We’ve learned about invasive zebra and quagga mussels in the biosphere before (see Zebra and Quagga Mussels: Georgian Bay’s Filter-Feeding Invaders). Now the question is, what is being done to control them?
Zebra and quagga mussels belong to the genus Dreissena and are collectively referred to as Dreissenids. While they first arrived in the Great Lakes modestly in 1988 via ship ballast waters, they now coat the bottom of the Great Lakes (with the exception of Lake Superior) and many inland lakes. Along with the considerable damage they cause to aquatic ecosystems, they can clog drainpipes, water intake pipes, and water systems of power plants and industrial facilities.
Governments, research scientists, and the private sector throughout North America are investigating diverse strategies to help manage and control the razor-sharp zebra and quagga mussels. While there is no silver bullet for the Dreissenid mussel problem, progress has been made in some locations. In this month’s blog post, we take a look at some of the control strategies currently being researched and tested.
Picking Them Off, One by One
Researchers have achieved some success in reducing the number of mussels in a specific area or on a particular surface by manually removing live mussels and dead shells, and properly disposing of them. Workers and divers scrape them off surfaces with paint scrapers, screwdrivers, chisels, and knives, then use suction devices to vacuum everything into collection bags.
In 2000, divers removed more than 19,000 juvenile and adult zebra mussels by hand from Lake George, New York. Their labour-intensive efforts have been successful to this day.
Hydro-blasting with high-pressure water guns is another option to get mussels off hard surfaces. However, this technique is only effective if the detached mussels are killed or removed, not simply relocated.
Large, dark tarps, known as benthic mats, are anchored onto lake bottoms over top of Dreissenids. These mats are a type of physical control and restrict the water flow and oxygen getting to mussels. They also prevent photosynthesis from taking place under the mat, a process necessary for the growth of the Dreissenids’ food source, phytoplankton. In some cases, chemicals that kill mussels can be introduced under the tarp to increase its efficacy.
Recently, researchers placed a several hundred square metre tarp, weighed down with heavy chains, at the bottom of Lake Michigan. Within a month-and-a-half, all the mussels under the tarp were dead. So far, none have come back. Over the next three years, they plan to try this out on a two-and-a-half-acre plot in deeper waters near Milwaukee, where the mussels are bigger and the population is denser.
The same research team is also looking at testing a heavy, mussel-crushing roller that would move along the lake bottom.
Dewatering / Drawdown
In the United States, some agencies have attempted removing enough water in the winter from invaded lakes to starve or freeze mussels to death. In 2010, a successful winter water drawdown was conducted on Lake Zorinsky in Nebraska. Zebra mussels were eradicated and the lake was refilled and re-opened for recreation in 2012. Unfortunately, zebra mussel larvae were detected in the lake again more recently.
A common component of fertilizers, potassium chloride or potash, kills mussels by harming their respiratory systems. When used properly, potash does not negatively affect native fish or plants in the surrounding ecosystem. In North America, potash is currently used to manage mussel populations in closed cold and hot water systems, as well as in open waters with limited inflow and outflow, such as reservoirs and quarries.
In 2006, potash was used to eradicate zebra mussels at Millbrook Quarry, Virginia. Seven years later, when the first mussel was reported in Lake Winnipeg, Canadian officials contacted the company that had worked on the Millbrook Quarry for advice on how to proceed. The four affected Lake Winnipeg harbours were closed off with silt curtains between May and June 2014, and potash was pumped in. When additional mussels were found, including in open waters, officials ramped up the watercraft inspection program and continued containment and dosing in affected areas. The battle against zebra mussels in Lake Winnipeg continues today with efforts primarily focused in the south basin.
The active ingredient in the biopesticide Zequanox® is dead bacterial cells that destroy the digestive lining of mussels. Zequanox® is approved in the U.S. for use in open waters. It has been used throughout the United States Great Lakes region and in inland lakes elsewhere.
In 2019, the Invasive Mussel Collaborative coordinated a demonstration control project using Zequanox® at Good Harbour Reef in Lake Michigan. The biopesticide was pumped under tarps anchored directly to the reef over a three-day period. The result was Dreissenid mortality rates of up to 97%. Research continues on the use of Zequanox® in different settings, including in open waters.
For decades hydroelectric stations such as those at Niagara Falls, as well as water filtration plants, have been using low concentrations of liquid chlorine and/or sodium chloride to kill Dressenids in their intake/outflow pipes and mechanical equipment. Chlorine is toxic to mussels at all stages of their reproductive cycle. Chlorine concentration is an important consideration with this control method as chlorine can have adverse affects on water quality and aquatic life.
Niclosamide is a compound currently in use to control invasive sea lamprey and freshwater snails, and is also toxic to mussels. It is currently being tested in the U.S for use in early detection and rapid response activities.
Commercially available copper compounds vary in their elemental makeup, but all are toxic when ingested by mussels. A variety of these compounds have been used to treat lakes in the U.S. in the past.
Introducing an invasive species’ predator to a system which is already stressed from invasion is known to be risky. Biological controls run the risk of causing further harm to the ecosystem rather than helping. However, there have been instances where biological controls have been successful and studies are underway in the western United States focusing on the possibility of utilizing redear sunfish (native to that region), a mollusk, and a snail, as biological controls for Dreissenids.
What You Can Do
Clean, Drain, Dry
Effective January 1st, 2022, Ontario’s Invasive Species Act now regulates watercrafts (boats, canoes, and kayaks) as carriers of invasive species.
This means you are now required by law to take reasonable precautions to remove all aquatic plants, animals, and algae from your boats, boat equipment, vehicles, and trailers before putting it in any body of water.
This also means you are now required by law to clean your boat and boat equipment properly when you move your boat overland. You must, for instance, remove or open the drain plugs so water can fully drain out (unless it is a drainpipe for a drinking water system, marine sanitary system, or closed engine cooling system).
To keep your boat mussel-free:
- Clean your boat and equipment—away from storm drains or waterways.
- Drain your watercraft of any water it picked up from your trip, including ballasts, bait buckets, bilges, and internal compartments that could hold onto water.
- Dry everything thoroughly.
Detailed information on exactly how to clean, drain, and dry your boat can be found here: Boaters Action Plan.
Moss Ball Products and Aquarium Water
Dreissenid mussels have recently been found in moss ball products, an aquarium plant product made of green algae. Do not flush these products or aquarium water down the toilet, pour them down the drain or throw them in your compost. Treat and dispose of them properly to eliminate the potential for Dreissenid mussels to be introduced into local waterbodies. Detailed information on how to dispose of aquarium moss balls and water is available from Fisheries and Oceans Canada here.
If you spot Dreissenid mussels in a new location or in a moss ball product, contact Ontario’s invasive species hotline, 1-800-563-7711, Ontario’s Early Detection and Distribution Mapping System, and/or Ontario’s Invading Species Awareness Program.
To learn more about ongoing Dreissenid control research, readers are directed to the Invasive Mussel Collaborative.
Helen Kohl is a retired journalist and writer who is lucky enough to live in the Georgian Bay Biosphere region.