Farming Oysters

When humans first encountered oysters, they seemed limitless. Generations of aggressive oyster harvesting decimated wild oyster populations. Now, most commercial oysters you eat at restaurants come from farms. The process of farming oysters is quite involved. The methods vary depending on geographic region and the preferences of the farmers. Farming will often begin with selecting the appropriate adult oysters for breeding. As in other kinds of farming, farmers breed for traits like disease resistance, fast growth, and shape. Farmers stimulate oysters to breed by placing oyster in special tanks. These tanks and manipulating the temperature and amount of food, causing oysters to spawn. Once oysters breed, the fertilized eggs will become free-swimming larvae. These larvae number in the millions. After a few weeks they will be ready to attach to whatever surface they can find. Farmers provide platforms of ground shell, called clutch. The young oysters, called spat, cement themselves to it.

There are two main methods to farming oysters: bottom culture and the off-bottom culture. Bottom culture uses the natural sea floor as the base for oyster farms. Bottom culture better simulates a natural oyster environment. Bottom culture often produces oysters with stronger shells. This may be due to minerals on the sea bed or a natural adaptation to a more hostile environment. Bottom culture leaves oysters more exposed and often not all survive.

Off-bottom culture involves growing oysters in controlled environments that float in the open water.  This is a safer environment for the oysters to develop. There are many forms of off-bottom culturing, some of which include cage culturing, rack and bag culturing, and tray culturing. Each method has its own advantages and disadvantages.

Whichever method the farmers use, oyster farming is very good for the environment. Because of oysters' ability to clean water, it’s one of the only forms of farming that leaves the surrounding area cleaner than it would be otherwise.

How do oysters make pearls?

The luminous and beautiful gems we call pearls are calcium carbonate spheres produced by some species of oyster. The Eastern oyster, which dominates the US, doesn’t produce pearls. While we value pearls world-wide, we still don’t know much about why oysters produce them. Whether naturally grown or cultured, an oyster does not need or want to create a pearl in the first place.

The pearl is the result of an irritant which gets stuck inside the oyster’s soft tissue. This is often an insect or debris. The oyster’s body recognizes the foreign material and surrounds it with cells until they form a pillow called a “pearl sac”. This sac starts releasing a calcium carbonate substance called “nacre” which coats the foreign object. This protects the rest of the oyster’s body. As long as the object remains inside the shell, the oyster will continue to coat in layers the nacre. This keeps the pearl growing in size. The longer the pearl stays in the oyster, the bigger the pearl. Contrary to what you might see in stores, most pearls are irregular in shape and color. Few naturally form the well known, perfectly round sphere with exceptional color and luster. Other shell-based living creatures like conch, clams, and mussels are also capable of producing pearls.

Nacre also coats the inside of oyster shells. This creates the beautiful and lustrous substance known as mother-of-pearl. Humans have used mother-of-pearl for generations in manufacturing everything from buttons to furniture. Craftsmen grind down the outer shell, leaving only the layers of nacre.