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History of Mussel Introductions and Management Responses

Referred to collectively as dreissenid mussels, zebra and quagga mussels are closely related freshwater mussels in the genus Dreissena each with a slightly different invasion history and timeline. The discovery and subsequent spread of both species of dreissenid mussels heralded a sea change in aquatic invasive species policy and management in the United States. For much of their initial invasion history in North America, however, the zebra mussel, Dreissena polymorpha, was the primary species of concern and many policy and outreach documents from the first 20 years of the invasion focus specifically on the zebra mussel.

The zebra mussel, believed to have been transported from Europe via ballast water in the mid-1980s, was first discovered in Lake St. Clair in June 1988 and soon after found to be established throughout the Great Lakes. Over the next year, extensive colonies of mussels, numbering in the tens of thousands per square meter, were reported from Lake Erie. In late 1989, zebra mussels were found in the intake pipes of power production, water treatment and other industrial facilities located on Lake Erie as well as the Detroit River (O’Neill and Dextrase 1994).

These unprecedented impacts and rapid colonization of a non-native species in the Great Lakes provided the primary impetus for the passage of the Nonindigenous Aquatic Nuisance Prevention and Control Act (Act, 16 U.S.C. 4701-4741) in 1990. The Act included a Zebra Mussel Program to ensure emphasis on what was then the immediate problem: the need for coordination among the US and Canadian governments, federal agencies, and other entities to address the zebra mussel infestation and to develop and disseminate information on mussel control options (ANSTF 1994).

In adopting the Act, Congress focused on zebra mussels and the growing concern that they would spread beyond the Great Lakes as well as a broader mandate for prevention, control, and management of invasive aquatic species. The Act created an intergovernmental mechanism for the development of a cooperative national program, known as the Aquatic Nuisance Species Task Force (ANSTF). Other requirements of the Act included the listing of the zebra mussel as an injurious species under the Lacey Act, the creation of ballast water and shipping initiatives to prevent new introductions, and the development of a State Aquatic Nuisance Species Management Plan and Grant program (ANSTF 1994). The ANSTF established the Great Lakes Panel on Nonindigenous Species, the first regional aquatic nuisance species panel, with the acknowledgement that as zebra mussels spread so would the need to address ANS issues and problems.

The first reported foray of the zebra mussel beyond the Great Lakes came in 1991 when the mussel moved through the Erie Canal into the Hudson River (O’Neill and Dextrase, 1994). By 1992, the zebra mussel had spread beyond the Great Lakes Basin and into the inland waters of the US and Canada. Part of this range expansion was likely facilitated by downstream dispersal of larvae via Chicago Sanitary and Shipping Canal (Illinois) and Trent-Severn Waterway (Ontario) into connected waterways, as well as by mussel-fouled commercial barges moving populations upstream from these interconnected waterways. By 1993, the appearance of zebra mussels in waterbodies not directly connected to infested waters lent credence to the implication that recreational boaters and anglers were playing a role in the spread of mussels.

In the meantime, the quagga mussel, Dreissena rostriformis bugensis, arrived in North America - likely via the same pathway as the zebra mussel. Discovered in 1989 in Lake Erie and given the common name quagga mussel (the quagga being an extinct subspecies of African plains zebra), the taxonomy of this second dreissenid mussel was less certain. It wasn't until 1991 that researchers settled on the currently accepted nomenclature (Nalepa 2010). With little fanfare, the quagga mussel proceeded to spread throughout the Great Lakes in the 1990s, although it wasn't until 2005 that it was found in Lake Superior. In the mid-1990s quagga mussels had spread into the upper Ohio and Mississippi Rivers (Nalepa 2010) but the zebra mussel remained the “poster-child” of the aquatic nuisance species management world.

In 1996, the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990, was reauthorized and amended by the National Invasive Species Act (Act, PL 104-332). Among other policies, the reauthorization provided for the expansion of the state ANS management plan and grant program to include interstate management plans and allow tribal participation in addition to states (NISA 1996). The Act also required the ANSTF to encourage the development and use of regional coordination panels in areas beyond the Great Lakes (NISA 1996).

In 1997, in recognition of the threat of mussels to western aquatic ecosystems as well as public and private water delivery systems, the Western Regional Panel on Aquatic Nuisance Species (WRP) was formed under a provision in the newly reauthorized Act (WRP 2019). One of the early accomplishments of the WRP was the development of an action plan to prevent the spread of zebra mussels and other aquatic nuisance species west of the Mississippi River Basin. With the approval of the ANSTF, that plan became the 100th Meridian Initiative: A Strategic Approach to Prevent the Westward Spread of Zebra Mussels and Other Aquatic Nuisance Species (USFWS 1997). At the time of its launch, the most westward population of zebra mussels was located in Oklahoma but, without a coordinated prevention effort in place, the threat to the West seemed imminent.

The goals of the 100th Meridian Initiative are to: 1) prevent the spread of zebra mussels and other ANS in the 100th meridian jurisdictions and west and 2) monitor and control zebra mussels and other ANS if detected in these areas. These goals will be achieved by addressing seven components: 1) information and education, 2) voluntary boat inspections and boater surveys, 3) commercially hauled boats, 4) monitoring, 5) rapid response, 6) identification and risk assessment of additional pathways, and 7) evaluation.


Upon approval of the 100th Meridian Initiative by the ANSTF, federal grant funding became available to support implementation of activities that fit the goals of the 100th Meridian Initiative. Funding has included grant support for River Basin Teams such as the Columbia River, Missouri River, etc.

In January 2007, quagga mussels were detected in the Boulder Basin of Lake Mead, a reservoir on the lower Colorado River. This was the first confirmed establishment of any dreissenid mussel in the West and a huge jump for the quagga, known prior to only the Great Lakes region. Within a few weeks of the initial discovery, divers confirmed quagga mussels 150 miles downriver on the intakes grates of the Colorado River Aquaduct; the connectivity of the lower Colorado River Basin to both drinking and irrigation water diversions had facilitated the rapid downstream spread of quagga mussels into Southern Nevada, Arizona, and Southern California (USBR 2008). In early 2008, zebra mussels were discovered in San Justo Reservoir, California (USBR 2019). The sparsely used Bureau of Reclamation reservoir was quickly closed to the public and zebra mussels do not appear to have been spread from this location. In the meantime, zebra mussels have continued to spread throughout the Missouri River basin states.

While the 100th Meridian Initiative effort is considered to have been effective in enhancing early detection capacities and reducing the risk of introductions of mussels in the West, with the arrival of quagga mussel in the Lower Colorado River, the focus of the Western states expanded to include rapid response and other contingency planning efforts.

Seeing an immediate need for coordinated and extensive action to prevent the further spread and establishment of quagga mussels in the West, the membership of the WRP developed the Quagga-Zebra Mussel Action Plan for Western U.S. Waters (QZAP). The goal of this document was to summarize current strategies to address the invasion of zebra and quagga mussels in the West, and to identify and prioritize the specific actions needed to comprehensively prevent the further spread of these mussels, respond to new infestations, and manage existing infestations (QZAP 2010).

In 2012, sensing the need to intentionally expand the coordination of the Western States to tackle legislative and legal challenges to prevention efforts including watercraft inspection and detection efforts, the WRP formed a Building Consensus in The West Committee. Building Consensus represented a unique approach in the realm of aquatic invasive species management in that it brought together federal and state invasive species program managers, law enforcement officers, Assistant Attorneys General and boating industry representatives. The goal was to develop an effective and proactive approach to AIS prevention while increasing consistency in messaging and boater experiences (Building Consensus 2019). Much of the work was funded by the U.S. Fish and Wildlife Service with AIS Prevention & Control Funding (formerly known as 100th Meridian Initiative funding). The initial process included:

…increased economies and efficiencies for agencies administering watercraft inspection and decontamination programs, consistencies in messaging and experiences for recreational boaters, and standard protocols and definitions for waterbody classification, monitoring and regulations among western states.

Recognizing that even the most effective prevention programs may not stop the transport and introduction of dreissenid mussels, early detection and rapid response has taken on a critical role in dreissenid management in the Pacific Northwest (the last remaining uninfested region in the Western US).

Coordinated detection and monitoring efforts increase the likelihood that:

  • Potential threats are identified in time to allow for timely management responses, and 

  • New dreissenid mussel populations are detected in time to allow the most cost effective and environmentally sound management actions.

Rapid response planning efforts increase the likelihood that:

  • Support resources for response actions exist prior to action; 

  • Responses to invasions rely on best available science and lessons learned from previous efforts;

  • Managers understand the legal and conservation concerns relevant to each response scenario; and 

  • Adequate and timely information is provided to decision-makers, and intentional and inclusive stakeholder engagement is achieved prior to response initiation.

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