New Calculator Helps Oyster Growers Measure the Water Quality Benefits of Farms

When it comes to removing excess nutrients from waterways, shellfish are a powerhouse. The NOAA Milford Lab in Connecticut studies the environmental benefits-also called ecosystem services-that shellfish provide. Nutrient removal is a particularly valuable ecosystem service.

Nutrients like nitrogen are essential to life, but often excess nutrients end up in coastal waters from human sources including lawn fertilizer and agricultural runoff. When this goes unchecked, algae can grow out of control. This can cause environmental problems including low dissolved oxygen, fish kills, and dead zones. Oysters and other bivalves-shellfish with two shells- help keep nutrients in check by filter feeding on algae. While they feed, these mighty shellfish improve water quality. This effect has been well documented by scientists, although it is not typically considered within the aquaculture permit review process.

Scientists from the Northeast Fisheries Science Center and the National Centers for Coastal Ocean Science created an online tool for oyster growers in the Northeast United States. They can use it to get a science-based estimate of how much nitrogen their farms remove from local waterways. The publicly available Aquaculture Nutrient Removal Calculator also generates a report that growers can include in their aquaculture permit applications. The team published the science behind this new tool in the journal PLOS ONE (open access). They are actively seeking feedback from the shellfish aquaculture community to help improve the tool. Send feedback to: [email protected].

"We've heard from both regulators and industry members that they need a simple, intuitive way to calculate the environmental benefits shellfish aquaculture provides," said project lead Julie Rose. "We're excited to share our tool, which synthesizes data collected by excellent scientists from around the region, to create a robust prediction of nitrogen removal that industry members and regulators can have confidence in."

Using the Aquaculture Nutrient Removal Calculator

To get an estimate of nitrogen removal, shellfish growers input the number of oysters they are harvesting and the average size of an oyster at harvest. The report also includes:

• Location of the farm
• Culture method (on-bottom, off-bottom, floating, or multiple methods)
• Ploidy (whether the oysters have two or three sets of chromosomes)
• Period of harvest

Importantly, it produces information about the ecosystem services a farm provides. It also provides supporting citations that can be included in an U.S. Army Corps of Engineers public interest review or a state-level permitting process. "We hope this tool will provide growers and managers with an easy-to-use way to generate defensible values and context for the ecosystem services provided by a proposed or existing farm," explained Schillaci.

Results from the calculator may also help shellfish growers build awareness of the environmental benefits of shellfish farming within their local communities.

Danielle Blacklock, Director of NOAA's Office of Aquaculture, explained, "Partnership with Sea Grant is key to sharing the tool with the shellfish aquaculture industry to use and provide feedback. NOAA relies on this feedback to develop aquaculture calculators and decision-support tools nationwide."

Building the Tool

To create the tool, the team synthesized a large dataset from 10 states from Maine to North Carolina. It included oyster size measurements and nitrogen concentrations in shell and tissue for farmed oysters across the Northeast United States coast. Organizations that shared data to support the calculator include:

• University of Maine
• University of New Hampshire
• Cape Cod Cooperative Extension in Massachusetts
• Environmental Protection Agency in Narragansett, Rhode Island
• NOAA Milford Lab in Connecticut
• Stony Brook University in New York
• Rutgers University in New Jersey
• NOAA National Ocean Service in Oxford, Maryland
• Maryland Sea Grant
• NOAA Chesapeake Bay Office
• University of North Carolina Wilmington

View the data.

Ryan Morse worked on the data management and app development aspects of the project. "The most time consuming aspect was compiling and performing quality control for the data that form the basis of the calculator," said Morse. "Because the data came in many different formats, we needed to standardize it before merging it into one dataset. After that, the analysis was fairly straightforward."

The team adapted methods that the Chesapeake Bay Program uses for nutrient management to calculate the amount of nitrogen removed when farmed oysters are harvested. NOAA's Office of Aquaculture funded the project. Connecticut Sea Grant's Regional Aquaculture Liaison Zach Gordon will hold a virtual workshop about the calculator for the northeast's Sea Grant Extension Network on Thursday, November 21 at 1 PM EST.

Expanding the Calculator

The calculator was built to incorporate new data and information as they become available. The research team plans to add phosphorus removal to the calculator for a more comprehensive estimate of nutrient removal. They also are scoping data availability to expand the nutrient calculator into the Gulf of Mexico.

Essential fish habitat is another valuable ecosystem service that shellfish farms provide. The team plans to create a calculator to estimate the habitat benefits that shellfish farms provide using data from the GoPro Aquaculture Project, which has collected more than 1,600 hours of underwater video on shellfish farms and rock reef comparison habitats in Long Island Sound. The fish habitat calculator will also draw from data collected by partner projects. The team sees opportunities on the horizon to extend the tools beyond oysters to other commonly farmed bivalve shellfish, such as clams and mussels.

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