This small but prolific mussel is a native of the Caspian and Black Seas region and was introduced through ballast water to the Shannon Estuary in the 1990s. Zebra mussels live in freshwater and in the upper reaches of tidal estuaries.
They have spread from this area, principally via boat movements, throughout the Shannon and Shannon-Erne catchments. The female mussel can release up to 1 million eggs each year.
These are carried in water currents and settle out after approximately three weeks. They are filter feeders and remove much of the plankton that juvenile fish depend upon. Hence, they may cause an imbalance in fish communities.
They attach to hard surfaces such as boats, buoys and water intake pipes, where they form very dense clusters. As such, they can cause problems by blocking intake pipes and clogging cooling systems.
Distribution of zebra mussel in Ireland