Zebra Mussel (Dreissena polymorpha)

Zebra mussels, named for the distinctive zigzag “zebra” banding on their brown and yellow shells, are sessile bivalves that negatively impact native biodiversity and ecosystems. Zebra mussels arrived in the UK in the 1820s and since 1999, there has been a significant increase in their numbers, predominately in England. Arrived in Ireland in 1994 attached to the hulls of second-hand boats imported from Britain or the Netherlands. It is also now present in Northern Ireland.

Adults of this species attach to solid surfaces, such as boats, facilitating their introduction to new areas. They are commonly found in slow-flowing rivers, canals, water pipelines, and water treatment facilities. In treatment or extraction facilities, zebra mussels are highly disruptive to processing and are also detrimental to native swan mussel populations. Their larvae are sensitive to UV light, therefore they are not normally found below 1m in depth. Commonly confused with the closely related Quagga Mussel.

• Avoid stepping into the water – this can stir up sediment, throwing up sediment DNA and any inhibitory molecules present. Sediment may clog the filter and prevent sufficient volumes of water being filtered.