One of the largely hidden environmental problems that has been creeping up on humanity is the challenge presented by invasive alien species. In nature, each species of plant, animal and microbe has evolved as part of a community, creating for itself a niche where it could survive, while both obtaining the food and other resources that it needs, and providing food for others. Each species thus existed in balance with its own predators and prey, its diseases and parasites.
With globalization and modern forms of transportation, organisms are being transported and released all over the world, some intentionally as crops, garden plants or pets, others accidentally in packing crates, stuck to peoples' shoes or clothing, in ships' ballast water, or accompanying other desirable species. many of these do not survive in their new habitat, but some thrive and prosper, especially since the predators and diseases that used to keep their populations in balance have usually stayed behind. If the conditions are right, they can multiply uncontrollably, crowding out or consuming native species, and becoming a nuisance if not a hazard to human well-being. Controlling such invasive species can be extremely difficult and costly, and mas continue indefinitely since exterminating them is seldom an option.
There are too many examples of such biological horror stories. The Zebra Mussel has clogged the shoreline and water intakes of the Great Lakes of North America. The dangerous Fire Ant and African Bee are creeping northward in the USA. On the island of Guam in the Pacific, the brown tree snake has driven to extinction many endemic bird species and other animals. On Moorea in French Polynesia, the Giant African Snail became such a crop pest that a carnivorous snail, Euglandina, was introduced to control it. Euglandina preferred the local endemic snails and wiped out most of the native species. A South American vine is smothering and felling the native forests of Hawaii. The seaweed Caulerpa taxifolia, introduced accidentally to the Mediterranean, is crowding out the Posidonia seagrass beds that provide food and shelter for many native species. A jellyfish from America introduced into the Black Sea wiped out most of its commercial fisheries.
The costs are incalculable, the problems usually irreversible, and the consequences for the biological diversity and productivity of the planet are alarming. We could end up with a fully globalized world populated by weeds and pests. While governments are now more aware of the risks and apply appropriate quarantine measures, many people ignore these out of ignorance, selfishness or greed.
Only a combination of strict regulations, wide public education, extensive surveillance and rapid protective action can hope to reduce the dangers that invasive species represent for our future sustainability.
