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Towns Look to Oysters to Clean Waterways

Sarah Tan



Some town waterways on the Cape will soon be getting an influx of oysters.  It’s an intervention that town managers hope will have multiple benefits for the water quality, the ecosystem, and for local shellfishermen.




Last week, over at an oyster hatchery called the Aquaculture Research Corporation in Dennis, workers were busy tossing bags filled with old clamshells into a cement tub the size of a pool. The hatchery is preparing to sell bags and bags of these shells with this new oyster larvae on them to local towns. And since 2004, towns like Mashpee, Chatham, Truro and Dennis have bought these oysters from the hatchery and used them to filter out local waterways suffering from over nitrification. Rob Doane, president of the hatchery explained.

"That comes from fertilizers on your lawn, from septic systems, which basically is clouding the water with algae," Doane said. "So there’s an abundance of algae in these embayments and that’s food for oysters."

Nitrification happens when pollution from sewer runoff leaks into waterways causes excess nitrogen, and that excess nitrogen causes algae overgrowth, which then kills fish and plants. But, oysters love algae, and towns love the all-purpose bivalves because they can clean water, rebuild natural oyster reefs and allow for a resurgence in wild shellfishing in the area all at the same time.  

"One oyster can filter forty gallons of water per day, and we’re putting ten-thousand on all of these bags, so towns are taking anywhere from one-hundred to two-thousand bags each and they’ll be using that for their oyster reefs and to clean the water," Doane said.

But to get them to the point where they can grow in the wild, first, the oysters need to be prepped at the hatchery. Oysters start life as microscopic larva, with finger-like hairs that propel them through the water. But as they mature, they grow an eye and a foot. The eye urges them to move away from light, and the foot has a drop of cement-like substance that will glue them to a hard surface - in this case, when the larva are poured into the pool filled with empty shells, they’ll adhere to the shells and grow on top of them.

"Wild shellfish populations are down to one percent of their historic levels, so in this way we’re adding as many oysters as we can and cleaning the water while we’re doing it," he said.

The town of Mashpee has been using oysters from the hatchery and putting them into nearby bays for over ten years and since then, they've seen much less fish death from algae.

"It’s an alternative that’s kind of a win win, because you get shellfish and you get the water cleaned up," Rick York, director of natural resources for Mashpee said.

And for fiteen dollars a bag, he said it’s much cheaper than a complicated sewerage system that would filter the water.

"The conservative estimate from our comprehensive plan is that the shellfish option, if it works, could save two-hundred-million dollars, just for the town of Mashpee," York said.

But Diane Murphy, the fisheries and aquacultural specialist for the Barnstable County Cooperative Extension said while putting oysters in the water is great, they can’t totally replace expensive sewering.

"I know a lot of the towns are looking at very large very expensive sewering projects and it’s certainly attractive to think we could just put shellfish in. Everybody loves to eat oysters and clams from our area and that just seems a lot less painless than the big bill that comes in with sewers," Murphy said. "I understand the desires for that, I think using them is a great complement to those systems but I’m not sure if they’re a complete replacement."

In three weeks time, these oysters will be mature enough to be placed in town waters in the wild, where they will filter out algae, and become part of the Cape ecosystem again.