Restoring Oysters Could Help Clean the Great Bay Estuary

Aug 19, 2010

This week, NHPR’s Amy Quinton has been taking a look at some of the challenges facing the Great Bay estuary.

Earlier she reported on how pollution is killing the bay’s eelgrass, a source of food and habitat for wildlife.

But the Bay also has lost most of its oysters, which help filter the water.
Pollution, disease, and overharvesting have all played a part.

As environment reporter Amy Quinton reports, an effort to restore oyster reefs may also help restore the balance of the ecosystem.

The Oyster River got its name for an obvious reason.

Years ago, it was home to more than one hundred acres of oysters.

Old maps suggest the reefs were two miles long.

Ray Konisky, Director of Marine Science at the Nature Conservancy, says that picture has changed dramatically.

“It’s a river that historically has been tremendous in terms of oyster growth and populations, not any more so, we’re down to probably a couple of acres of live oyster reefs.”

Ray Grizzle, a marine biologist with UNH’s Jackson Lab, says the mouths of all the rivers that flowed into the Great Bay once teemed with oysters.

“The major other beds were Central Great Bay near Nannie Island, and then the main stem of the Piscataqua apparently had huge long reefs we’ve got remnant shell from the General Sullivan all the way on up, they’re still approximately where they are, but the reefs were much less dense that’s the problem.”

Much less dense: all told, the Great Bay estuary has lost more than 90 percent of its oyster reefs.

The diseases MSX and Dermo wiped out much of the population.

But Grizzle says overharvest, poor water quality, and an influx of sediments are also part of the problem.

“Some of these tributaries are very dynamic with their sediment transport, when we had the spring of 06 flood, deposited about three inches of sediment on one of our reefs there, so you could lose them all in one flood.”

But UNH, the Nature Conservancy, and the Piscataqua Region Estuaries Partnership have partnered to help restore this once prolific shellfish.

On a 50 foot barge, a crane hoists a one ton bag of surf clam and quahog shells.
Crews guide the bag to the edge, untie the bottom and dump the shells into the Oyster River.

The Nature Conservancy’s Ray Konisky says 100 bags of shells will form a 100 by 400 foot reef that researchers hope oyster larvae will to cling to.

Last year, a pilot project showed success.

“Last year we caught about 1000 oysters for every one ton of shell we put down, so this year, we’re putting a hundred tons of shell down, so we hope to get by the end of the season, about 100-thousand live oysters at a minimum.”

Konisky says the more success the better because the average adult oyster can filter 20 gallons of water a day.

“There are excess sediments and excess nutrients, and oysters are able to survive in that even in the Oyster River we’re working in.”

Oysters filter the algae and phytoplankton that result from too much nitrogen.
That in turn could help the eelgrass that currently can’t survive in the Bay.

Again, UNH’s Ray Grizzle.

“No question that oysters remove nitrogen but it’s fairly complex as to how much, the form that it comes out in, and what happens to it thereafter.”

Grizzle says the idea of restoring enough oysters to clear the Bay of its pollution problems isn’t likely.

But oysters absorb nitrogen and researchers are exploring the idea of developing more oyster farms.

Perhaps growing them and then removing them for sale could also remove some of the nitrogen polluting the Bay.