January 24, 2006
Costly alien invaders rock world’s balance
By Lucas van Grinsven
AMSTERDAM (Reuters) - Blue-collar workers in Europe and the
United States who feel threatened by Asian rivals should spare
a thought for local birds, crabs and oysters, also facing
competition from more efficient eastern species.
Dull-colored pigeons, starlings and crows used to dominate
the skies above Amsterdam, but these days citizens might spot
the brilliant green plumage of a long-tailed tropical parakeet.
Originally from Asia, 1,200 collar parakeets now live in
the Dutch capital, descendants of a small group whose owner,
driven mad by their constant chatter, set them free in the late
The parakeets are among many species -- from Asia and
elsewhere -- that have relocated as increased world trade has
facilitated the movement of "invasive alien species."
This biological globalization is recognized as a major
threat to biodiversity, second only to habitat destruction, and
conservationists and scientists are seeking ways to curb, or at
the very least, monitor these movements.
Annie Simpson of Global Invasive Species Information
Network (GISIN), says scientists estimate that up to 5 percent
of the world's gross domestic product is being destroyed as a
result of foreign pests and other invasive species.
The invaders can destroy habitats and drive endemic species
to extinction. In Amsterdam, woodpeckers are being driven out
of tree holes by the parakeets.
"A parakeet pushing out a woodpecker is peanuts compared
with the economic damage done by other invasive species," said
Amsterdam ecologist Remco Daalder.
Researchers have estimated the United States alone spends
$137 billion each year fighting immigrant flora and fauna, a
figure that rises to $336 billion when Britain, Australia,
India, South Africa and Brazil are included.
The World Conservation Union says uncertainty exists about
the total economic costs, but estimates of the costs of
particular species to particular sectors show a serious
Environment ministers will meet in Curitiba, Brazil, from
March 20-31, for United Nations talks to protect animals and
plants from threats like pollution, global warming and
HUMANS TO BLAME
Invaders are a global problem: the Nile perch has wiped out
endemic fish in Africa's Lake Victoria; commercial fishing in
the Black Sea collapsed after the arrival of plankton-eating
North American jellyfish; and the European zebra mussel causes
$5 billion of damage a year to American industrial plants.
In most cases, humans have themselves to blame.
In the 1960s, European oyster farmers introduced Japanese
oysters to the cold North Sea after heavy frost killed off most
of the native species. The Asian shellfish started to thrive.
Driven north by the currents and without a natural enemy
because birds cannot open them, the oysters are squeezing out
mussels, colonizing sandbanks, and eating the mussels' larvae.
"This has gone from an opportunity to resuscitate oyster
farming to a real threat for nature," says Hans van Geesbergen
of the Dutch mussels producers organization.
The deregulation of national and international markets has
reduced both the barriers to trade and surveillance, causing
more invasions, said Charles Perrings at the environment
department of the University of York in Britain.
Ships transfer approximately 3 to 5 billion tonnes of
stabilizing ballast water internationally each year -- one of
the main causes of globalization of marine species.
The U.N. International Maritime Organization (IMO)
estimates at least 7,000 different species are being carried in
ballast tanks around the world, including bacteria and other
Cholera bacteria have been discovered in ballast waters of
cargo ships and poisonous microscopic red-tide algae are
absorbed by oysters. When eaten by humans, contaminated
shellfish can cause paralysis and even death, the IMO says.
BUT CAN HUMANS SOLVE THE PROBLEM?
Once established, organisms can spread at amazing speeds.
The first Japanese crab was found in the North Sea less
than six years ago. Now they are crowding out the bigger local
shore crab and pushing north at a rate of 100 km (62 miles) per
"It breeds three to four times a year, compared with once a
year for the local crabs. I found a female with eggs in the
middle of winter," said Reindert Nijland, a crab specialist
doing a doctorate in molecular genetics at Groningen
In an attempt to tackle such a wide-ranging problem, GISIN
is drawing up a global database of invasive species.
"I think there will be a prototype global network in the
next year or so," said Michael Browne, manager of the Global
Invasive Species Database of the World Conservation Union in
Auckland, New Zealand.
"At first, it may simply integrate checklists of invasive
species from around the world so that we can see for the first
time which invasive species are where."
Building a comprehensive database of the 15,000 to 20,000
species that are known to negatively impact biodiversity from
the current online global database of 350 of the world's most
common invasive species, may take another decade.