Combating the zebra mussel: What you need to know

Destruction of aquatic ecosystems

Zebra mussels are a freshwater mollusc that has a characteristic “D” shape and white or beige stripes. Adult mussels measure from 1 to 4.5 centimeters (cm) and can live three to five years. Their key feature is their ability to reproduce and spread, as females can lay anywhere from 40,000 to 1,000,000 eggs per year.

When it feeds, a zebra mussel can filter up to a litre of water per day, depriving other species of nutrients like chlorophyll. This filtering action also reduces densities of microorganisms like phytoplankton and zooplankton, which form the base of the food chain in lakes. The amount of food available to other organisms like young fish and invertebrates is therefore significantly reduced. As a result, the zebra mussel disrupts the entire ecosystem and can lead to a decline in many aquatic and land-based species that frequent these bodies of water. By reducing the amount of food and nutrients available, the zebra mussel creates a kind of “food desert” in which algae and bacteria proliferate, such as avian botulism, which can decimate bird populations. Furthermore, due to its substantial filtration capacity, the zebra mussel increases the transparency of the water, which fosters undesirable growth of aquatic plants and certain types of cyanobacteria, like blue-green algae, which is harmful to human health.

Economic and social impacts

Unlike native freshwater mussels, the zebra mussel has a unique ability to attach to any solid surface using filaments on its shell. It can quickly attach to watercraft, docks, and buoys, but also to dams and walls of water intake structures, which supply municipalities, industries, and private properties with water. Once attached, the mussels gather in clusters atop one another, obstructing hydraulic systems and limiting the supply of water, in addition to doing considerable damage to marine equipment and waterfront facilities.

Due to the mussels’ high density, rapid proliferation, and short life span, shells accumulate over time on beaches and lakeshores. The shells are sharp and hazardous to swimmers and also give off a strong odour due to decomposition in the masses of shells. This can result in beach closures and limit the use of watercraft, which has an impact on regional recreation and tourist activities. The decline in fish populations due to the lack of available nutrients also affects the sport fishing industry, which is highly popular among waterfront residents. Lastly, the diminished appeal of recreation and tourism can drive down residential and commercial property values and lead to higher maintenance costs for docks and marine equipment.

In short: In addition to the considerable ecological impact of zebra mussels on aquatic ecosystems, an entire sector of the economy also pays a price.

An ounce of prevention

Once the zebra mussel has entered a waterway, it is practically too late. It is nearly impossible to eradicate, dislodge, or contain the spread of this pest. Only local action and mitigation measures are usually possible. For that reason, the response relies on prevention.

Four methods of prevention and control have been developed by Quebec’s Ministère des Forêts, de la Faune et des Parcs, along with establishment of cleaning stations, to prevent aquatic invasive species from being introduced and spreading. They are:

1. Inspect the watercraft and remove any organisms that have become attached
2. Empty out and drain all water from the craft
3. Clean and dry all equipment
4. Repeat after every visit to a new waterway

Applied early, these four steps appear to have limited the spread of zebra mussels into Quebec’s waterways. This is unlike Ontario and the United States, where expansion has been very rapid. Almost all of Ontario’s susceptible water bodies have been affected in just a few years. However, despite the likelihood of the species being introduced into their waterways, a number of regions like Estrie have been spared until recently thanks to the cleaning stations that have been in place since the early 2000s.

The importance of acting quickly

To limit the ecological and economic repercussions, it is important to implement a comprehensive action plan that includes a risk assessment of introduction into the waterway and then deployment of prevention and awareness measures. A monitoring protocol must then be carefully developed to detect introduction quickly and, if necessary, develop an emergency response plan in conjunction with key stakeholders.

This is what we did with the organization Bleu Massawippi, which we have been supporting with zebra mussel efforts in Lake Massawippi in the Estrie region for a few years. After identifying a high risk of introduction in 2019, we offered training on means of early detection as part of the monitoring program for the species, which eventually led to the early discovery of zebra mussels in the fall of 2021. Since it was necessary to act quickly to introduce effective mitigation measures, we produced a scientific opinion and emergency recommendations to guide the initial steps in a coordinated action plan that mobilized lake associations, basin organizations, the scientific community, and municipal, regional, provincial, and federal authorities with the common goal of limiting the impacts in this magnificent lake in Quebec.

The key is prevention and early detection. Municipalities, residents, lake associations, and industries all have a role to play in preventing invasive species from being introduced into our waterways. Through awareness and a rigorous monitoring protocol, it will be possible to preserve waterfront infrastructure and protect aquatic ecosystems for generations to come.