Life Cycle - The zebra mussel lives from 4-6 years in European waters. In the Great Lakes its life span has been observed to be a maximum of three years. They become sexually mature at about one year of age. Spawning is triggered by factors like temperature and phytoplankton abundance.
Egg Stage - an average adult female can produce 30,000 to 40,000 eggs per season. Eggs are released into the warm water and the male mussels sense the presence of the eggs around them and release sperm into the water.
Veliger Stage - Several hours after fertilization the larvae, known as veligers, emerge. They have a clump of hair-like filaments called cilia that help suspend them in the water. During this time they feed heavily on plankton and grow in size.
Post-Veliger Stage - When they attain a size of about 200 um, the veligers are too heavy to remain afloat. They settle on the bottom and try to find a hard surface to which they can attach. Attachment of the post-veligers is made possible by byssal threads which are secreted.
Settling Stage - Within the next three weeks, post-veligers transform into juveniles forms. These resemble adult mussels and attain maturity the following year. Juveniles often detach their byssal attachment and move around, trying to locate areas with abundant plankton supplies.
Adult Stage - A Zebra Mussel attains about 2.5 cm (1 inch) in the first year and adds another 1.25 to 2.5 cm during the next year.