What is an upweller?

Under the leadership of Jennifer Filiault and Steve Parks, the MOP team has begun construction of an upweller at the Maritime GloucesterMuseum to raise infant oyster spat to a 2 inch size so that they can be used for oyster propagation.

An upweller is a system of tanks that flow seawater over the oyster spat so that it receives a good flow of nutritious water for it to filter and feed on. The oysters filter out the plankton, digest it and use the nutrition to grow.  A typical upweller contains the oyster spat in containers with screen bottoms. The water is forced up through the screen bottoms around the oysters and out the top where it is returned to the ocean or estuary.

Diagram of an Upweller Oyster Nursery

The screen is changed over the course of a growing season as the oyster spat grows. Initially we are starting with the finest mesh screen we could get at Home Depot. It can even keep out No-see-ums! Over time our interns will be changing the screen to larger and larger mesh sizes.

Adding Screen to the Buckets

Bucket with Screen for Upweller Oyster Nursery

There are several types of upwellers and they are largely classified by their location. They can be in the water beneath a dock, near the water on a floating dock, or in our case, on structures. Ours will be located on a dock at Maritime Gloucester.

In mid-June we will be receiving 60,000 baby oysters or spat. They will be approximately 1-2 millimeters in size. They will be delivered via FedEx in a coffee can sized container. While they start off small, they will grow fast. By September they will be 2 inches long. It is amazing to see the growth!  

When we first started restoring oysters to Boston Harbor we experimented with some dime sized oysters. From August 9^th to September 9^th they grew from the size of a dime to the size of a quarter! It was an amazing transition that filled us with excitement seeing the oysters could grow so robustly.

As we move into fall the oysters will be 1.5-2 inches in length. They will begin storing glycogen for the winter when they go into hibernation mode. At seasons end, we will test the oysters to be sure they are safe, and then find them a new home.  

To learn more about bvuilding an upweller you can visit this PDF file..

A Bit About Raising Oysters for Pearls in Polynesia

One of our Board members is in the jewelry industry. She is learning more about pearls. She provided this information about growing the oysters. 

Pearl farms in French Polynesia don’t operate hatcheries, so the collection of wild shell is of paramount importance. Spat are collected by placing objects, such as dark plastic mesh, to lines a few feet below the water’s surface. As spat float by on the current, the baby mollusks attach themselves to the object using their byssus (foot).

Spat collectors with thousands of shells attached

After six months, the spat collectors are taken to the surface, and the baby mollusks are removed. A single collector might host 15,000 baby shells. They are placed into special baskets and hung from growing platforms at depths  of up to eight meters.

Three black-lipped shells at various stages of growth

When the shells are nearly adults, they undergo their first operation—one that is unique to pearling operations that utilize black lips. They are pulled from the water, and a small hole is drilled through the shells. There is no danger to the animal during this operation as the piercing is just outside the hinge. A nylon rope is then inserted through this hole and tied. This process is repeated, resulting in a chain, or chaplet, of ten to twenty pearl mollusks. The chaplets are returned to the platform for the final grow-out of the young shells.