About UNEP UNEP Offices News Centre Publications Events Awards Milestones UNEP Store
GEO-3: GLOBAL ENVIRONMENT OUTLOOK  
UNEP Website GEO Home Page

Bio-invasion

Bio-invasion is now thought to be the second gravest threat to biodiversity in North America, after habitat destruction and degradation (CEC 2000). Competition or predation by non-native species imperils nearly half of the species listed as threatened or endangered under the US Endangered Species Act (Wilcove and others 1998). In Canada, alien species have been involved in causing risk to about 25 per cent of endangered, 31 per cent of threatened and 16 per cent of vulnerable species (Lee 2001).

Restoration of the Florida Everglades

The Everglades is the central part of a 23 000 km2 watershed covering the lower third of Florida. In the early 1900s, large tracts were drained and water supplies reconfigured. Protected from flooding by levees and canals, South Florida became home to six million people along the Miami-Palm Beach corridor and an important sugarcane, fruit and vegetable producer (UNDP, UNEP, World Bank and WRI 2000).

Originally stretching over 11 650 km2, nearly half of the Everglades wetlands have been lost, reducing the amount of freshwater flowing to the coast, disrupting salinity levels and altering the natural capacity of the ecosystem to store and release water. The state of the Everglades deteriorated most rapidly over the past two decades with sea grass die-offs, the invasion of non-native species, nutrient contamination, large algal blooms in Florida Bay and declines in fishing harvests and some bird populations (UNDP, UNEP, World Bank and WRI 2000).

Regional efforts to address the problems began in the early 1980s but it took until 1998 for all parties - the sugar industry, environmentalists, real estate developers and American Indian tribes - to come together in support of a comprehensive plan to restore and preserve the Everglades. Developed by the Army Corps of Engineers, it is the world's most ambitious and extensive wetlands restoration effort, costing the federal government US$7.8 billion. It will take more than 20 years to complete (Alvarez 2000, Army Corps of Engineers 2000).

Invasive aquatic species are particularly threatening to wetland and freshwater ecosystems (see box below) and can also pose serious health risks. For example, human cholera bacteria were found in ballast tanks and in oyster and fin-fish samples in Mobile, Alabama, in 1991 (ANS 2000). Alien aquatic species are expected to contribute to the extinction of native freshwater species in North America at a rate of 4 per cent a decade over the next century (Ricciardi and Rasmussen 1999).

Bio-invasion

Bio-invasion is the influx of alien invasive species. Alien species are considered invasive when they become established in natural habitats, are agents of change, and threaten native biological diversity. Alien invasive species include bacteria, viruses, fungi, insects, molluscs, plants, fish, mammals and birds (IUCN 2001).

Species that become invasive can be introduced either intentionally or unintentionally through pathways (or vectors). These include transportation (by water, land and air; in the goods themselves, in dunnage, packing materials or containers, in or on ships, planes, trains, trucks or cars); agriculture; horticulture and plant nursery stock; aquaculture industry; live food fish industry; bait fish; ornamental pond, water garden and the aquarium pet trades. Where there are no natural predators, they can come to dominate ecosystems, and can alter the composition and structure of food webs, nutrient cycles, fire cycles, and hydrology and energy budgets, threatening agricultural productivity and other industries dependent on living resources (Alonso and others 2001).

As an example, purple loosestrife (Lythrum salicaria), which was introduced from Europe in the mid-1800s as a garden ornamental, has been spreading in North America at a rate of 115 000 ha a year, invading wetland habitats where it dominates native plants and deprives waterfowl and other species of food sources (Haber 1996, Pimentel and others 1999). When non-indigenous aquatic weeds such as purple loosestrife, Eurasian water milfoil and hydrilla replace native species, they establish dense colonies that can impair navigation, water-based recreation and flood control; degrade water quality and wildlife habitat; accelerate the filling of lakes and reservoirs; and depress property values (Haber 1996).

The high economic costs of damage caused by bioinvasions in North America is causing increasing concern. Both countries have developed monitoring plans and information systems to help control bioinvasion (Haber 1996, Kaiser 1999).

Responses to the challenge of invasive species include legislation, policies, and plans and programmes that focus on preventing the invasion of new species and the eradication or control of established ones. Canada and the United States cooperate in programmes related to invasive species in the Great Lakes, for example. Despite requirements for ships to exchange ballast water at sea, however, the influx of new species into the Great Lakes continues and is considered to be a serious threat to the integrity of the Great Lakes ecosystem.

As trade increases, new invasions are expected. In addition, it may be that global climate change could create conditions that are even more conducive to bioinvasion (Holmes 1998). North American as well as global cooperation is essential to stem the tide of bioinvasion and the damage it causes.