Shellfish harvested in the fall incorporated more nitrogen, which Reitsma said wasn’t a surprise, since oysters and quahogs tend to “fatten up” in the fall in preparation for the winter season. “Multiply those numbers by the number of shellfish harvested and you can assess how much nitrogen is removed from the waterways, and how much less nitrogen has to be removed by other means,” said Matt Charette, director of the Woods Hole Sea Grant program. “More shell means more nitrogen that the animal has stored in that shell.” “Wild oysters or bottom-grown oysters, which deal more with predators, have to grow thicker shells for protection,” Reitsma said. 32 grams of nitrogen-more than those grown in floating cages. Wild oysters and those grown on pond bottoms contained an average of. 28 grams of nitrogen, and quahogs contained. Their analyses showed that individual oysters, on average, contained. They gathered samples of both wild and farmed oysters and quahogs from various water bodies in Cape Cod. To find out, Sea Grant and Cooperative Extension researchers joined with the Mashpee Department of Natural Resources to measure the nitrogen removal capacities of shellfish harvested from Cape Cod waters. Researchers from WHOI Sea Grant and the Cape Cod Cooperative Extension analyzed wild and farmed oysters and quahogs to see how much nitrogen they can store in their shells to assess how much excess nitrogen they can removed from coastal waters. But how much nitrogen ends up in their tissue and shells? That represents how much nitrogen would be removed from the water when the shellfish are harvested. Towns are considering seeding and growing shellfish as a way to reduce nitrogen levels in coastal waters because they are a cheaper and faster alternative to building sewers and wastewater treatment systems that could cost billions of dollars, said Joshua Reitsma, a marine specialist with the Woods Hole Sea Grant Program and Cape Cod Cooperative Extension.Īdult oysters reportedly can filter up to 50 gallons a day, while large quahogs (hard clams) can clean about 24 gallons of water a day. Oysters, clams, and other shellfish are efficient filter feeders that help remove excess nitrogen from waters by incorporating it into their shells and tissue as they grow. Nitrogen is an essential nutrient for plants and animals, but too much nitrogen-often from fertilizer runoff and septic tanks-boosts the growth of algae, which overwhelm water bodies and ultimately reduce oxygen levels in them. Like a snail shell becoming a home for a hermit crab, old oyster shells become a nursery for the next generation.Towns in Cape Cod are looking to shellfish not only as culinary treats, but as a way to help clean up waters suffering from excess nitrogen. Although several species of oyster can live on muddy bottoms, they thrive when able to attach to a hard surface (another reason to leave shells on the beach!). If you look closely at an empty oyster shell on a Puget Sound beach, you may be able to see spat-which can look like anything from a small black dot to a fingernail-sized small oyster-clinging to it. This allows Olympia oyster larvae to have slower rates of growth and shell-building during this phase, possibly easing the energetic burden of trying to build a shell in conditions of OA. But Olympias are unique in another way: most oysters are broadcast spawners, while Olympias brood their young for 10–12 days, during that critical period of initial shell formation.

For example, unlike many oyster species, our native Olympia oysters show no negative effects when exposed to different levels of OA.

We also know the changing chemistry of the ocean is a complex process with varying effects from species to species. Ocean acidification (OA) has been shown to cause delay of shell formation, weaker shells, and therefore increased mortality in larval oysters, as well as decreased growth and shell-building in adult oysters. At this point, the young creature switches from building a shell of aragonite to building one of calcite. The larva continues life in the form of plankton for the next two to three weeks, feeding on microalgae, until it grows a foot to stick down to a hard surface. Pacific oysters, for example, begin building their shells 14–18 hours after the egg is fertilized, laying down a shell made of aragonite. As an animal’s body pulls calcium carbonate from the water, it may be laid down in different formations, mostly commonly either calcite or aragonite, to form a shell. We know that ocean acidification decreases the amount of calcium carbonate building blocks available in the water for these and other shell-building animals to use as they grow. Five species of oysters are cultivated for food in the Puget Sound region: the Kumamoto (Crassostrea sikamea), the Pacific (Crassostrea gigas), the Eastern (Crassostrea virginica), the European (Ostrea edulis) and-the only native species-the Olympia (Ostrea lurida).

Algae species feed for oyster spat