Zebra mussel

Zebra mussel facts

Scientific name: Dreissena polymorpha

Family: Dreissenidae

Diet: Detritus, plankton and bacteria

Size: 2-4cm

Weight: 6-18mg

Lifespan: 4-8 years

Zebra mussels in Britain

Zebra mussels were first recorded in the UK in 1825, and are believed to have found their way from the Baltic Sea on timber imported on ships.

These molluscs are drawn to slow rivers, canals, and open water spaces like reservoirs. They rapidly form large colonies that attach to almost any submerged hard surface including pipes, stones, boats, lock gates, and even waterway banks.

Not only do they negatively impact native flora and fauna, they can also clog pipes and affect water flow.

Why are zebra mussels a problem for canals?

Zebra mussels are filter feeders. They suck in water, retain the nutrients, and spit out the rest. Whilst it probably sounds like filtering water is a good thing, these molluscs can each filter up to one litre a day. As a result, the water is rid of vital nutrients and oxygen, which can cause severe problems for native wildlife populations, and suitable habitats.

Increased water clarity also means that sunlight is better able to penetrate the water and stimulate the growth of invasive plants like floating pennywort.

Zebra mussel larvae can drift downstream for as long as 3-4 weeks, and cover up to 300km before finding somewhere new to spawn. However, they are mostly spread through recreational boating and angling, when the mussels attach themselves to a boat's hull or some equipment and are then transported to other areas.

They are even able to survive out of water in cool, damp conditions for up to three weeks. This makes it incredibly important to follow the 'Check, Clean, Dry' process each time you exit a canal or river to prevent their spread - even if you're relocating to another spot close by.

Why are zebra mussels a problem for native wildlife?

Zebra mussels have a detrimental effect on the native swan mussel population, and are responsible for drastically altering the ecology of the waters in which they live by changing fish populations. This happens when zebra mussels take over spawning grounds and change the populations of animals that the fish eat.

How to identify a zebra mussel

Zebra mussels are aptly named due to their striped markings, which can be a blend of blue, brown, white and soft yellow. These colours are usually more prominent in a live mussel, rather than one that has died.

They are a distinctive 'D' shape, and their shells are strong and thick without any teeth on the hinge.

How do zebra mussels breed?

This mollusc is a prolific breeder. An adult mussel can produce up to one million eggs a season, and each one of these has the ability to establish a new population. Their spawning generally takes place in the spring and summer, and can go on for as long as 3-5 months.

What animals eat zebra mussels?

Various fish species including roach, carp and eels will eat zebra mussels.

Crayfish, muskrats and diving ducks like pochards are also partial.

Other invasive species on our canals