Rabbits, mussels, hyacinths among alien invaders


STOCKHOLM – Alien species piggybacking on human travellers to new countries are wreaking havoc on planet earth in the harmless-sounding guises of fluffy rabbits, violet water hyacinths and humble zebra mussels.

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 travelling to the Pacific islands. Ballast water dumped from ships is often to blame, containing thousands of stowaways.

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.

“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 Programme. “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.

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 jelly fish, mussels or crabs can be sucked up and dumped thousands of kilometres away. Ocean-going ships give creatures that can only live in cool waters a route across the tropics from the northern to southern hemispheres.

The U.N.’s International Maritime Organization, based in London, is set to work out new ballast guidelines at talks from February 9 to 13. One proposal is for ships to take on and discharge water at least 200 nautical miles from land.

Other research has focused on better water filters, sterilisation by ozone, ultraviolet light, heat or electric currents to kill organisms travelling in ballast water.

And Norwegian-based ship classification group Norske Veritas has produced a water database giving risks of organisms surviving. Fresh water organisms sucked up near an estuary in the Netherlands, for instance, may have scant chance of surviving if dumped in the salty Pacific off Sydney.