Breton and Charent Sea Born Oyster

Oysters are marine bivalve mollusks that play an integral role in coastal ecosystems. They improve water quality through filter feeding, and are useful indicators of environmental conditions. Due to their sensitivity to the salinity and temperature of the water around them, and to the composition of the seabed on which they grow and the plankton on which they feed, oysters reflect the particular flavors of the seascapes they inhabit: they are an excellent expression of terroir.

Human societies around the world have cultivated oysters since prehistory. Traditionally, oysters were harvested and eaten seasonally, in accordance with their life cycle. They are best avoided during the summer, as this is the season when they reproduce, and hormonal changes make them mushy and milky.

The first systems for capturing natural oyster larvae (which are called spat) in the sea developed in the Bay of Saint-Brieuc in Brittany, France, in the 19th century. Today, Natural Breton Oysters are grown from larvae collected in the Arcachon Bay in Gironde, southwest France, where local conditions favor their development. The spat are brought to Brittany and distributed over existing natural oyster reefs, where they mature. After about three years, the oysters are large enough to harvest.

In contrast to these methods, practices such as breeding oysters in hatcheries and then growing them in maturation tanks have been widely adopted in recent decades. Many oyster producers favor these intensive methods, which free them from having to catch spat at sea and then spend time removing each larva from the collecting device. Additionally, spawning can be induced at any time of year, such that reproduction is no longer limited to the summer, and if maturation tanks are used, conditions can be controlled to speed up the oysters’ growth. These techniques, though they improve efficiency, have environmental costs and result in oysters of lesser quality.

In a further attempt to meet increasing demands for oysters, researchers found a way to add a chromosome to natural diploid oysters to create triploid oysters. Triploids are infertile, and thus unaffected by the hormonal changes that compromise the quality of natural oysters during the summer breeding season. They can be harvested throughout the year, and are sometimes called “four season oysters.” Since triploids need not spend any energy on reproducing, they grow faster than diploids and can be harvested after just two years. Seventy percent of the oysters consumed in France today are triploids.

The intensification of production means that oysters are now grown at higher densities than ever before. High densities increase the risk of viral outbreaks, and the French oyster industry has recently experienced a crisis due to a virus that destroys oyster larvae. This virus (OSHV-1), which is becoming more aggressive, proliferates in areas suitable for the growth of the algae that oysters feed on. With increasing competition from larger-scale producers that use hatcheries and maturation tanks to grow triploids, and with the added risk or viral epidemics, many small-scale oyster farmers in Brittany are in danger of going out of business.