Rabbits, Mussels, Hyacinths Among Alien Invaders
Date: 05-Feb-04
Country: SWEDEN
Author: Alister Doyle
Helped by their lethal skill of hitch-hiking with humans, organisms from algae to rats are destroying habitats of other creatures and plants, driving some to extinction and causing tens of billions of dollars in damage each year.
And no one has worked out how best to combat what the United Nations calls "invasive alien species," one of the main threats to biodiversity on earth along with global warming and human destruction of natural habitats.
Hawaii, for instance, reckons it gets about 20 new species every year against one every 70,000 years before people started traveling to the Pacific islands. Ballast water dumped from ships is often to blame, containing thousands of stowaways.
"Efforts to control invaders are looking pretty bleak," said Greg Sherley, head of the Global Invasive Species Program (GISP) Secretariat in South Africa, pointing to scant successes like eradication of rats from New Zealand's Campbell Island.
A U.N. meeting in Malaysia from February 9 to 20 will study efforts to reach a U.N. goal of a "significant reduction" in the rate of biodiversity loss by 2010, including ways to curb invasion by species that flourish when freed of predators back home.
But which is the worst alien species?
Given a vote, most animals and plants on earth - and extinct creatures from the dodo to the woolly mammoth - would probably give "homo sapiens" an overwhelming win. But humans are usually excluded.
AIDS? SARS?
"In terms of the impact on modern human well-being it is almost certain to be a pathogen, like HIV," said Professor Charles Perrings of the environmental department at the University of York, England. Human travel is crucial for the spread of illnesses ranging from SARS to flu.
But most overviews of alien species exclude those that only affect human health or crops and focus on organisms, normally transported by people, that take over native ecosystems.
"My vote goes to the rabbit," said Will Steffen, executive director of the International Geosphere-Biosphere Program. "But that may be because I'm Australian."
Rabbits have displaced many native animals and plants in Australia by breeding unfettered by predators like foxes that keep them in check in Europe.
"The water hyacinth ranks high on my list," said Anne Larigauderie of the Diversitas Secretariat based in Paris. She has a doctorate in the study of the purple-flowered plant choking lakes in Africa, far from its South American home by the Amazon.
The plant, whose leaves float on the water, blocks sunlight and kills plants and fish below. African nations have turned to trying to mash them up with machines called "swamp devils" or to deploy beetles to prey on the plants.
In North America, official estimates show that zebra mussels native to Russia and brought by ballast water are likely to cause up to $5 billion worth of damage in a decade to the Great Lakes alone by clogging piers and water pipes.
One overview of 100 of the "world's worst invasive alien species" also lists infamous species like the crazy ant, the brown tree snake and the Nile perch.
RAT-EATING MONGOOSE
The study, by the Invasive Species Specialist Group, also highlights the small Indian mongoose, introduced to islands from Mauritius to Hawaii in a bid to control alien rats. It ate the rats and took over their niche as a top predator.
"At a global scale, rats would be a major contender" for the title of the alien that has wiped out most species, said Graham Surrey of the ISSG. Red fire ants, zebra mussels and water hyacinth were among those causing most costly damage for humans.
U.N. documents for the Malaysia meeting glumly say that "eradication of an already established species is extremely difficult, if not impossible."
Experts say the best hopes may lie in anything from public education to tighter quarantine rules. One big measure is to improve controls on water taken on as ballast to help keep ships stable.
Organisms from eggs of jell