Aquatic Invasive Species

What Are Aquatic Invasive Species?

Aquatic invasive species (AIS) are those that impact water bodies and wetlands. Whether they come on the trailers or hulls of recreational boats, or from the water of an angler’s bait bucket, several non-native invasive species such as New Zealand mud snails and Eurasian watermilfoil have found their way into Montana’s water bodies. Their presence can cause severe damage to local ecosystems, industry and tourism. However, Montana Fish, Wildlife and Parks is part of a strong partnership of public and private stakeholders in Montana committed to an effective strategy of prevention, containment and control. The more you know about these invaders, the more you can do to help stop the spread to Montana's precious waters.

Economic Impacts

In the United States, expenses associated with ecological damage and control of invasive species is estimated at $137 billion per year and increasing.

In Montana, some industries affected negatively by AIS include sport and commercial fishing, agriculture and raw water users – i.e. power companies and utilities. These expenses are passed on to Montana consumers –, in the form of higher water and electric bills. In 2007, Montanans and visitors spent $343 million on fishing.

Studies have shown that the presence of AIS decreases property values.

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Recreational Impacts

Photo of boat trailer with ais attached

Aquatic invasive species can also alter your recreational activities. Hunters, anglers, and even birdwatchers, among others are impacted by AIS and may find that they are no longer able to comfortably swim, or easily navigate their favorite water bodies. Also, as the habitat is modified by these invaders, the wildlife that depends on it disappears.

Fishing outings can result in disappointment when AIS modify our lake and stream habitat. Eurasian watermilfoil can clog boat motors and invasive animals such as the rusty crayfish gobble up aquatic plants like underwater lawn mowers, reducing habitat for native fish at every stage of their life cycle. The invading crayfish may even eat the eggs of our favorite sport fish.

Ecological Impacts

photo of lake, illustrating eutrophication

Humans have created conditions where plants and animals can aggressively invade and dominate natural areas and water bodies in three ways:

  1. Introducing non-native species from other regions or countries that lack natural competitors and predators to keep them in check.
  2. Disrupting the delicate balance of native ecosystems by changing environmental conditions – e.g., stream sedimentation, ditching, building roads – or by restricting or eliminating natural processes – for example building a dam. In such instances, even some native plants and animals can become invasive.
  3. Spreading aquatic invasive species through various methods – these include moving watercrafts from water body to water body without removing invasive plants and animals, and releasing bait into water bodies.

The net result is a loss in diversity of our native plants and animals as invasive species rapidly multiply and take over. About 42 percent of the species on the federal threatened or endangered species lists are at risk primarily because of invasive species.

In U.S. water bodies, the rapid spread of zebra mussels shows how profoundly an AIS can alter the environment. These tiny mussels with huge appetites for microscopic plants and animals rapidly reproduce and are capable of severely altering their environment by reducing the food supply for native organisms and by enhancing conditions for the rapid growth of blue-green algae and aquatic vegetation.

Health Impacts

Photo of foot cut from stepping on snail shells

Some invasive species may cause significant health problems. For example, a South American strain of human cholera-causing bacteria was found in ballast water tanks of ships in the port of Mobile, Alabama in 1991. Also, sharp zebra mussel shells can cut the feet of unsuspecting swimmers and waders. Zebra mussels “clean” the water by removing the phytoplankton at the base of the food chain which can then affect species higher up on the food chain including game fish. This also allows sunlight to reach higher depths which can increase unwanted plant growth.

Swimmer's Itch

Swimmer's itch is caused by the larvae of certain parasitic flatworms that can burrow into your skin while swimming. Humans are not the intended host of this parasite (waterfowl are the intended hosts) but can become an accidental host. Invasive species such as certain snails and plants can harbor the organism’s causing swimmer’s itch and therefore increasing its occurrence in infested water bodies.

Heavy Metals

Aquatic invasive species affect the amount of heavy metals in our waters in two ways. First, many aquatic invasive species (like zebra and quagga mussels) are filter feeders, meaning they filter the water for free-floating microscopic organisms to feed on. However, this process can cause accumulation of heavy metals in the tissues of filter-feeders, which can in turn lead to increased levels of heavy metals in the surrounding sediments in areas with high densities of invasive mussels. Second, anti-biofouling boat paints and coatings that are used to keep zebra and quagga mussels from attaching to boats are usually made with copper or other toxicants. The increased use of these paints has led to higher levels of copper and other heavy metals in harbors and surrounding areas.

Avian Botulism

In the Great Lakes, researchers are trying to determine if zebra mussels promote conditions for the growth of avian botulism, which have caused massive bird fatalities in the past few years, especially on Lake Michigan.