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HUMAN USE OF MANGROVES

Sustainable uses
The mangrove ecosystem has a utilitarian value based on both ‘goods’ (products) and ‘services’ of benefit to humans.
Products from mangrove trees include logs, fuelwood, charcoal, wood-chips, paper pulp, scaffold poles, piling and construction material, stakes for fish traps and fishing platforms, railway sleepers, wood for furniture making and carvings, material for roof thatching, bark for tannin, medicinal products, sugar, alcohol, acetic acid and dyes. Exploitation to obtain products for domestic use has occurred since the beginning of history. Modern exploitation has increased to industrial levels, and the application of proper forest management practices based on cutting cycles and specially designed tree-extraction systems has been necessary in order to maintain a sustainable yield.
In addition to plant products, the mangrove ecosystem can provide a sustainable yield of fish and shellfish if it is not over-exploited.
Services include:
++ stabilization and protection of shorelines;
++ filtering and trapping of water-borne pollutants;
++ provision of nursery and feeding grounds for numerous species of finfish and prawns, and habitat for crabs and molluscs;
++ provision of nesting sites for sea and shore birds; and l provision of resources for tourism and recreation.

Non-sustainable uses
Non-sustainable uses lead to loss of the mangrove habitat, and associated losses of shoreline, organic matter production and species dependent on the habitat and mangrove-based food chains. Mangrove forests may be felled for uses such as aquaculture ponds, salt pans, agricultural use including rice fields, airport and road construction, port and industrial development, resettlement and village development. Canalization and changes in drainage associated with these uses modify the natural water supply and may be detrimental to remaining mangroves.
From the viewpoint of oil spill response, some of the above activities are vulnerable to oil and need to be considered along with the mangrove habitats.
Aquaculture and the use of salt ponds might be particularly affected. Appropriate responses are also needed for port and harbour facilities and associated navigation channels. Aquaculture ponds for fish and crustaceans (prawns and shrimps) have traditionally been excavated in mangrove areas in some parts of the world, notably south-east Asia and South America.
During recent decades, increased aquaculture of crustaceans has been an economic success worldwide, representing, nevertheless, a major problem for mangrove conservation. This is because of the large scale of habitat conversion, with associated changes in the natural tidal flow patterns and the generation of acid conditions (by oxidation of the disturbed sulphide-rich soils) which eventually affect the larvae. These problems can lead to a vicious cycle of mangrove clearing and abandonment called ‘shifting aquaculture’.
Brine evaporation ponds required for salt crystallization are developed mainly by clearcutting mangroves on arid or semi-arid coasts, and significant areas have been destroyed in this way.

In very dry regions, solar evaporation is sufficient to cause crystallization, but under more humid climatic conditions the brine has to be boiled over fires using mostly mangrove wood as fuel, which increases the pressure on the local mangrove resource.
The establishment and expansion of deep-water ports and associated waterways has led to direct loss of mangroves, and erosion. In particular, port facilities located upstream on tropical rivers can have a strong influence on downstream mangrove areas through the permanent dredging activities (and associated dumping of dredge spoil) required to maintain the navigation channels. Dredge spoil may physically smother mangroves, and there may also be an increase of acidity due to oxidation of the sulphide-rich sediment.

mangrove mangrove
Source :
BIOLOGICAL IMPACTS OF OIL POLLUTION: MANGROVES
International Petroleum Industry Environmental Conservation Association

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