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ANTHONY RICCIARDI AND HUGH MACISAAC

The Globe and Mail, May 16, 2007

A virus is causing mass die-offs of fish in the Great Lakes, the world's largest freshwater fishery. The virus is one of nearly 200 alien species that have invaded the region.

On the Prairies, farmers are battling leafy spurge — a weed toxic to cattle, while city-dwellers are witnessing the western spread of Dutch elm disease. On Vancouver Island, a tropical fungus from Australia has caused fatal infections in animals and humans.

These are not isolated horror stories. They are symptoms of a worldwide phenomenon: a form of human-driven global change described by the prestigious scientific journal Nature as "the world's largest environmental problem."

Thousands of alien species of animals, plants, bacteria and fungi have become established across the planet. Although species have spread into new areas throughout history, they now do so at unprecedented rates and distances they couldn't accomplish without human assistance.

Human travel and trade have created a borderless world for hitchhiking organisms — a biological global village.

Many alien species are harmless, or even beneficial. But some reproduce prolifically in the absence of natural predators and diseases. These pests can cause significant ecological and economic damage, and harm human, plant and animal health alike.

Next to habitat destruction, alien species are the leading cause of extinctions worldwide and are eroding Canada's biodiversity. Introduced rats eat the eggs and nestlings of ancient murrelets and other seabirds living on the Queen Charlotte Islands. The sea lamprey incursion into the Great Lakes led to the extinctions of three native fishes.

A U.S. study estimated the damage and control costs of invaders in that country to be $120-billion (U.S.) annually. We have a poor understanding of their economic impact in Canada, but the data show our resource-based economy is suffering under the onslaught. Precise estimates are elusive: Most invasions are not monitored; even the impact of well-known invaders like zebra mussels is poorly documented.

Essentially, every alien species that crosses our borders is a potential hidden tax, which — like most taxes — will likely never be removed and whose cost will increase with time.

Once established, alien species may threaten our exports. This was shown by a ban on PEI potatoes by the U.S. in 1999, when a single field of potatoes was found infected with an alien fungus. This incident cost Canadian taxpayers more than $80-million.

The problem will worsen with climate change. A warmer climate will allow alien pathogens and the insects that carry them to thrive in new environments. This has already happened with the spread of a tropical livestock virus into northern Europe last summer, when the average temperature — the hottest on record — was 4 C above normal. The virus causes "bluetongue disease" in sheep and cattle, and brought to a halt exports of livestock from the Netherlands.

Much needs to be done. A national strategy to address alien species, led by Environment Canada and initiated in 2001, is still not fully funded and implemented. The Canadian Food Inspection Agency serves a vital role to ensure commodity imports are free of alien species, but it is not sufficiently staffed to protect against all future threats. Funding should be commensurate to the scale of the problem and requires a commitment by federal and provincial governments. We need to develop biosecurity programs to identify and eliminate the vectors that deliver alien species to our country. We must also increase our capacity to detect new threats early and determine appropriate emergency responses.

The nation that can most effectively deal with alien species will have an economic advantage in the biological global village.

Anthony Ricciardi is a professor of environmental science at Ï㽶ÊÓƵ; Hugh MacIsaac is a professor at the Great Lakes Institute for Environmental Research, University of Windsor.