Hungry snail threatens Asian wetlands

”Ecologic disaster looms in the wetlands of Laos and Thailand. It is high time for the world to react,” says Swedish researcher Nils O L Carlsson at Lund University.
     The culprit is the plant eating Golden Apple Snail.
     While the sleamy animal’s ravages in rice fields are well known in Asia, the snail’s highly damaging effect on the regional wetlands’ species-rich ecology have been virtually overlooked until now.
     Golden apple snails were originally imported in 1980 as a delicatessen to Taiwan by traders from South America.
     The meaty, large snail was to be farmed and sold to Taiwanese gourmets.
     But the bright business idea turned to ecologic nightmare when the fast breeding snail fled from farms in Taiwan and conquered rice fields, irrigation channels and wetlands. It ate all plants in its way. In five years time the Golden Apple Snail had migrated to Japan, China and the Philippines. Since then it has spread further, to South East Asia, north Australia, Hawaii and southern United States.
     It has devastated rice farms everywhere.
     And now fresh research by Nils Carlsson shows that the wetlands in Laos and Thailand, an important source of food for low income earners and the poor, and habitat for a broad range of animal and plant species, are equally devastated.
     ”One snail lays some 300 eggs a week. In the wetlands you encounter naked plants and bushes, where snails have consumed all leaves and greenery, covered in a pink blanket of eggs,” says Nils Carlsson.”As much as 300 000 eggs on a single bush is common.”
     When the snail hit rice fields, farmers responded with powerful pesticides.
This gave birth to a environmental disaster.
     ”All kinds of pesticides, approved and outlawed, are readily available in Laos and Thailand and they are cheap. Besides huge negative effects on all living creatures in rice fields are poisons a shortsighted solution. The snail’s eggs are above the water surface and make it anyway. On top of that does rains and floodings pave the way for new healthy snails to migrate in to the rice fields at the same time as poisons leak out in channels and wetlands. And nobody knows how much chemical residue that remain in rice and other farmed water plants consumed by humans, ”comments Nils Carlsson.
     The rice field problems have up to now overshadowed the other big issue: that this snail eat all water plants in the wetlands and causes unnatural algae growth and reduced water quality.
     ”Ironically it has been completely silent about the snails´ ravages in the natural wetlands. They were not seen as causing any economical damage,” continues Nils Carlsson who has researched wetlands in Laos and Thailand.
     The alarming findings are presented in his doctoral disputation ´Invading Herbivory. Effects of the Golden Apple Snail in Asian wetlands´ at Lund University on 16 April.
     ”But the wetlands are very important, both for animals and for those poor people that live outside the ordinary economic system. For them these areas constitute important food reserves. Humans get drinking water there and they do not only catch small fish and crabs but do also use water plants as food, building material and animal feed. When the snails consume all plants, these productive wetlands transform into overfertilised, algae filled ponds,” claims Nils Carlsson.
     When snails eat plants in the wetlands, nutrients otherwise absorbed by the plants are released in the water and daylight reach further down the water.
     This gives plankton room to move around and the nutrient rich water thickens to a tight visible biomass which prevents plants from returning.
     At the same time do animal life decrease as there is no longer any plants around, protecting fish fry and eggs.
     In addition is most sewage water from small villages here not treated. This nutrition rich sewage goes right into the wetlands where the nutrients should be absorbed by fast growing plants that in turn is harvested as human food and animal feed.
     ”But as the snail consumes all water plants, and the same amount of nutrients still enter the wetlands, the end result is a ecologic and local economic disaster of large proportions,” explains Nils Carlsson.
     The original idea to eat the snail is no good either, concludes Nils Carlsson.
     ”Many poor have turned to eat golden apple snails. I have tried to inform people about the risks. Snails must be very well cooked in order to kill possible parasites in them. This snail sometimes hosts a worm, a parasite that migrates to the human brain and kills the carrier.”
     Quite serious information given a common misconception in Laos that the snail has poisonous eyes, and as long as you take away the eyes you can eat the snail half cooked…
     Nils Carlsson´s research shows that snail invaded wetlands may contain ten snails per square meter, well equal to the snail density in rice fields.
     ”I meet many people with bleeding feet in the rice fields. Snail shells are everywhere. You easily cut yourself on them while working bare feet in rice fields. The risk for infections and parasites do also increase,” says Nils Carlsson.
     But there are ways to fight the snails with natural means.
     Trials in Laos show that at least four fish species, a turtle and a freshwater crab eat the snails. And the open billed stork in Thailand is another snail predator.
     That the natural snail enemies have no measurable effect on the snails yet may be due to heavy fishing and hunting.
     One may also pick snails in rice fields and wetlands and convert them to animal feed as way to decrease the numbers.
     ”My research shows there are natural enemies available. We need more research about that matter. Furthermore we must inform people that you cannot fish, hunt or poison these species if you want to have any effect at all by the snail’s natural enemies. More and deeper studies would prove that there are good reasons to sustain biodiversity in South East Asia. It is much better to fight the snails with its natural enemies than using pesticides!” ends Nils Carlsson.

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