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Aquatic Nuisance Species (ANS): Also called “aquatic invasive species (AIS)” are aquatic organisms that have been introduced into new ecosystems and cause harmful impacts on the natural resources in these ecosystems and the human use of these resources.

Aquatic Nuisance Species Task Force: An intergovernmental organization dedicated to preventing and controlling aquatic nuisance species, and implementing the Nonindigenous Aquatic Nuisance Prevention and Control Act (NANPCA) of 1990.

Bivalve: A type of mollusk with two hinged shells (e.g., clams and mussels).

Columbia River Basin: The entire region, including watersheds in Canada, which drains into the Columbia River.

Columbia River Basin (CRB) Team of the 100th Meridian Initiative: The Columbia River Basin Team has been established as part of the 100th Meridian Initiative to address the special needs of the Columbia River Basin. The CRB Team includes state, federal, Tribal, and university ANS managers and researchers.

Druse: Large colonies of young mussels that settle on older, larger zebra mussels, forming a clump.

Dreissenid: Referring to freshwater mussels in the family Dreissenidae, which includes zebra (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis).

Epilimnetic Zone: The surface water mass in a lake above the thermocline which is well mixed and therefore of uniform temperature; the surface mixed layer.

Eutrophic: High in nutrients. Water clarity is generally lower in eutrophic water bodies due to high amounts of plant growth, including phytoplankton.

Hazard Analysis and Critical Control Point (HACCP): An internationally recognized planning tool that identifies potential introduction pathways of unwanted hazards and facilitates development of associated preventative measures.

Hypolimnetic Zone: The deep water layer below the thermocline in a stratified lake.

Incident Command System (ICS): A systematic tool used for the command, control, and coordination of emergency response. ICS allows agencies to work together using common terminology and operating procedures to control personnel, facilities, equipment, and communications at a single incident scene. It facilitates a consistent response to any incident by employing a common organizational structure that can be expanded and contracted in a logical manner based on the level of required response.

Larvae: Juvenile form of certain organisms. For dreissenids, also called “veligers.”

Mitigation: Structural and non-structural measures undertaken to limit the adverse impact of natural hazards, environmental degradation and technological hazards. Examples of zebra mussel mitigation measures for industrial systems include chlorination, mechanical cleaning, and dewatering.

National Incident Management System (NIMS): A system mandated by Homeland Security Presidential Directive 5 that provides a consistent nationwide approach for governments, the private sector, and non-governmental organizations, to work effectively and efficiently together to prepare for, respond to, and recover from domestic incidents, regardless of cause, size, or complexity.

Oligotrophic: Low in nutrients. Oligotrophic water bodies have relatively few plants and algae, and tend to be very clear.

100th Meridian Initiative: A cooperative effort between state, provincial, and federal agencies and other partners to 1) prevent the spread of zebra mussels and other aquatic nuisance species (ANS) into the western United States and 2) monitor and control zebra mussels and other ANS if detected in these areas. (

Pathway: The means by which a species is transported into a geographical region or into an ecosystem. For example, recreational watercraft are one of the pathways by which zebra and quagga mussels have spread across the country.

Polymerase Chain Reaction (PCR): A method for creating millions of copies of a particular segment of DNA. PCR can be used to amplify the amount of that sequence until there are enough copies available to be detected. This technique has successfully been used in monitoring for zebra and quagga mussels.

Quagga Mussel (Dreissena rostriformis bugensis): A small freshwater bivalve mollusk that resembles the zebra mussel, but is rounder, with shells that seem asymmetrical when viewed from the front/ventral side.

Rapid Response: Immediate actions taken to contain a recently discovered invasive species before a final determination has been made that further containment or eradication is no longer feasible or warranted.

Smolt: A juvenile salmon or steelhead that has completed rearing in freshwater and migrates into the marine environment. A smolt becomes physiologically capable of balancing salt and water in the estuary and ocean waters. Smolts vary in size and age depending on the species of salmon.

Thermocline: Layer within a waterbody (e.g., a lake) where there is an abrupt change in temperature that separates the warmer surface water from the colder deep water.

Vector: See definition for Pathway.

Veliger: A larval stage of a mollusk (e.g., zebra mussel) characterized by the presence of a velum: the locomotory and feeding organ provided with cilia.

Western Regional Panel (WRP) on Aquatic Nuisance Species: A regional committee of the national ANS Task Force. Formed by a provision in the National Invasive Species Act of 1996, the WRP is comprised of western region representatives from Federal, State, and local agencies and from private environmental and commercial interests. The WRP seeks to protect limited western aquatic resources by preventing the introduction and spread of exotic nuisance species into western marine and freshwater systems though coordinated management and research activities.

 Zebra mussel (Dreissena polymorpha): The zebra mussel is a small freshwater bivalve mollusk with two matching half shells. Its name is derived from the striped pattern on its shell.

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