The eastern oyster (Crassostrea virginica) is best known as a seafood favorite that can be consumed a number of ways, from raw on the half shell to fried or in stews. What many may not know is how beneficial the oyster can be to the environment. The oyster feeds on microscopic plants called phytoplankton by filtering seawater. Phytoplankton are naturally occurring and use available nitrogen in the water to grow. In turn, when the oyster consumes phytoplankton, it uses nitrogen to build its soft tissues and shell.

Nitrogen enters the water from a number of sources − both natural, like fallen leaves, and man-made, like lawn fertilizer. Runoff from fertilized lawns has been shown to be a significant source of nitrogen that enters rivers and estuaries. Excess nitrogen has detrimental effects, such as promoting excess algae growth or algal blooms. Algal blooms block sunlight and, when these organisms die and decay, oxygen is consumed from the water column.

When blooms are severe, the oxygen depletion can adversely impact beneficial species, such as fish, invertebrates, and aquatic vegetation. Aquatic vegetation, such as eelgrass, is an important habitat and plays a critical role in the life cycle of another key local shellfish, the bay scallop, a renowned Niantic River inhabitant.

Shellfish, the oyster in particular, are excellent at removing excess phytoplankton and, hence, nitrogen through their filter-feeding process. The adult oyster has a tremendous filtering capacity and in warmer months can filter as much as 50 gallons of water per day! While juvenile oysters do not filter as much water each day, they do filter more per unit of weight than adult oysters as they are growing more rapidly.

Using oysters as a means to remove excess nitrogen is widely considered to be a viable strategy to improve water quality. The Billion Oyster Project (https://billionoysterproject.org/) is an initiative to restore New York Harbor to the healthy estuary it once was by creating oyster reefs. So far, 28 million oysters have been planted in New York Harbor with the goal to plant a total of 1 billion. Similarly, oyster restoration to clean Chesapeake Bay has resulted in 670 acres of seafloor being designated as oyster sanctuaries with almost 4 billion juvenile oysters planted (https://bit.ly/2BzGZhw). The benefits of employing oysters to benefit water quality have also been realized through a shellfish restoration project on Martha’s Vineyard (https://bit.ly/2E94cZx). These are just three examples of both small and very large initiatives to improve water quality by using oysters and their nitrogen removal and water-filtering capacity.

Peter Harris serves on the Waterford-East Lyme Shellfish Commission and the Niantic River Watershed Committee and Don Danila serves on the East Lyme Commission for the Conservation of Natural Resources and the Niantic River Watershed Committee.