If you’ve spent any time around commercial oyster farming, you've probably heard terms like seed, spat, SoS and florets. They can sound a little confusing at first, but they’re really just names for different stages in an oyster’s life.
It all starts in a hatchery. Adult breeding oysters, called broodstock, are encouraged to spawn by changing the water temperature and introducing natural chemical signals into the spawning tanks (Figure 1).
The broodstock release eggs and sperm (Figure 2), which are mixed together for fertilization. Within about 12 hours, the fertilized eggs develop into tiny free-swimming larvae called trochophores. By the next day, they usually reach the veliger stage.
The name “veliger” comes from Latin and means “sail bearer.” These larvae have a tiny sail-like structure called a velum that helps them swim and feed.
In the hatchery, veliger larvae are raised in tanks and fed phytoplankton (Figure 3). As they grow, they become pediveligers, meaning they develop a small foot. They use this foot to crawl around and search for the perfect place to settle down. Once they find a suitable surface, they attach permanently using a natural cement-like substance. This process is called setting.
Spat
Once an oyster larva attaches to a surface, it’s called spat.
What happens next depends on what it attaches to and how it’s raised.
Seed
Commercial oyster farmers usually want oysters that grow individually. To make that happen, hatcheries use micro-culch, which are tiny pieces of oyster shell. Each piece is just large enough for one larva to settle on, preventing multiple oysters from attaching to the same spot.
After setting, the young oysters grow as individuals and are called seed (Figure 4).
Seed are typically raised in a nursery until they reach about 6-9 millimeters in size. At that point, they can be sold to growers, usually by the thousand. Some hatcheries also sell oyster larvae directly to nurseries, which then handle the setting process themselves.
Spat on shell (SoS)
Another option is to let pediveligers settle on larger, cured oyster shells. These shells have been cleaned naturally by exposure to sunlight and outdoor conditions.
When this happens, many oysters can attach to the same shell. This product is called spat on shell, or SoS (Figure 5).
As these oysters grow, they form clusters similar to those found on natural oyster reefs. Spat on shell is commonly used for reef restoration projects, educational oyster gardening programs and some forms of on-bottom oyster farming.
Florets
Now we get to florets (Figure 6).
This is a newer term used to describe spat-on-shell that are grown in protective cages until they develop into small, living reef communities. As they grow, they start to resemble broccoli or cauliflower florets — hence the name.
The term was created because it’s more appealing and easier to market than simply calling them “clusters.” Since they can be produced using commercial oyster farming methods, there is growing interest in their use for restoration projects.
Florets can be produced in different sizes, but those grown in farming systems typically contain around 11 oysters per floret. When they’re ready to be deployed, the young oysters are usually about 1 inch (25 mm) long.
Researchers are currently studying how well florets perform compared to other reef restoration methods. New projects are also exploring the costs of large-scale floret production, potential market demand and whether producing florets could provide an additional source of income for oyster farmers.
Bringing it all together
Here’s the simple version:
- Spat are newly attached oysters.
- Seed are spat that grow individually.
- Spat on Shell (SoS) are multiple oysters growing on the same shell.
- Florets are groups of spat-on-shell that have grown into small reef-like structures.
No matter what stage they’re in, oysters provide valuable benefits. They help filter water, create habitat for fish and other marine life, and support healthy coastal ecosystems.
Andrea Tarnecki contributed to this blog post.
Meet the author
Russell "Rusty" Grice
Oyster Aquaculture Business Specialist
Rusty joined Sea Grant in 2016. He helps oyster farmers navigate requirements for starting farms, and he helps streamline the harvest reporting process for existing farms. His focus is on... Read more
Phone: 251-229-0826
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