Michael Richardson: Invasion of the biodiversity snatchers

It sounded like an innocuous tip-off call after someone last month saw a lone marron - a freshwater crayfish native to Australia - on the footpath outside a disused service station in West Auckland. But New Zealand biosecurity officers investigated immediately.

In the service station and a pond at South Head in Kaipara, they found more marron and some gudgeon, a small baitfish used by freshwater coarse fishermen.

Both marrons and gudgeon (a voracious carnivore with a liking for small native fish) are banned as unwanted organisms under the 1993 Biosecurity Act.

Officials of Biosecurity NZ are now checking to see if either species managed to get into the country's waterways.

The discovery is just one example of the rapid spread round the world of so-called invasive alien species. New Zealand has suffered from imported possums, rabbits and many others but is no unique victim. This is a dark side of globalisation, one that increasingly affects even previously isolated island-nations. The losses caused to global agriculture, forests, fisheries, marine areas, the natural environment, native flora and fauna, and biodiversity are already huge.

The United States Government estimates that the annual bill from invasive species, including eradication and protection measures, in the US alone is more than US$100 billion ($136 billion).

Invasive plant species cover an estimated 40 million hectares in the US and are spreading annually across 1.2 million additional hectares. They reduce crop and stock yields, and degrade marine and freshwater ecosystems.

"Few people recognise how profoundly invasive alien species have reshaped the natural landscape around them over the past decades and centuries," says Klaus Toepfer, executive director of the United Nations Environment Programme.

"From tree-killing diseases to rats and other alien predators, invasives have travelled with traders, emigrants and now tourists to new lands where the native species have not had time to evolve adequate protections against these sudden threats.

"As globalisation continues to accelerate, the risks can only grow."

Alarmed at the potential damage to its inland fisheries, the US said a few years ago that it would ban imports of an unusual fish from Asia and Africa that is prized for its supposedly powerful medicinal properties, particularly by Asians living in America.

Known as the snakehead, this freshwater fish has razor-sharp teeth and a voracious appetite, often consuming all other fish in a lake, pond or river. It reproduces quickly and can slither across land and live out of water for at least three days.

"These fish are like something from a bad horror movie," US Interior Secretary Gale Norton said as she announced the plan to prohibit the importing or sale across state lines of 28 species of snakehead. A 2001 study by the Fish and Wildlife Service found that snakeheads had been discovered in seven states and established reproducing populations in two of them - Florida and Hawaii. About 17,000 snakeheads were imported into the US between 1997 and 2000 by seafood sellers and aquarium shops.

The problem of travelling species is not new. As humans started to explore they often took along or brought back with them, deliberately or inadvertently, new species. Sheep, deer, cats and rats are just a few examples.

But as the pace of globalisation has intensified in recent decades, the movement of species has become much more widespread.

David Barnes, a marine biologist at the British Antarctic Survey organisation, spent 10 years studying 30 remote islands from the Arctic to the Antarctic for evidence of marine organisms travelling the world on flotillas of discarded plastic and other human-made rubbish. He reported his findings in the science journal Nature in April 2002.

Alien species ride on many kinds of transport and export goods, including timber, farm produce and nursery plants. Marine organisms frequently move via ships, either on their hulls or in their ballast water. At least 148 marine invaders are now found in New Zealand waters, most arriving in the last 40 years.

But Dr Barnes said his study pointed to floating rubbish as "the most common sea-going transport system and is responsible for the widespread distribution of many marine animals that use it to hitch a ride".

After habitat loss, biological invasion constitutes the greatest threat to biodiversity and it has already had devastating consequences for the planet, says Jeffrey A. McNeely, chief scientist of the IUCN, the World Conservation Union. It brings together nearly 80 states, more than 100 Government agencies, and more than 750 non-government organisations and 10,000 scientists and experts.

It published a report in 2001 that listed 100 of the world's worst invasive species. They include the crazy ant, brown tree snake, small Indian mongoose, Nile perch, strawberry guava, water hyacinth, zebra mussel, brushtailed possum, grey squirrel, domestic cat, Indian myna bird, Asian longhorned beetle, sweet potato whitefly, Asian tiger mosquito, yellow Himalayan raspberry, Koster's curse, mimosa, shoebutton ardisia, red-vented bulbul, erect prickly pear and the mile-a-minute weed.

Crazy ants, so-called because of their frenetic movements, have invaded ecosystems and caused extensive damage from Hawaii to the Seychelles and Zanzibar.

On Australia's Christmas Island, in the Indian Ocean, vast armies of ants devoured the unique land crabs, at one point killing up to half the population of about 80 million, said David Slip, the island's official conservator.

The crabs, blinded by formic acid squirted by the ants, were quickly overwhelmed, partly eaten and left in rotting piles on the forest floor. It was only this year, after an expensive ant control campaign, that baby crabs started to appear again in large numbers.

Crazy ants, fire ants and Argentine ants are high on New Zealand's biosecurity watch list.

China, too, is alarmed by foreign ants. Hong Kong has been battling to stop the spread of red fire ants, whose fiery sting can be fatal to humans, since they were first found there in January. The insects have moved into the neighbouring Chinese province of Guangdong.

The beautiful purple and violet flowers of the South American water hyacinth make it a popular ornamental plant. Yet it is one of the worst aquatic weeds in the world, blocking waterways, interfering with boat traffic, swimming and fishing.

Clearly, well-organised and funded national biosecurity systems are vital, especially in countries such as New Zealand and Australia where farming is an important source of export income and foreign tourists are attracted by unique flora and fauna.

But Hamdullah Zedan, executive secretary of the Convention on Biological Diversity, says that a more effective international system to prevent bio-invasions in all areas of the world is also urgently needed.

* Michael Richardson, a former Asia editor of the International Herald Tribune, is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore and a columnist for the Herald.