The short version
Researchers from University of Maryland Extension and NOAA studied six working oyster farms in Maryland’s part of Chesapeake Bay. They estimated how many oysters each farm could produce, how much nitrogen those oysters remove, and what that cleanup would be worth if growers were paid for it. The answers varied widely from farm to farm, depending mostly on how well the oysters grew. The study supports including growers in nutrient trading programs, where they could sell credits for the nitrogen they remove.
What the researchers did
Oyster farming in Maryland’s Chesapeake Bay has grown fast; the number of farmed oysters harvested rose 10-fold after 2010. The Chesapeake Bay region has also approved harvested oysters as an official “best management practice” for nutrient reduction. Matt Parker and Suzanne Bricker set out to show what that could mean for individual growers.
- They sampled oysters and water quality at two bottom farms and four farms using cages in the water column, from May 2016 to August 2018. The leases ranged from 4 to 22 acres.
- They used the data to calibrate the FARM model, which estimates oyster growth, harvest and nitrogen removal at the scale of a single farm.
- They valued the nitrogen removed by comparing it with what it would cost to remove the same nitrogen through treatment plant upgrades, farm and urban stormwater practices, or existing credit markets.
What they found
- Harvests varied more than tenfold. Annual harvest ranged from 1.78 to about 25 metric tons of oysters per acre, depending on farming method, food in the water, salinity and losses to mortality.
- So did nitrogen removal. Estimated removal ranged from 28 to 457 kg of nitrogen per acre per year. The authors say this is consistent with rates reported elsewhere in the US and abroad.
- No harm to the water at the farms. Dissolved oxygen and ammonium at the farm sites did not change, suggesting there is room to expand carefully.
- Potentially real money for growers. Depending on which alternative cleanup method is used to set the price, the nitrogen removed was worth from about $560 to about $12.4 million a year per farm. The authors expect real credit prices in a trading market to fall at the low end of that range.
- Payment systems are arriving. Maryland’s Nutrient Trading Program has set up a way for oyster growers to earn credits, and the authors note that growers in the Chesapeake region and Massachusetts can already be credited for nitrogen removal.
What it means for Waquoit Bay today
For Waquoit Bay, the main lesson is that nitrogen removal by shellfish depends heavily on the site and the farming method, so local measurements matter. A farm in one cove may remove many times more nitrogen per acre than a farm in another. Numbers borrowed from elsewhere should be treated with caution until they are checked locally, as Cape Cod researchers have done for oysters and quahogs harvested here.
The study also shows one way to turn shellfish into a bigger part of a cleanup plan: pay growers for the nitrogen they remove. The authors conclude the approach is transferable to other waterbodies
(Parker & Bricker, 2020) that have both nutrient problems and oyster farming. Shellfish can supplement reductions in the septic nitrogen that drives Waquoit Bay’s problems; they don’t replace them.
Read the paper
Parker, M., & Bricker, S. (2020). Sustainable Oyster Aquaculture, Water Quality Improvement, and Ecosystem Service Value Potential in Maryland Chesapeake Bay. Journal of Shellfish Research, 39(2), 269–281. https://doi.org/10.2983/035.039.0208
License: Published by the National Shellfisheries Association and distributed through BioOne. The article is not openly licensed and BioOne limits use to personal, educational and non-commercial purposes, so we link to it rather than hosting a copy. The project was funded by NOAA Sea Grant.
Drafted with AI assistance from the linked source.
