Zebra Mussel Questions and Answers

- May 2017

What are zebra mussels?

Adult zebra mussels are small freshwater mollusks (clams) named for their typical striped pattern on their shells. They are not native to Manitoba or North America. Adults can grow up to 50 mm (2”) long but most are around 30 mm (1 1/4”) or smaller. When placed on a surface zebra mussels are stable on their flattened underside. Adult zebra mussel colour patterns can vary to the point of having only dark or light coloured shells and no stripes. Unlike our native mussels, they attach themselves to any solid surface, aquatic vegetation or each other with their byssal threads (figure 1).

Figure 1. A cluster of adult zebra mussels attached to a rock. Photo credit: Manitoba Sustainable Development.

Larval zebra mussels are called veligers. They are so small they cannot be seen with the naked eye. Veligers are free-floating in the water and do not attach to hard surfaces until they reach the juvenile stage. Veligers do not swim on their own. Veligers are transported primarily by water movement or transported in standing water aboard watercraft or water-related equipment and conveyances.

Where did zebra mussels come from?

Zebra mussels are native to Eastern Europe and Western Russia. They were brought over to the Great Lakes in ballast water of ocean-going freighters. The ballast water containing aquatic invasive species such as zebra mussels was dumped into the Great Lakes. From there zebra mussels were moved by humans and have expanded their range. In 2009, they were found for the first time in the Red River watershed in Pelican Lake, Minnesota. In 2013 they were found in harbours in the south basin of Lake Winnipeg and are now considered established in the south basin and spreading into the channel and north basin. In 2015, zebra mussel veligers were found in the Manitoba portion of the Red River in June, and in the fall they were found in Cedar Lake by Grand Rapids, Manitoba.

What are their breeding habits and life cycle?
  • Zebra mussels are prolific breeders. Females can produce up to a million eggs per year.
  • Adults start to release eggs in spring when the water temperatures warm to 12°C for a period of 1-2 weeks.
  • The eggs are fertilized in water and become veligers (larval zebra mussels). Veligers may be in the water from late May through October.
  • Veligers float in water for 2-3 weeks and can be moved throughout the lake. They are microscopic so cannot be seen with the naked eye.
  • After 2-3 weeks veligers develop a shell, settle down in the water, and attach to any firm surface.
  • The next summer the mussels become adults and begin to reproduce. They generally live 2-5 years.
What do zebra mussels eat?

Zebra mussels are filter feeders, which means they strain small particles (plant plankton) from the water for food. Thousands of zebra mussels may consume so much plankton that there is not enough for the tiny microscopic animals (zooplankton) that young fish feed on to survive. A single zebra mussel can filter-feed one litre of water per day.

Does anything eat zebra mussels in Manitoba?

Manitoba does not have any native predators of zebra mussels.

Diving ducks can eat mussels. Fish species commonly found in Manitoba such as freshwater drum, lake sturgeon, channel catfish or common carp may learn to eat zebra mussels, even crayfish may also feed on them. However none of these Manitoban predators have evolved with zebra mussels. Generally these predators will not be able to eat enough to significantly reduce or eliminate zebra mussels from a lake or river.

How long can zebra mussels or veligers live out of the water?

Zebra mussel veligers are fragile and generally die within minutes out of water. Settled adult zebra mussels (the stage with a shell) attach to surfaces and can survive up to 30 days out of water depending on the air temperature and humidity. In the spring and fall when temperatures are cooler and there is more moisture in the air, adult zebra mussels can live extended period of time out of water.

What problems do zebra mussels cause?

Zebra mussels can:

  • Impact fish populations;
  • increase water clarity, allowing sunlight to reach deeper into a lake which stimulates more aquatic plant growth and may lead to more frequent algal blooms;
  • clog water intake systems which results in increasing costs for industry, including power and water supply facilities;
  • reduce water-front property values of homes and cottages;
  • block cooling systems of watercraft engines, possibly causing engine damage;
  • kill native mussels by starvation by attaching themselves in enormous numbers (Figure 2);
  • interfere with swimming and beach-going by cutting the feet of swimmers and pets with their sharp-edged shells.

Figure 2. Native mussel (forefront and lighter in colour) being starved by the attachment of numerous adult zebra mussels. Photo credit: Manitoba Sustainable Development.

How do zebra mussels impact fish populations?

Given this recent find it is too earlier to predict the long term impacts of zebra mussels on the fishery in Singush Lake. However, we do know from other areas that have been infested that zebra mussels interrupt the food chain which could negatively affect the growth and survivability of fish populations.

How are zebra mussels spread?

Zebra mussels can be spread by many ways and by many different water-users. For example, zebra mussels can be moved by water-based aircraft, ORVs, recreational and fishing equipment. The overland movement of watercraft and water-related equipment is the primary way aquatic invasive species such as zebra mussels get moved from one water body to another.

Larval zebra mussels called veligers are microscopic. Veligers are arguably the most concerning stage as they cannot be seen but can be carried in water found in bait buckets, bilges, or any other water moved from an invaded lake or river to a new water body.

Adult zebra mussels can start to attach to items left in invaded water bodies such as watercraft hulls, nets, fenders, docks, swim platforms, boatlifts and aquatic plants - anything that is left in the water after roughly 12 hours. Once attached, if not removed, adult zebra mussels can hitchhike on any of these objects and be moved to new, un-invaded water bodies.

Items removed from the water should be inspected by sight and touch. Very small adult zebra mussels attached to a surface, like the hull of a watercraft, can feel like sandpaper.

Where are zebra mussels found in Manitoba?

Zebra mussels are found in Lake Winnipeg, the Red River, Cedar Lake (by Grand Rapids) and now possibly in Singush Lake in Duck Mountain Provincial Park.

If zebra mussels are now in Manitoba, isn’t it too late to stop them?

No, it’s not too late to prevent the overland spread of zebra mussels to new waters. Preventing the spread of zebra mussels will prevent and delay un-expected economic costs to every Manitoban. Once zebra mussels establish they are near impossible to eradicate which can have permanent consequences to the enjoyment of the water body.

Everyone who uses Manitoba’s water bodies must take personal responsibility and accountability for stopping the spread of aquatic invasive species such as zebra mussels. Simple, quick steps such as clean, drain, dry and dispose can prevent an invasion. Preventing the spread will protect what we value about our water bodies.