The common blue mussel (Mytilus edulis) has several stages in its life cycle.The first stage occurs when two adult mussels produce and release eggs and sperm into the ocean (1). After fertilization, which usually occurs in mid-May to late June, the fertilized egg begins to develop into a free floating larval form of the mussel known as a trochophore (2).
These partially developed mussels will float around in the ocean as it’s major body parts and systems develop. This free floating larval form usually exists for a typical duration of three to four weeks, at which point it reaches what is known as the settlement stage (3).
Eventually, these floating larvae mature and attach themselves to a suitable growing surface. This could be a coastal rock, a pier or as in the aquaculture industry a collector line . Once they have attached,they excrete a material which hardens upon contact with sea water to form the byssal threads. These filaments are incredibly tough, with a tensile strength of 20 - 30 pounds, and latch the mussel fiercely to it’s new home. It is at this point which the mussel grows and matures into a fully developed mussel.
The blue mussel, as with all mussels, reproduce sexually. There are separate sexes which release gametes (eggs and sperms) directly into the water and as such mussels utilize both external fertilization and development. It takes the new generation of mussels between two to three years before they reach sexual maturity. The major spawning periods take place during the summer although a major spawning may take place anytime from late spring to late summer. During their spawning season, the mussels lose about one half of their meat weight.
Although it is not fully understood what triggers the mussels systems to begin spawning, we do know that the temperature and salinity of the water play a very important role in determining when the best time to spawn will be.
When the conditions are right and spawning occurs, the female mussels release tightly formed clumps of eggs into the water which will be fertilized by the male sperm. One single female mussel is capable of producing and releasing as many as 25 million eggs per spawn.After fertilization the mussel zygote deveolops into a mobile larva called the trochophore larva.
This stage is referred to as "mussel spat". These swim and float in the coastal water for a short time and then settle and attach to a growth medium such as the bottom, intertidal rocks, or man-made structures. They grow to marketable size in about 3 years , depending on environmental conditions. Once they become sexually mature they will typically spawn each spring (late June to early July).