River Life: Oysters and the “R” months

Every year seems to pass faster and faster, so here we are in September with Halloween costumes and decorations already in the stores. Thanksgiving and Christmas will be here before we know it. It must be fall.

As someone who grew up on the Chesapeake Bay near Norfolk, Va., fall means Oyster Roasts and Blue Crab Boils. My family followed the rule to only eat oysters in months with an "R" in them. Oysters were better from September to April, the "R" months, and not as sweet and tasty from May to August, the non-"R" months. As a youth, I had no idea why, but accepted the rule as Gospel.

As a marine biologist, I came to realize that it all came down to what the oysters are eating and when they reproduce. Oysters are a little different in how they reproduce. They do not follow the traditional male-female role that once a male, always a male, that we see in many species. Oysters start life as a male, but they are protandric, meaning they change from male to female over their life span.

The smaller males produce sperm while the larger females produce eggs. There are some species that can go from female to male (protogymy) and a few that can go back and forth depending on various factors (sequential hermaphroditism). Nature is full of variations when it comes to ways to do things. It is seldom a simple yes or no.

During an oyster's spawning season, the young males release sperm as the older females release their eggs. There can be millions of eggs. Once they meet, they develop into larvae that swim around searching for a suitable surface to settle, attach and grow. At that time, they are spats. After a few weeks, they grow as males for about the first year of their life.

By the way, the preferred settling surface for an oyster spat is another oyster shell. Attaching to another oyster indicates to the spat that an oyster had successfully survived and lived at that spot previously. Pretty neat evolutionary tactic. It is also a strong reason to recycle oyster shells and return them to the area where they were harvested. This is a practice that is not always possible.

That gets us to why the "R" months are the best months to eat oysters. As mentioned, the larger and usually preferred oysters are females. They grow and accumulate glycogen, which is a branched glucose (sugar) polymer. Glycogen is the key factor in flavor and taste. It is required in significant amounts for the oyster to produce eggs. They store glycogen during the "R" months, then use it as they release their eggs during the spawn.

Oysters become a mere shadow of their pre-spawn self once they release the eggs during those non-"R" months. They are no longer the preferred large juicy ones we want to eat.

Oysters reach an edible size after about three years and can live up to 20 years. They are filter feeders, and up to 50 gallons of water passes through their gills every day. Oysters are not only good to eat, but an extremely important factor in maintaining water quality.

Glad you asked River Life

Can you eat oysters from the St. Johns River? What can we do to promote oyster growth in the St. Johns River?

Regretfully water quality in the St. Johns River does not allow the oysters that grow in the river to be harvested and eaten. But that doesn't mean we should not try to promote oysters to grow in the river. In fact, the Coastal Conservation Association, St. Johns Riverkeeper and Jacksonville University Marine Science Research Institute are teaming up to make Vertical Oyster Gardens, which are oyster shells on a length of rope or wire that homeowners can hang on their docks. The first demonstration of how to build them will be at Florida FinFest at Jacksonville Beach on Saturday, Sept.14. This free musical festival also has educational programs on Friday afternoon and all-day Saturday.

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