Subject of Possible Rule Making: Chapter 16-470 WAC, Quarantine—Agricultural pests. The department is considering establishing a quarantine on Dreissenid mussels, specifically zebra and quagga mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) as harmful plant pests and regulating the import of Aegagropila linnaei (common product Marimo moss balls), in order to prevent the introduction of Dreissenid mussels to Washington state.

Reasons Why Rules on this Subject may be Needed and What They Might Accomplish: In March 2021 invasive zebra mussels were found attached to moss balls that were for sale at a pet store in Washington state. Detections began occurring in other states, such as neighboring Oregon, as well as Canada. Zebra mussels are fingernail-sized freshwater mollusks that are native to Eastern Europe. These mussels are known to reach extremely high densities outside of their native habitat and can quickly take over a body of water once they become established, smothering native species. Quagga mussels are closely related to zebra mussels and can have a similar harmful impact on the environment.

In an established population, Dreissenid mussels can cause severe environmental and economic damage. This includes disrupting food systems in bodies of water by filtering out algae and other microscopic biomass that native species need for food. Dreissenid mussels will also incapacitate native species of mussels by attaching to them. Established populations of this pest can change water chemistry, which can lead to increased blue green algae outbreaks and unpalatable water. All of this could lead to grievous impacts to Washington's aquaculture industry.

Additionally, Dreissenid mussels can indirectly injure or cause damage to plants and field crops, by disrupting water delivery, through agricultural irrigation systems. Established populations of Dreissenid mussels can clog ditches and irrigation pipes, disrupting the flow of water and causing water stress and crop damage. Restoring clogged irrigation systems can be extremely costly to fix. Regulating the import of Aegagropila linnaei, which have been found to carry this plant pest, will prevent the spread of Dreissenid mussels in the state and protect Washington's agricultural industry.

Aegagropila linnaei are bought and sold for use in aquariums. They are composed of a green filamentous algae species. In nature Aegagropila linnaei have been known to provide habitat for fish, shrimp, and other species. They are sold all over the United States by national retail chains, as well as smaller retailers and online suppliers. Although Aegagropila linnaei themselves are not invasive, they are a known carrier for Dreissenid mussels and other potentially invasive species. By designating Aegagropila linnaei as a regulated article, the department is breaking a known pathway for the movement of Dreissenid mussels into the state.

Other Federal and State Agencies that Regulate this Subject and the Process Coordinating the Rule with These Agencies: United States Department of Agriculture and Washington department of fish and wildlife. The department is engaging in ongoing communications about Dreissenid mussel control and the quarantine of plant conveyances such as Aegagropila linnaei, through regular meetings of the Washington invasive species council.

Interested parties can participate in the decision to adopt the new rule and formulation of the proposed rule before publication by contacting Brad White, Assistant Director, Plant Protection Division, Washington State Department of Agriculture, P.O. Box 42560, Olympia, WA 98504-2560, phone 360-902-1907, fax 360-902-2094, TTY 800-833-6388 or 711, email bwhite@agr.wa.gov, website https://agr.wa.gov/services/rulemaking; or Cindy Cooper, Plant Services Program Manager, Plant Protection Division, Washington State Department of Agriculture, P.O. Box 42560, Olympia, WA 98504-2560, phone 360-902-2062, fax 360-902-2094, TTY 800-833-6388 or 711, email CCooper@agr.wa.gov, website https://agr.wa.gov/services/rulemaking.