A species that is not indigenous to its ecosystem and whose introduction may cause harm to native species and human health is termed invasive. Often not thought of as 'invasive' at the time of introduction, these species make their way into new ecosystems both intentionally-exotic pets, hybridization, food, pest control, landscape ornamentals-and accidentally such as 'stowaways' that attach themselves to shipping ballast tanks, shipping crates, travelers, or become mixed into seed purchased from other countries. While 90 percent of immigrant species cause little to no detectable damage to their new homes, a small number do wreak havoc, often crippling ecosystems by preying on local species or competing for limited resources (according to Mongabay.com). Eco-destruction takes place on land and in the sea, with fauna and floral, and with insects and microbes. The ability to control these invaders and decrease their rate of introduction is progressing.
Free from their natural predators, these organisms can establish a stronghold while thriving in habitats with low biodiversity. Invaders have a knack for filling previously unoccupied niches, and often out-compete, or simply eradicate, native species. In addition, they often bring diseases that wipe out native animals, as exemplified by the New Zealand mud snail that turned up in the Snake River, which runs through Montana and Idaho. Not only was the mud snail better at gobbling up resources than the native mollusks-so that many of the species began to die out-but it proved a lousy food source for fish. From the ballast water of transatlantic vessels came the inadvertent introduction of the zebra mussel to Lake St. Claire, the waterway connecting Lake Huron and Lake Erie. Wildly adaptable to a wide range of environments, this Asian mussel soon made itself at home, causing a decline in native species, a reduction in food and oxygen for native fauna, and decreasing water quality. It also caused over $100M in damage to clogged water pipes and filtration systems, so much so that household water flow reduced to a trickle. The examples of invasive species are endless and include crustaceans, amphibians, reptiles, fish, birds, and mammals. According to the H.A. Mooney and E.E. Cleland of the National Academy of Sciences, often the invasive species mate with native species creating a new hybridized species that can cause a loss of fitness in native species and even a threat of extinction.
Perhaps more disturbingly, James T. Carlton notes in his report on Introduced Species (see hyperlink below) for The Pew Oceans Commission: "Every assessment indicates that the rate of marine introductions in U.S. waters has increased exponentially over the past 200 years and there are no signs that these introductions are leveling off. New introductions are occurring regularly on all coasts, producing immediate and damaging impacts, and leading to millions of dollars in expenditures for research, control, and management efforts. In the San Francisco Bay alone, for example, an average of one new introduction was established every 14 weeks between 1961 and 1995."
Can steps be taken to curb invasive species? On a national level, the National Oceanic and Atmospheric Administration has initiated an Alien Species Early Detection and Warning System, which detects the early presence of invasive species in a given region, quantifies the possible risk to the ecosystem, and warns managers before the species can spread to the point of invasion. The Department of Agriculture has implemented numerous measures that encompass research, prevention, monitoring, and restoration. For more information, visit their website listed below. States too have taken action: for instance, California has enacted legislation that, amongst other things, mandates the cleaning of ballast tanks, propellers and hulls of any ship prior to entering its harbors; and Michigan has taken similar measures to protect the Great Lakes.
Individuals can also help control invasive species and allow local plants and animals to thrive. Boaters must be aware that the water transported in their ballast may contain non-native species, and therefore they should empty ballast water in the same areas where originally collected, assuming it is clean enough for pump out without the need for treatment. After boating, owners should carefully clean the boat's hull and propellers before introducing the vessel to a new area, and wash down their vehicle and tires after transporting trailers to avoid hauling invasive species to different eco-regions. Finally, never release aquarium contents into local waterways. These simple first steps can make great strides in protecting natural eco-systems and avoiding the extinction of native species.
National Oceanic and Atmospheric Administration:
United States Department of Agriculture:
Introduced Species in U.S. Coastal Waters: