International co-operation and improved early warning systems are essential to reduce the risk of alien invasive species, says Achim Steiner, executive director of the UN Environment Programme.
Alien species cause an estimated US$1.4 trillion worth of damage every year, says Steiner. They harm crops, poison soils, bring infections, clog waterways and oust native species.
For example, the golden apple snail, brought to Asia from Latin America in the 1980s as an aquarium pet, has become "a scourge in the paddy fields", costing the Philippines alone up to US$45 million in rice crop damage.
Alien species also challenge the Millennium Development Goals, says Steiner. In Lake Victoria, water hyacinth — a native of the Amazon basin — affects shipping, reduces fish catches, hampers electricity generation and harms human health. Controlling it costs Uganda an estimated US$112 million every year.
There are tens of thousands of alien invasive species across the world. Some countries are taking action — New Zealand, for example, implements tough customs control on foreign plants and animals, and South Africa has specific removal programmes for nature-based tourist sites.
"But far too many countries have failed to grasp the scale of the threat, or are far too casual in their response," says Steiner.
Better international co-operation, including stronger agreements under the UN's International Maritime Organization, is essential, says Steiner. He adds that developing countries must boost the capacity of their customs, quarantine and scientific institutes to improve early warning.