One of the most destructive forces on an ecosystem is a non-native species with no natural predators or other natural controls. These species can overtake their new home in an extraordinarily short period of time by multiplying, consuming prey, and colonizing, crowding out essential local species.
An invasive species is an organism (plant, animal, fungus, or microbe) that is not only foreign to a specific area or habitat but also has negative effects on its new environment and, eventually, on our economy, our environment, or our health. Not all introduced species are invasive; the distinction is how aggressively they interact with their new surroundings.
Why we Care
Invasive species are the second greatest threat to biodiversity (the first is habitat loss). Almost half of the species at risk of extinction in the United States are endangered directly due to the introduction of non-native species alone, or because of its impact combined with other processes. In fact, introduced species are considered a greater threat to native biodiversity than pollution, harvest, and disease combined. They threaten biodiversity by (1) causing disease, (2) acting as predators or parasites, (3) acting as competitors, (4) altering habitat, or (5) hybridizing with local species.
Invasive species are costly to both society and nature by:
- Costing Americans more than $137 billion a year (Pimentel et al. 2000)
- Impacting nearly half the species listed as threatened or endangered
- Possibly devastating key industries including seafood, agriculture, timber, hydro-electricity, and recreation
- Impeding recreation such as boating, fishing, hunting, gardening, and hiking
- Spreading easily by wind, water, animals, people, equipment, and imported goods
- Increasing the frequency of localized wildfires and adversely affect watering availability
- Destabilizing soil and alter hydrology of streams, rivers, lakes, and wetlands
Washington State Invasive Species Examples
There are over 50 priority invasive species of concern in Washington State. Here are a few examples that threaten Western Washington.
Atlantic salmon (many genetically modified) are raised along the Washington and British Columbia coasts; escapes from these aquaculture operations concern fishery biologists and others working to restore native Pacific Northwest salmon runs. As of 2006, the Aquatic Nuisance Species Project states that there have been sightings of juvenile Atlantic salmon on the West Coast. The last reported sightings were on Vancouver Island in 2000.
In recent years there has been specific concern about the potential impact on wild salmon stocks from sea lice (Lepeophtheirus sp.), originating from net pens of Atlantic salmon in British Columbia. Sea lice can kill juvenile fish, even at low infestation levels.
Spartina species are aquatic grasses that grow on the mud flats and marshes of Puget Sound and our coastal estuaries. The plants tend to grow in circular clumps called ‘clones’ and are bright green. One particular species, Spartina anglica, was introduced either in shipments of oysters from the East Coast or as packing material in ships’ cargo. It creates large monocultures that outcompete native plant species for space, including rare and endangered plant species, reducing marsh biodiversity and ecological functions.
European Green Crab
The European green crab is a small shore crab that is not necessarily green like its name implies. It typically is found in high intertidal areas and marshes in coastal estuaries and wave-protected embayments, and can live on a variety of surfaces including sand, mudflats, shells, cobble, algae, and rock. It is an opportunistic feeder and aggressive invader. It is native to the eastern Atlantic from Norway to North Africa.
The European green crab is a ravenous predator that eats small crustaceans and many other plants and animals, and can have dramatic negative impacts to native shore crab, clam, and oyster populations. First introduced to the East Coast of the US, green crabs are believed to have caused the collapse of the soft-shell clam industry in New England; their digging habits also have slowed eelgrass restoration efforts. One green crab can consume 40 half-inch clams a day, as well as other crabs its own size. On the West Coast, green crabs were introduced to San Francisco Bay either via ballast water or through the lobster trade. Further invasion north is facilitated by strong advective currents that are associated with El Nino events. The 1998 event brought crabs as far north as Vancouver Island; luckily populations have not established yet. This year’s El Nino may prove strong enough to bring crab larvae into Puget Sound and British Columbia again. How severe the invasion will be, only time will tell.
Scotch broom (Cytisus scoparius) is an upright shrub with yellow flowers in the pea family. It grows primarily in open, dry meadows and along roads. It is an aggressive early colonizer and typically shows up in recently disturbed areas. A European native, scotch broom crowds out native species and negatively impacts wildlife habitat by creating vast monocultures. It can form dense, impenetrable stands that displace farmland and/or prevent native species from colonizing. Scotch broom also produces toxic compounds, which in large amounts can cause mild poisoning in animals such as horses.
Coming up: in Part II, we will discuss how invasions happen and what can be done to stop them.
For more information, contact Jason Stutes at firstname.lastname@example.org.
References: Pimentel, D., Lach, L., Zuniga, R., Morrison, D., 2000. Environmental and economic costs associated with non-indigenous species in the United States. BioScience 50 (1), 53–65.