Bivalves filter nitrogen from Island waters

Eat Shellfish, Save The Ponds

by Amandine Surier

Eat Shellfish, Save The Ponds

Carole Topalian

My affair with bivalves started early. As a typical Parisian child, I grew up vacationing on the Normandy coast. On clear days, my sister Aurélie and I would roam the half-mile beach flats left behind by the monumental Channel tides, filling our buckets, pockets, and sweater sleeves with the delicious common cockle, Cerastoderma edule. At the dinner table, swooning in front of a steaming bowl of garlic cockles, I fell in love.

As a student of marine biology at the University of Paris VI, my classmates and I did not share the same shellfish infatuation. When most of them wanted to save the North Atlantic right whale, I wanted to grow shellfish.

Bivalves might not seem worthy of a life-long commitment, but there is more to them than meets the eye. Not only are they humble, beautiful, and delicious, but they’re also good for our ailing planet. Like pocket-size water purifiers, they are capable of removing nitrogen from the water, something even humans haven’t quite figured out how to do.

Where people go, nitrogen follows. Every time a septic system fails, or someone fertilizes a lawn or crops and rainwater runs down roads or parking lots, excess nitrogen enters the watershed. Too much nitrogen, and ponds become thick, overgrown algae jungles, blocking light and turning bottoms into zero-oxygen dead zones. Not a pretty picture.

Two types of algae cause the familiar murky waters: seaweed and phytoplankton. With seaweed, our removal options are limited. Eating more seaweed would certainly help both ponds and humans, but that’s a story for another day. With phytoplankton, bivalves are the perfect critters for the job.

Bivalves have remarkable gills. While most fish gills are solely in charge of gas exchange (oxygen in, carbon dioxide out), bivalve gills are also specialized for feeding. With their mucus-covered hair-like cilia, the gills are capable of trapping small particles and directing them towards the mouth. The water goes in rich in phytoplankton and comes out clear—a simple and extremely efficient bio-filter.

On average, an adult three-inch oyster filters between 30 to 50 gallons of water per day. That’s the volume of an old whiskey barrel or your grandmother’s claw-foot tub. As the oyster is consuming phytoplankton, it is also integrating the nitrogen into its flesh and shell. When the oyster is harvested, the nitrogen leaves the system. Voilà. A weekly harvest of 200 oysters can compensate for the nitrogen input of a typical waterfront homeowner.

I washed up on Vineyard shores eight years ago, still following the shellfish trail. “Hatchery Manager Wanted,” said the ad, “Must be able to lift 30 pounds.” With my masters in Shellfish Culture in hand, I put my green suitcase down on the Steamship Authority docks one night in June, unaware that I had reached bivalve Mecca.

On the Island, most locals are well aware of the greatness of shellfish and are determined to preserve working waterfronts. It is a matter of culinary pride that Katama Bay in Edgartown has recently emerged as one of the best oyster-growing bays on the east coast, with Sweet Neck Farm tying for third place at a tasting of oysters from all over the East Coast in Washington, D.C. Today, seven oyster farmers are currently in business in the Bay, which holds 1.2 million oysters just shy of three inches, and another 4 million seed the size of a coffee bean. With a weekly harvest of 12,000 to 28,000 oysters, these 3-acre farms and the men and women who tend them compensate for the nitrogen input of up to 140 waterfront homeowners.

The Island waters also hold large beds of wild oysters, quahogs, mussels, and soft-shell clams, as well as one of the last sustainable bay scallop commercial fisheries in the world. To protect from overfishing and to maintain the delicate equilibrium of these shellfish beds, each Island town has a shellfish department and every year our waters are planted with millions of seed produced by the MV Shellfish Group in Vineyard Haven, where I’ve been working now for almost a decade. Together with town constables, our hatchery crew makes sure each year that these wild critters remain abundant and keep filtering relentlessly to give us the clean waters that we love.

So while on the Island, take advantage of this fantastic resource. If you feel like getting your feet wet, purchase a shellfish license at your local town hall and grab your rakes, or simply go to your fishmonger and ask for local shellfish, because there is nothing better than eating a delicious meal that is also good for the environment.