<P> In 2012, the National University of Ireland, Galway, said "The discovery of zebra mussels (Dreissena polymorpha) in Lough Derg and the lower Shannon region in 1997 (McCarthy et al 1997, a & b) has led to considerable concern about the potential ecological and economic damage that this highly invasive aquatic nuisance species can cause ." </P> <P> The lifespan of a zebra mussel is four to five years . A female zebra mussel begins to reproduce within 6--7 weeks of settling . </P> <P> An adult female zebra mussel can produce 30,000 to 40,000 eggs in each reproductive cycle, and over 1 million each year . Free - swimming microscopic larvae, called veligers, drift in the water for several weeks and then settle onto any hard surface they can find . Zebra mussels also can tolerate a wide range of environmental conditions and adults can even survive out of water for about 7 days . </P> <P> Research on natural enemies, both in Europe and North America, has focused on predators, particularly birds (36 species) and fish (15 and 38 species eating veligers and attached mussels). </P>

Population of zebra mussels in the great lakes