A Scallop’s Life

Rachael Norris and Marina Freudzon
A bay scallop

When our harbors and bays begin to warm, somewhere around 60 to 70 degrees Fahrenheit, the reproductive organ of an adult bay scallop (Argopecten irradians) begins to produce gametes (sperm and eggs) simultaneously.

Yes, bay scallops, which only live two years, are true hermaphrodites, having both male and female sex organs. Other bivalves, such as clams and oysters. are known as protandric-hermaphrodites, meaning they mature as males but can switch to females later in life.

When marine waters reach optimal spawning conditions, a reproductive mature bay scallop will alternately release millions of eggs and sperm into the water column. These gametes will be at the mercy of tidal currents, carrying them throughout the Peconic Bay Estuary system with the expectation of connecting with opposite sex gametes.

If haploid sperm and egg connect, fertilization takes place and a microscopic zygote is formed. This zygote, known as a bay scallop larva, will become a food source for countless filter-feeding marine animals. Only one-in-a-million scallop larvae will survive this stage.

If not swallowed by an Atlantic menhaden or other shellfish, in two weeks, the swimming larva will metamorphose, and produce a hard shell made of calcium carbonate. As the shell begins to take shape and becomes strong, the juvenile scallop will slowly sink to the bottom and attach itself to a substrate, preferably eelgrass or some other marine plant. It is here the juvenile scallop will stay for the rest of the year and seek shelter from bottom-dwelling predators.

For nourishment, the baby scallop will filter water through its gills, extracting both oxygen and nutrients at an astounding rate. This allows the scallop to grow quite rapidly, reaching nearly two inches by year’s end. As the temperature drops below 50 degrees, the juvenile scallop will filter nutrients to gain the energy storage necessary to go dormant and survive the winter. This energy reserve is in the form of sugars (glycogen), and is why the adductor muscle tastes so sweet during the harvest season.

As spring arrives the following year, the scallops will wake from their dormant state and begin filter-feeding again on the spring algal blooms. These algal blooms allow these now reproductively mature scallops to filter in the required nutrients for the development of their reproductive organ, and prepare for the release of the next generation into our waters.

Frank Quevedo is the executive director of the South Fork Natural History Museum.

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