Inter-Ministry Invasive Species Working Group

Zebra and Quagga Mussel Facts

Zebra and Quagga mussel factsheet

Zebra and Quagga mussel EDRR plan

Origin / Invasion History

Zebra mussels (Dreissena polymorpha) are native to the Black, Caspian and Azov Seas (Benson et al. 2014a) and were first introduced into the Great Lakes through ship ballast water in 1988 and by 1990 they were established in all the Great Lakes and in 1991 they spread into the Illinois and Hudson rivers.

Quagga mussels (Dreissena rostriformis bugensis) are native to the Dneiper River drainage of Ukraine and the Ponto-Caspian Sea (Benson et al. 2014b). The quagga mussel was first discovered in the Great Lakes in 1989 (Benson et al. 2014b). The first reported occurrence of quagga mussels outside the Great Lakes was in 1995; however their distribution is not as widespread outside the Great Lakes as that of the zebra mussel.

Visit the USGS website for the current distribution of zebra and quagga mussels in North America.

Life History

Zebra and quagga are freshwater mussels that mature after 1-2 years, and they are dioecious (separate sexes) with external fertilization. The optimal temperature for spawning is between 18-28°C and a fully mature female mussel is capable of producing up to one million eggs per season (McMahon 1996, Benson et al. 2014a). Eggs are fertilized in the water column and hatch into trocophore larva with no shell which lasts for 6-20 hours after which they become free-swimming veliger larvae after 3-5 days (80-100 µm) (McMahon 1996). This microscopic planktonic larval stage lasts for approximately one month, which can result in long-distance dispersal to downstream areas. They enter the juvenile stage (>400 µm) at around 3-5 weeks which allows the mussel to settle and attach to substrates through byssal threads (McMahon 1996). Before reaching the adult stage, the mussels are most vulnerable to predation, and also require specific temperature, oxygen, substrate and water velocities for successful colonization.

Are Zebra and Quagga Mussels in BC?

At present, no zebra or quagga mussels have been found in BC waters, and the province does have an ongoing monitoring program (see Lake Monitoring webpage for more information). For further information the Zebra and Quagga mussel factsheet is available for download here.

How to Identify Zebra and Quagga Mussels

Distinguishing features of Zebra and Quagga Mussels:

  • Small only up to 3 cm / 1 inch
  • Form dense clumps attached to hard surfaces
  • Propeller blade shaped
  • Zebra stripes often but not always present

Native Mussels and clams:

  • Most species' adults are far larger than zebra and quagga mussels >3 cm/1 inch
  • Either oval or heart shaped
  • Buried, partially buried or on soft substrate or between cobbles
  • Do not form clumps or attach to vertical surfaces

Examples of zebra and quagga mussels:

invasive mussels size in centimetres cluster of invasive musselscompared to size of a quarter
invasive mussels attached to a boat invasive mussels attached to a boat
invasive mussels attached to a boat

In comparison our native mussels are much larger and have a different shape and cannot attach to hard substrate (see pictures below). Additional information on freshwater mussels is available from the BC Species and Ecosystems Explorer and the Freshwater Mussels of the Pacific Northwest (2nd Edition).

Examples of native mussels:

Native mussel Native mussel
Two native mussels

Zebra and Quagga Mussels (top) vs. Native Mussels (bottom):
Size comparison between zebra and quagga mussels versus native mussels

How Do they Spread?

Zebra and quagga mussels have been introduced by trans-continental shipping from the Baltic Sea to the Great Lakes. From there, they have spread throughout North America by attaching to watercraft hauled between waterbodies (Benson et al. 2014a,b). These species can be moved between watersheds while attached as juvenile or adult mussels to watercraft that are transported between waterbodies. Zebra and quagga mussels can survive for extended periods of time out of the water and can be easily overlooked in the smaller juvenile stages when attached to a boat.
Their microscopic free-swimming larvae can also survive for up to 30 days in standing water in boats or other equipment. In October 2013, the presence of zebra mussels was confirmed in Lake Winnipeg, Manitoba, and despite a focused eradication attempt in 2014, mussels were subsequently found throughout the southern basin of the lake.

Provinces and States listed as contaminated under Schedule 5 of the Controlled Alien Species Regulation (October 2014).

Ontario Quebec Manitoba    
Alabama Arizona Arkansas California Colorado
Connecticut Illinois Indiana Iowa Kansas
Kentucky Louisiana Maryland Massachusetts Michigan
Minnesota Mississippi Missouri Nebraska Nevada
New Mexico New York North Dakota Ohio Oklahoma
Pennsylvania South Dakota Tennessee Texas Utah
Vermont West Virginia Wisconsin    

Why Do We Care?

Environmental Impacts

  • Zebra and quagga mussels can substantially alter aquatic food webs which could result in the collapse of valuable native fish populations in BC such as sockeye salmon.
  • Zebra and quagga mussel infestations can lead to increased volumes of macrophytes (native and non-native aquatic weeds) along lake shorelines which can degrade the aquatic environment and water quality.
  • These mussels are also responsible for the extirpation of native unionid mussels (Ricciardi et al. 1998) and have recently been identified as a threat to BC?s Endangered Rocky Mountain Ridged Mussel (Gonidea angulata) by COSEWIC (2010).

Economic/Social Impacts

  • They can clog pipes, water intake systems (hydropower facilities, agriculture irrigation systems), and municipal water supply. This can increase maintenance costs for operating hydroelectric, industrial and agricultural facilities.
  • These mussels can decrease the quality of the recreational experience and impact tourism as mussel shells can injure swimmers along shorelines and next to docks, foul boat propellers and potentially harm drinking water.
  • The economic impact of these invasive mussels to hydropower, agricultural irrigation, municipal water supplies and recreational boating has been estimated to be $43 million per year (Robinson et al. 2013).
  • This estimate does not include additional impacts on commercial and recreational fisheries.
Potential cost impact of invasive mussels on BC's economy