Zebra and quagga mussels have separate sexes and eggs are expelled by females to be fertilized outside of the body by males, usually in the spring or summer. The microscopic larvae, called veligers, emerge within 3-5 days and are free swimming for up to a
month, being dispersed by water flow.
After this time the veligers search for an attachment site, and metamorphosis and secretion
of the adult shell begins. The mussels
may reach maturity in the first year, but the second year is more usual.
A fully mature female mussel is capable of producing up to one million eggs per season. These non-native mussels are filter feeders and each mature adult is capable of filtering
at least one litre of water per day, removing plankton, algae, and even their own veligers. Any undesirable matter is ejected as pseudofeces.
Filtering by these mussels increases
water transparency and light penetration, decreased organic matter, and increased concentrations of ammonia, nitrates, and
phosphates. Only certain algal species are consumed - cyanobacteria are not - leading to toxic algal blooms, which deplete the oxygen in the water, killing fish and plants