Oyster 101
Oyster Larvae and Settlement
Practical oyster knowledge from the people who grow, harvest and handle them on Willapa Bay.
Settlement is the moment an oyster stops being a drifting larva and becomes a permanent resident of a particular place. It is one of the most consequential stages in both wild oyster ecology and hatchery production.
Larvae begin in the plankton
After fertilization, oysters pass through several larval stages while suspended in the water column. They feed on microscopic algae and are transported by currents.
Development changes what the larva can do
As larvae grow, they develop a shell and swimming structure called a velum. Near the end of larval life, they develop a foot and become capable of exploring surfaces before settlement.
Larvae do not settle just anywhere
Suitable settlement depends on surface texture, chemistry, biofilms, salinity, temperature and other environmental cues. Oyster shell is especially valuable because it offers hard, chemically familiar substrate.
Attachment is permanent
Once the larva cements itself to a surface, it metamorphoses into spat. From that point forward it cannot relocate to another bed under its own power.
Why hatcheries manage settlement carefully
Hatcheries can allow larvae to set on whole shell, shell fragments or very small particles depending on the intended grow-out method. Single-seed culture is designed to produce individual oysters that can later be graded and moved through nursery systems.
Why settlement matters in restoration
A restoration site can contain adults and still fail if larvae cannot find enough suitable settlement surface or if new spat do not survive. Recruitment is therefore a core measure of whether a native oyster population is becoming self-sustaining.
Go deeper
Continue with Shellfish Hatcheries and Seed, Oyster Life Cycle, and Olympia Oyster Restoration.