With worries of poisonous red fire ants originating from South America invading Japan this summer, the Mainichi Shimbun answers questions readers may have about Japanese species that have invaded other locations around the globe.
Question: Are there any plants or animals from Japan that have become a problem overseas?
Answer: Non-native species like the red fire ant that cause problems outside their native habitat are referred to as invasive alien species. In the publication "100 of the World's Worst Invasive Alien Species," created by the International Union for Conservation of Nature and Natural Resources (IUCN), the plants Japanese knotweed, kudzu (Japanese arrowroot) and wakame seaweed, along with freshwater koi carp, are among the Japanese natives listed.
Q: What kind of problems have these species caused?
A: The plants are extremely fertile and drive out whatever native vegetation or creatures are in their path. The British government is estimated to have spent over 1.5 billion pounds (roughly 230 billion yen) on eradicating Japanese knotweed. Meanwhile, carp disrupt foreign ecosystems by eating smaller fish and shellfish.
Q: How did they get there?
A: There are many cases where the plants and animals were taken by people to other countries for ornamental purposes. Japanese knotweed was taken to England in 1825, and then to North America after that, where it began to grow in the wild on both sides of the Atlantic. Japanese carp were taken abroad as Japanese gardens became popular, and fish that were eventually discarded multiplied.
Q: Did humans also take wakame abroad?
A: Wakame was spread throughout the world by spores in seawater that was used for ballast water, which weighs down and balances ships. The practice of eating wakame is absent in most cultures around the world, and the seaweed's growth has exploded in places where it has no natural predators like the sea urchin. It has caused damage such as clogging up fish-farming facilities.
Q: The ships carried the seaweed spores without knowing?
A: An international treaty regulating ballast water went into effect this September, and it requires ships that travel around the world to take measures such as installing equipment to remove organisms from the seawater used in ballasts. In addition, according to the Japan Committee for IUCN Secretary General Teppei Dohke, placing caution seals on shipped products that could possibly contain invasive alien species is also being considered.