TRAVEL AND TRADE: Hidden Threats.

• Author: FRENCH, HILARY
• Position: Global ecological disruptions, spread of epidemics and infectious diseases - Statistical Data Included

FOR MOST OF HISTORY, natural boundaries such as mountains, deserts, and ocean currents have served to isolate ecosystems and many of the species they contain. However, these physical barricades are now becoming permeable as people and organisms spread around the globe, leading to ecological disruptions with damaging and unpredictable consequences.

Ecological integration has accelerated dramatically in recent decades, as trade and travel have skyrocketed. More than 5,000,000,000 tons of goods are being shipped across the world's oceans and other waterways annually. International air travel is also soaring. More people are flying greater distances than ever before, with 2,000,000 crossing an international border every day. Since 1950, the number of passenger-miles flown has increased at an average of nine percent.

The rapid growth in the movement of human beings and their goods and services around the world has provided convenient transportation for thousands of other species of plants and animals that are taking root on foreign shores. This explosion in the movement of species and microbes across international borders poses a major threat to both the planet's biological diversity and the health of its human inhabitants.

The world community is just beginning to awaken to the pervasive danger posed by the spread of non-native "exotic" species, a process dubbed bioinvasion. Once exotics establish a beachhead in a given ecosystem, they often proliferate, suppressing native species, Invasive species are a major threat to the diversity of life on Earth. Nearly 20% of the world's endangered vertebrate species are threatened by exotics, and almost half of all species in danger of extinction in the U.S. are imperiled at least in part by non-native species.

Ballast water from international shipping is a major culprit in the spread of aquatic species. On any given day, some 3-10,000 of them are moving around the world in ship ballasts. When the ballast water is discharged, so are the organisms, after which they often cause incalculable damage. For example, a ballast water-induced invasion of the Black Sea by the Atlantic jellyfish in the early 1980s was instrumental in the collapse of the fisheries there by the end of that decade.

The U.S. Great Lakes have been hard hit by bioinvasions over the last several decades. One villain is the zebra mussel, which probably originated in the Caspian Sea and was likely first released into the Great Lakes from a ship's ballast water tank in the mid 1980s. Zebra mussels have spread widely throughout the lakes and other waterways of eastern North America, where they have wreaked havoc with delicate ecological systems by ingesting large quantities of algae--a fundamental component of aquatic food webs. Zebra mussels also multiply rapidly, clogging water intake pipes and encrusting aquatic infrastructure and boats. The associated economic losses are expected to add up to a cumulative figure of at least $3,000,000,000 within the next few years.

Terrestrial ecosystems are no less at risk. The damage wrought by the pesticide-resistant whitefly is a warning of the high stakes involved. The whitefly caused tens of billions of dollars of agricultural damage in California in the early 1990s before moving on to South America, where it has helped spread crop viruses that led to the abandonment of more than 1,000,000 hectares of cropland. (A hectare equals 2.47 acres.)

In the U.S., the aggressive purple loose-strife plant has become a widely known symbol of the broader threat. It is thought to have first been accidentally introduced into North America in the late 18th century in wool imports and solid ship ballast, then deliberately imported for ornamental and likely for medicinal purposes during...