Oysters within an area tend to spawn at the same time, although they may spawn more than once in a given season depending on conditions. Since oysters demonstrate a degree of synchronized spawning and the larvae are only able to settle for a short time, it is important to understand how the timing of larval settlement throughout each year may change from location to location. 

The Oyster Spat Monitoring Program is one of the first efforts to coordinate oyster larvae sampling along the north, central, and south eastern coast of North Carolina. The key to this project is keeping our artificial settlement substrate, "Spat Rack," in the water year-round.

Oyster larvae begin searching for suitable settlement substrate when they reach the veliger “eyed” stage. This occurs a few weeks after the larvae have spawned. This pigment patch is not a true eye, but is sensitive to light, so the larvae will remain near the substrate.  

When the “eyed” larvae encounter a good settlement substrate, they secrete a form of biological glue to attach themselves and begin life as an oyster.

Oyster larvae are “competent”, or able to settle, for about two weeks. Larvae will die if they do not find a suitable settlement location after this two week period. Although many studies have tried to determine exactly what cues the larvae use to settle, it is still not clear. 

We do know, without any doubt, that the larvae prefer the shells of other oysters. For our study, we use ceramic tiles as settlement substrate. The tiles serve as a good surrogate for actual oyster shell, and their uniform surface area simplifies our sampling and data parameters.