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19 October 1998 |
Ref 98/241 |
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Golden apple snails can make attractive aquarium pets, but they have left a trail of destruction across South East Asia and now they are threatening Australia.
The warning comes from Dr Geoff Baker, an authority on molluscs and worms from CSIRO Entomology, who fears that Australia's rivers and ricefields could be next to suffer from the voracious and uncontrollable South American pest.
In a recent paper to the Australian Applied Entomology Research Conference, Dr Baker said some close relatives of golden apple snails were already on sale at aquarium shops across Australia.
"These snails, often called mystery snails, may not pose a major threat to Australian ecosystems. The problem is we have very little data to be sure."
More disturbing, says Dr Baker, is the fact that mystery snails are very hard to tell apart from their close relative, the golden apple snail, Pomacea canaliculata.
"This species has become a major pest of rice throughout Asia and is now widespread on Australia's northern doorstep.
"If it is established in Australia - and we will have trouble detecting this because of its visual similarity to the mystery snails - it has the potential to spread across the continent, invading and ravaging our native river systems and $500 million rice export industry.
"Golden apple snails are attractive to look at, and they keep the slime off the inside of your fish tank - which is why they've been touted elsewhere round the world by the aquarium trade. But if they ever get into our rivers they could cause havoc," Dr Baker says.
Golden apple snails grow to a substantial size - as large as a golf ball or even a tennis ball in some cases. Imported into Taiwan and the Philippines as "the Asian escargot" they not only failed the taste test, but then began to destroy huge tonnages of the rice crop.
Today, says Dr Baker, they are the number one pest of rice, and are causing horrific amounts of toxic pesticide to be used in waterways and paddyfields in a vain effort to control them. The pesticides in turn are wiping out harmless native wildlife.
Over the last 15 years the snails have found their way into the waterways of Japan, China, Indonesia, Thailand, Vietnam, Laos, Cambodia, Malaysia and Papua New Guinea.
Analysis on where the snail could spread in Australia, based on its native climatic range in Brazil, Argentina, Ururguay and Paraguay, is chilling. Most of the east coast from Adelaide to Rockhampton is vulnerable, as is the Top End, Cape York and the southwest of Western Australia, according to CSIRO Entomology's CLIMEX prediction program.
Australian aquarium shops across the continent are already selling the mystery snail P.bridgesi, says Dr Baker.
"I showed several specimens of this snail to the world's leading authority, and he had difficulty in differentiating them from P. canaliculata, which is the really bad pest.
"If he couldn't easily tell them apart, this makes it quite likely that P.canaliculata could also sneak into Australia, mistaken for P. bridgesi. Golden apple snails have been intercepted by Australian quarantine inspectors in the past, and mystery snails are being bred in outdoor ponds here."
Dr Baker's concern is that the snails, with their broad appetite for water plants such as lotus, water chestnuts and taro as well as rice, could become another cane toad or carp, inflicting a fresh eco-shock on Australia's already ravaged waterways and their beleaguered native species.
"The Murrumbidgee Irrigation Area, with its $500m rice export industry, is clearly at risk. So too are places such as Kakadu," he adds.
"My fear is that they could prove unstoppable in our environment. We cannot hand-harvest them, as they do in Asia. Drenching our rivers in pesticide is out of the question. Nor can we hope to control them mechanically, with screens or by changing water depth, as farmers try to do in Asia," he says.
There may be ways to keep the snails in check using natural biological control agents, but so far nothing is known of these.
In fact, says Dr Baker, we don't even know the most basic facts about the snails' taxonomy and population ecology. Without this information it is hard to assess the scale of the threat, let alone start looking for ways to prevent it.
More information:
Dr Geoff Baker, CSIRO Entomology 02 6246 4406
Malcolm Robertson, CSIRO Entomology 02 6246 4040
Picture/vision opportunity:
Dr Baker has specimens of apple snails in his laboratory. These
are about 4-6cm in diameter.
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