Zebra mussels (Dreissena polymorpha) are freshwater mollusks, fingernail-sized, identifiable by their D-shaped shells and often striped patterns. Originating from the Caspian and Black Seas in Eurasia, these organisms were introduced to North America in the 1980s via the ballast water of transatlantic ships. Since their arrival, they have rapidly spread across various freshwater systems, including the Great Lakes and major river basins.
Their ability to reproduce quickly and attach firmly to surfaces poses significant ecological and economic threats. A single female zebra mussel can produce hundreds of thousands to over a million eggs per year, leading to dense populations that can exceed 700,000 individuals per square meter. They adhere to almost any submerged hard surface using strong byssal threads, causing extensive biofouling. This rapid proliferation and attachment disrupt aquatic ecosystems by outcompeting native species for food and space, and they cause substantial damage to infrastructure by clogging pipes and water intake systems.
Preventing Future Infestations
Preventing the spread of zebra mussels is important, as established populations are difficult to remove. A widely adopted and effective method for individuals is the “Clean, Drain, Dry” protocol, particularly for watercraft and associated gear. This three-step process reduces the risk of transporting these invasive organisms between water bodies.
The first step, “Clean,” involves inspecting all watercraft, trailers, and equipment for visible aquatic plants, animals, or mud. This includes the hull, propeller, anchor, and fishing gear. Any discovered organisms or debris should be removed and disposed of in a trash receptacle or on dry land, away from any water source.
Following cleaning, the “Drain” step requires removing all water from the boat and equipment. This means opening all drain plugs, emptying bilges, livewells, bait buckets, and engine cooling systems. Microscopic zebra mussel larvae, known as veligers, can survive in small amounts of standing water, making draining necessary.
The final important step is “Dry.” All equipment should be allowed to dry for a period before being used in another body of water. Adult zebra mussels can survive out of water for several days, and in some conditions, up to 30 days. A drying period of at least five days is recommended to ensure any remaining veligers or adult mussels die.
Removing Mussels from Personal Watercraft and Gear
When zebra mussels have already attached to personal watercraft or gear, several methods can be employed for their removal. Manual scraping is an approach using tools like stiff brushes or scrapers to dislodge the mussels from hard surfaces. This method is suitable for hulls, trailers, and other non-delicate equipment, but avoid damaging the surface material.
Pressure washing offers an efficient way to remove mussels from larger areas. High-pressure water streams can dislodge mussels and their byssal threads from boat hulls and trailers. For effectiveness, hot water treatment is useful, as zebra mussels are sensitive to high temperatures. Water heated to at least 140°F (60°C) applied for a minimum of 10 seconds can kill both adult mussels and their larvae.
Extended air drying is another effective method for portable gear. If watercraft or equipment can be kept out of the water for several days to weeks, any attached mussels will desiccate and die. The duration required depends on environmental conditions, with warmer, drier conditions accelerating the process. All removed mussels and debris should be disposed of in sealed bags in the trash.
Controlling Mussels in Docks and Small Structures
Managing zebra mussel infestations on stationary structures like docks, boat lifts, and swim platforms requires strategies. Seasonal removal of these structures from the water, allowing them to dry completely over the winter months, is an effective control measure. This prolonged exposure to air and freezing temperatures will kill attached mussels.
For structures that cannot be easily removed, manual scraping remains an option. Regular inspection and scraping of submerged surfaces can help keep mussel populations in check. Specialized tools designed for underwater scraping can improve efficiency.
Covering or smothering techniques can also be effective for smaller, fixed structures. This involves draping tarps or plastic sheeting over the infested sections of the structure, securing them to deprive the mussels of light and oxygen. This method can suffocate mussels over several weeks. Hot water or steam treatments can also be applied to submerged parts of docks and lifts, using similar temperature guidelines as for watercraft to kill the mussels. Consult local regulations before undertaking any control methods that might impact water quality.
Professional and Large-Scale Eradication
When zebra mussel infestations are large or affect large bodies of water and infrastructure, professional intervention becomes necessary. Individual efforts are insufficient for these large-scale challenges. Specialized professionals and agencies employ a range of advanced control methods that require specific expertise and often permits.
Chemical treatments involve the application of molluscicides, substances designed to kill mollusks. Potassium chloride, for example, can be used in targeted applications to control mussel populations within enclosed systems. Biological control methods, while still experimental, explore the use of fish species that prey on zebra mussels or pathogens that can affect their populations.
Physical methods are also utilized in large-scale eradication efforts. Dewatering, which involves removing water from an infested area, is effective in contained environments. Oxygen deprivation techniques, such as sealing off sections of water to reduce oxygen levels, can suffocate mussels. Specialized filtration systems are employed in water treatment plants to prevent veligers from entering and establishing colonies within pipes. These methods are implemented by trained personnel due to their complexity, potential environmental impacts, and regulatory requirements.