By Catheryn Thompson
Vudthikorn Chittiwan is a lecturer in aquatic science at Prince of Songkla University in south Thailand. He has a scholarship from the Australian government to study the environmental impacts of prawn farming on mangrove ecosystems in southern Thailand.
Mangroves live in coastal areas where animals and vegetation are specially adapted to the inter-tidal environment.
Mangrove leaves are rich in organic matter, and the swamps provide a perfect habitat for the breeding and raising of many animals (which is crucial for the local people). The mangroves act as a buffer against cyclones, and they are able to absorb many pollutants, including waste water from the local community. They can even absorb oil.
The timber is used for fuel, cheap housing construction, charcoal, fishing equipment and glue. They are used as fodder and fertiliser in agriculture. Paper, foods, medicines, beverages and fibres are all direct products from mangroves. Indirectly the mangroves provide food and habitat for fish, crustaceans, molluscs, birds and bees.
Prawn farming initially began in central Thailand, with exports mainly to Japan. It relies on the farmers feeding the prawn in a pond for approximately five months. Waste feed and prawn excrement (which contains high levels of nitrites, ammonia and hydrogen sulfide) pollute the marine environment.
The ponds are flushed daily with seawater at high tide. Potentially harmful chemicals, antibiotics and fish-killer are washed out of the ponds and into the sea. Water pollution caused prawn farming in central Thailand to collapse. The farming shifted to southern Thailand but the practices continued.
The life span of a pond is four to five years due to the build-up of organic substances on the bottom of the pond, which becomes putrid with hydrogen sulfide. Tidal flush doesn't help with the pollution problem because the water just circulates between the different farms and depletes the water quality over a wider area. Vud says this may be partly ameliorated by better farm layout.
As the prawn farms are constructed, the mangrove swamps are clear-felled. It is done very quickly at night because it's illegal. (The mangrove swamps are government-owned.)
People with power and money support prawn farming by providing the equipment to clear-fell the mangrove at an accelerated rate. It has been predicted that the mangrove in Thailand will be entirely eliminated in 10 years if the present rate of clear-felling continues.
Concerned people are trying to raise the awareness of the local people so that they can help slow down the process. Regional forestry officers are patrolling the area, trying to enforce the law. The Royal Forest Department is replanting mangrove seedlings in the deforested and mudflat areas. This has been quite successful but the clear-felling is outstripping the replacement, as a mature mangrove swamp takes at least 10 years to grow.
Vud hopes that his research may help in stopping the over-exploitation of the mangrove. He may be contacted on (002) 202 839 at the University of Tasmania.