yet, compared to the great rain forests of the Amazon, West Africa or Southeast Asia, they receive little popular attention. Like the rainforests, however, mangrove forests are in serious decline throughout the world. Recent decades have seen whole swathes of mangroves being cleared to make way for intensive shrimp farms, tourist and hotel developments and to accommodate urban growth. Pollution and timber extraction have also taken their toll. But in areas where mangroves have survived, these unique vegetal frontiers between land and sea have an extraordinary ecosystem.

Some years ago in the Pichavaram mangrove in southern India, I was exploring the marsh's sluggish backwaters in an old dug-out canoe. I was following rhizophora thickets that lined the main channel when my boatman spotted a gap among the tangled prop roots and steered us, slowly, into the heart of the swamp. We left the boat and squelched through ankle-deep mud. Beyond the rhizophora belt lay a second zone of white mangroves with an undergrowth of dwarf shrubs and stunted trees flooded by water which left brown stains around my shins. Two-thirds of the forest was probably covered in this vegetation which gave way to a third area of back mangroves. These consisted of low-growing, dense tufts of halophytic shrubs of the sueda family growing on tiny hillocks. Here, the soil was dry and salty. Only rarely, during an exceptional tide, would it have been inundated by the sea.

All mangrove species are, to varying degrees, salt-tolerant. They thrive in inter-tidal zones, sheltered bays and river estuaries where other plant species find it impossible to survive. They have responded to their unusual environment by developing salt-filtering roots and salt-excreting leaves.

Among the most characteristic species is the red mangrove tree (Rhizophora mucronata), whose intertwined pop roots, exposed at low tide, can grow up to three metres high. Even more interesting is the black mangrove (Avicennia marina), which is anchored into the sand or mud by its long peg roots. Aerial portions, called pneumatophores, reach out of the ground like stalagmites, making it difficult to walk through avicennia thickets. Other species, such as Sonneratia alba, also develop pneumatophores which allow gas exchange, so ventilating the buried portion of the roots. These pneumatophores, which have been known to grow up to 50 centimetres long, in effect breathe air for the mangrove tree.

One of the major ecological benefits of inshore forests is to provide a rich spawning ground for young fish, molluscs and crustaceans. At high tide, hundreds of species of fish use the mangrove to feed and reproduce. Fallen leaves and other detritus may just look like a slimy mulch, but to inshore life this is a luxurious, rich source of essential nutrients. Mangroves also provide nestling sites for coastal birds and are home to mud-skippers and manatees, sea turtles and monitor lizards.

Since humans first settled in coastal areas they have lived in equilibrium with mangrove systems without upsetting the delicate ecological balance. Local communities use mangroves for timber and firewood, and in some cases, such as the arid coastal regions of Kutch in West India, mangrove trees are the villagers only source of fuel. The bark of some species produce dyes and tannin used for treating leather. Others are carved into dug-out canoes or attract honey bees, while a crude alcohol is derived from nypa sap.

Protective beauty

As well as being the provider of useful resources, mangroves protect both the land and sea. Stands of healthy mangrove guard against coastal erosion, at the same time protecting coral reefs and sea grass beds from harmful siltation. Where protective mangroves have been cleared, such as in the Florida wetlands or Durban Bay, artificial sea walls and bulkheads have frequently replaced them.

Over the last 25 years, while significant advances have been made in mangrove research, actual statistics are far from precise. Scientists can't agree on the total area of mangrove forests left in the world, but estimates vary upwards from 100,000 square kilometres, somewhere between the size of Bulgaria and the UK. What is certain, however, is that these forests have declined rapidly. Where they once covered three-quarters of the world's tropical and subtropical coastlines, more than half have been destroyed, with some countries experiencing a very severe rate of destruction. The Philippines has lost about 80 per cent of its mangroves since the 1920s, while Java is believed to have lost almost three-quarters. Thailand has destroyed over half of its mangrove forests in just 30 years.

Human clearances aren't the only factors to have reduced mangrove cover. Natural events have also taken their toll. The Sunderbans (literally beautiful forest) covers 8000 square kilometres at the deltas of the Ganges and Brahmaputra rivers. Home to the rare Bengal tiger, it is the world's largest mangrove forest, yet over the last two centuries the Sunderbans has naturally declined by more than half. The Indian part of the Ganges delta has risen gradually, leaving insufficient fresh water available to leach excessive salts from the soil. The high frequency of violent cyclones in the area also poses an additional threat to the survival of the Sunderbans in that area.

American researchers were the first to raise the problem of mangrove loss in the mid-1970s. As a result some countries, notably Australia, made efforts to protect their mangrove forests. Others, however, continued to ignore the problem. During the 1980s UNESCO and the United Nations Environmental Programme (UNEP) took the lead in mangrove research, encouraging tropical countries to found national mangrove societies. The idea was for each country to produce an action plan to help protect and manage their inshore forests. The results, however, were disappointing. While some countries have designated mangrove reserves, these represent only a small percentage of the total and most mangrove forests are still poorly managed.

Action shrimp

In 1990, this programme was largely ceded to the newly created International Society for Mangrove Ecosystems based at Ryukyus University, Japan. As this was a mainly scientific group, two years later, environment activists founded The Mangrove Action Project (MAP) an international network of 350 non-governmental organisations and over 200 academics, to campaign for the world's mangroves. Since then, much of MAP's efforts have been directed towards the destructive effect of commercial shrimp farms. According to the Choluteca Declaration, signed in Honduras in October 1996, MAP is committed to the conservation of mangroves and against their ill-considered conversion to shrimp farms, an unsustainable activity that is growing in an uncontrolled manner throughout the tropical and subtropical regions of the world. Although there are many reasons for mangrove decline, the main factor of recent times has been the expansion of shrimp aquaculture -- an action often encouraged by international funding. The UN Food and Agriculture Organisation (FAO) estimates that approximately 50 per cent of Asian mangroves lost over the last 20 years is a direct result of large areas being used for shrimp farming. Critics refer to these intensive shrimp farms as slash-and-burn aquaculture. Uncontrolled shrimps farming can be so devastating to the environment that it undermines the industry itself. After harvesting the shrimp, the remaining water is contaminated with shrimp faeces. Low in oxygen and tainted with uneaten food, it also lacks the biological organisms necessary to clean and recycle the water. FAO scientists estimate that 22 hectares of healthy mangrove are needed to cleanse the effluent from a single hectare of intensively farmed shrimp. Yet corporate shrimp farming continues to attract new countries keen to boost their foreign exchange. One of the latest to enter the Asian shrimp market is Vietnam, which has seen its production rise from virtually nil in the late 1980s to about a third of its total seafood exports today. Over a similar period, Vietnam's two southern provinces have lost around two-thirds of their mangrove forests.

Shrimp farming is a boom-bust, get-rich-quick industry. In Vietnam, it is estimated that farmers can make $2,000 per hectare per year at the cost of destroying mangroves which may yield only $300 a year. After four or five years, however, the environment can no longer take the strain of intensive farms. Pods are frequently abandoned when they are of no further use, and farmers move on elsewhere. The financial benefits of this intensive farming are also limited to industrial-scale farmers, corporate interests, investors and exporters.

According to Anuradha Wickramasinghe, director of the Mangrove Conservation and Demonstration Centre in Sri Lanka, traditional fishermen in Puttlam lost their livelihood following the establishment of commercial shrimp farms in 1994. Until then, 28,000 fishermen had depended on the adjacent lagoon. Two-thirds of the fisherfolk have now lost their livelihood and migrated to urban areas to look for alternative jobs, Mr Wickramasinghe explains.

And, as is often the case in such matters, the negative effects of these commercial shrimp farms and mangrove destruction are borne by the indigenous communities, while western consumers of such developing world products inadvertently contribute to the problems and policies they criticise. Saturday night's shrimp starter may well have come from a former mangrove swamp. As Alfredo Quarto, co-director of MAP, points out, the fate of the remaining mangrove forests may now rest in the hands of consumers from the wealthy nations that import luxury shrimp products.

Other fish to fry

There are alternatives to intensive shrimp farms. Researchers have recently begun to promote mangrove-friendly aquaculture, smaller-scale projects where shrimps are farmed in association with existing mangrove areas. Inshore enclosures include mangrove trees growing on small mounds. The farmed fish or shrimp benefit from the mangrove nutrients, while the prop and aerial roots provide shelter for small fry. Indonesia, home to about a quarter of the world's mangroves, is at the forefront of this mangrove-friendly system. Also known as silvofishery, or locally empang perit, it is based on a centuries-old traditional system which allows for 60 to 80 per cent of mangrove cover within the fish dykes. Several research projects are currently underway in the country including three demonstration sites in South Sulawesi. According to its supporters, empang petit is appropriate for small-scale family operations and a viable alternative to intensive shrimp ponds.

Isolated, however, this is not enough and other management policies are also needed. In forests where indiscriminate cutting has killed many trees and destroyed entire mangrove habitats, sustainable techniques could be applied. Indeed much of this degradation is unnecessary since some mangrove species can be successfully coppiced to proved a long-term harvest. What is required, says Adelaide Semesi of Dar es Salaam University, Tanzania, are integrated education policies involving local communities.

Changing attitudes and policies towards mangrove management is a slow process, but there are encouraging signs of change that are beginning to emerge. In Costa Rica, MAP and local environmentalists have succeeded in reversing a congress decision to open up protected mangrove forest for expanded shrimp farms. In Florida, the Mangrove Replenishment Initiative is having some success in repairing former mangrove areas in the US state's remarkable estuary system. Even in Thailand, the world's largest farmed shrimp producer with about a quarter of the market, local initiatives are encouraging a move away from intensive aquaculture techniques. In the country's southwest, the Yad Fon, or Rain Drop Association is promoting community mangrove forests with 30 target villages where fishermen are being encouraged to conserve and restore their coastal resources.

Government figures indicate that the rate of mangrove loss in Thailand has been lower during the 1990s than at any time in the previous 30 years. According to Green-peace, the country may now have reached its upper limit of shrimp production. But even at the current lower rate, if mangrove conversion continues, MAP estimates that all of Thailand's mangroves will have disappeared in the next 50 years. It's a haunting prospect.
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Title Annotation:protecting the world's mangroves, forests of the sea
Author:Hellier, Chris
Date:Jun 1, 1999
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